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Item 8. Financial Statements and Supplementary Data

2026-02-20 compared with 2025-02-21 · 259 added, 262 removed, 1880 unchanged (22% of the section changed)

FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Alliant Energy Corporation and subsidiaries (the “Company”) as of December 31, 2024 and 2023, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2024, and the related notes and the schedules listed in the Index at Item 15 (collectively referred to as the “financial statements”).

We have audited the accompanying consolidated balance sheets of Alliant Energy Corporation and subsidiaries (the “Company”) as of December 31, 2025 and 2024, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2025, and the related notes and the schedule listed in the Index at Item 15 (collectively referred to as the “financial statements”).

In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2025 and 2024, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2025, in conformity with accounting principles generally accepted in the United States of America.

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Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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We identified the impact of rate regulation as a critical audit matter due to the significant judgments made by management to support its assertions about certain impacted account balances and disclosures and the high degree of subjectivity involved in assessing the impact of relevant future regulatory orders on the financial statements.

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We evaluated the external information and assessed whether there are matters in such information that would be contradictory to management’s assertion of probability of recovery of certain regulatory assets or refund of regulatory liabilities, or impact other recorded balances.

• We inspected minutes of the board of directors and other committees of the Company, regulatory orders and other filings with the regulatory agencies to identify evidence that may contradict management’s assertion regarding probability of abandonment or that may have an impact on the recorded balances.

• We obtained representation from management asserting that regulatory assets recorded in the financial statements are probable of recovery and that obligations to make refunds to customers are appropriately recorded as regulatory liabilities.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

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We have served as the Company’s auditor since 2002.

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ALLIANT ENERGY CORPORATION

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Diluted 257.8 256.8 253.3

Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) $ 2.69 $ 2.78 $ 2.73

Earnings per weighted average common share attributable to Alliant Energy common shareowners:

Basic $ 3.15 $ 2.69 $ 2.78

Diluted $ 3.14 $ 2.69 $ 2.78

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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Accounts payable 498 532

Accrued interest 124 112

Regulatory liabilities 88 69

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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Accounts receivable ( 652 ) ( 547 ) ( 414 )

Regulatory assets 70 24 ( 108 )

Derivative assets 6 13 149

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Deferred income taxes (a) 252 259 84

Pension and other benefit obligations ( 25 ) ( 28 ) ( 97 )

Other ( 116 ) 66 ( 35 )

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Net cash flows from financing activities 1,202 398 573

Net increase (decrease) in cash, cash equivalents and restricted cash 18 39 ( 16 )

Net increase in cash, cash equivalents and restricted cash 475 18 39

Cash, cash equivalents and restricted cash at beginning of period 81 63 24

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Interest ($ 500 ) ($ 434 ) ($ 378 )

Income taxes, net (a)

Income taxes, net:

Federal (a) $ 271 $ 202 $ 82

State - Iowa ( 5 ) ( 5 ) 6

Total income taxes, net

$ 266 $ 197 $ 88

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Beneficial interest obtained in exchange for securitized accounts receivable $ 126 $ 163 $ 216

(a) 2024 and 2023 include $ 216 million and $ 98 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

(a) 2025, 2024 and 2023 include $ 285 million, $ 216 million and $ 98 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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( 456 ) ( 456 )

Shareowner Direct Plan issuances 25 25

At-the-market offering program, net and Shareowner Direct Plan issuances 246 246

Equity-based compensation plans and other 7 7

Other comprehensive income, net of tax 1 1

Ending balance 3 3,030 3,756 1 ( 13 ) 6,777

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( 492 ) ( 492 )

At-the-market offering program, net and Shareowner Direct Plan issuances 246 246

Shareowner Direct Plan issuances 23 23

Equity-based compensation plans and other 7 ( 1 ) 6

Other comprehensive income, net of tax 1 1

Ending balance 3 3,060 3,954 1 ( 14 ) 7,004

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Interstate Power and Light Company and subsidiaries (the “Company”) as of December 31, 2024 and 2023, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2024, and the related notes and the schedule listed in the Index at Item 15 (collectively referred to as the “financial statements”).

We have audited the accompanying consolidated balance sheets of Interstate Power and Light Company and subsidiaries (the “Company”) as of December 31, 2025 and 2024, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2025, and the related notes (collectively referred to as the “financial statements”).

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Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

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We have served as the Company’s auditor since 2002.

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INTERSTATE POWER AND LIGHT COMPANY

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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Derivative assets 4 6 84

Accounts payable 31 ( 68 ) 65

Regulatory liabilities 20 ( 61 ) ( 92 )

Deferred income taxes (a) 194 178 36

Pension and other benefit obligations ( 5 ) ( 11 ) ( 65 )

Other ( 60 ) 57 ( 140 )

Net cash flows from operating activities 286 357 261

Cash flows from (used for) investing activities:

Cash flows used for investing activities:

Construction and acquisition expenditures ( 1,473 ) ( 1,224 ) ( 712 )

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Other ( 14 ) ( 53 ) ( 67 )

Net cash flows from (used for) investing activities ( 684 ) ( 326 ) 215

Cash flows from (used for) financing activities:

Net cash flows used for investing activities ( 859 ) ( 684 ) ( 326 )

Cash flows from financing activities:

Common stock dividends ( 359 ) ( 200 ) ( 280 )

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Other ( 1 ) ( 15 ) 7

Net cash flows from (used for) financing activities 303 103 ( 317 )

Net cash flows from financing activities 551 303 103

Net increase (decrease) in cash, cash equivalents and restricted cash ( 22 ) ( 24 ) 38

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Interest ($ 212 ) ($ 169 ) ($ 150 )

Income taxes, net (a)

Income taxes, net:

Federal (a) $ 142 $ 164 $ 98

State - Iowa ( 3 ) 11 19

Total income taxes, net

$ 139 $ 175 $ 117

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Beneficial interest obtained in exchange for securitized accounts receivable $ 126 $ 163 $ 216

(a) 2024 and 2023 includes $ 117 million and $ 76 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

(a) 2025, 2024 and 2023 include $ 140 million, $ 117 million and $ 76 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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Common stock dividends ( 280 ) ( 280 )

Capital contributions from parent 80 80

Ending balance 33 2,887 1,054 3,974

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Wisconsin Power and Light Company and subsidiaries (the “Company”) as of December 31, 2024 and 2023, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2024, and the related notes and the schedule listed in the Index at Item 15 (collectively referred to as the “financial statements”).

We have audited the accompanying consolidated balance sheets of Wisconsin Power and Light Company and subsidiaries (the “Company”) as of December 31, 2025 and 2024, the related consolidated statements of income, equity, and cash flows, for each of the three years in the period ended December 31, 2025, and the related notes (collectively referred to as the “financial statements”).

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Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

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We have served as the Company’s auditor since 2002.

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WISCONSIN POWER AND LIGHT COMPANY

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Income before income taxes 387 356 405

Income taxes 11 60 66

Income tax expense (benefit) ( 14 ) 11 60

Net income $ 401 $ 345 $ 345

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

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Depreciation and amortization 370 357 280

Equity component of allowance for funds used during construction ( 23 ) ( 59 ) ( 36 )

Other ( 63 ) ( 51 ) ( 47 )

Other changes in assets and liabilities:

Accounts receivable ( 56 ) ( 5 ) 23

Regulatory assets 43 72 ( 34 )

Derivative assets 7 65 ( 7 )

Accounts payable 50 ( 57 ) 22

Regulatory liabilities 120 ( 41 ) ( 57 )

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Net cash flows used for investing activities ( 827 ) ( 724 ) ( 946 )

Cash flows from financing activities:

Cash flows from (used for) financing activities:

Common stock dividends ( 207 ) ( 196 ) ( 184 )

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Proceeds from issuance of long-term debt 296 297 297

Payments to retire long-term debt — — ( 250 )

Net change in commercial paper ( 183 ) ( 135 ) 28

Other ( 9 ) ( 14 ) ( 16 )

Net cash flows from financing activities 7 370 737

Net increase in cash, cash equivalents and restricted cash 44 2 3

Net cash flows from (used for) financing activities ( 23 ) 7 370

Net increase (decrease) in cash, cash equivalents and restricted cash ( 14 ) 44 2

Cash, cash equivalents and restricted cash at beginning of period 51 7 5

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Interest ($ 176 ) ($ 163 ) ($ 146 )

Income taxes, net (a)

Income taxes, net:

Federal (a) $ 124 $ 41 ($ 25 )

State - Wisconsin ( 15 ) ( 27 ) ( 25 )

Total income taxes, net

$ 109 $ 14 ($ 50 )

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Accrued capital expenditures $ 71 $ 87 $ 217

(a) 2024 and 2023 includes $ 99 million and $ 22 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

(a) 2025, 2024 and 2023 include $ 145 million, $ 99 million and $ 22 million, respectively, of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

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Capital contributions from parent 245 245

Other ( 1 ) ( 1 )

Ending balance 66 2,478 1,353 3,897

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa.

IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa.

In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative will expire.

IPL also sells electricity to wholesale customers in Illinois and Iowa.

In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired.

IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Cedar Rapids, Iowa through 2025.

WPL’s financial statements include the accounts of WPL and its consolidated subsidiaries.

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freight brokerage services;

wind turbine blade recycling services;

and a rail-served warehouse in Iowa.

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Actual results could differ from those estimates.

NOTE 1 (b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions.

NOTE 1 (b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories.

As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities.

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Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.

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NOTE 1 (c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements.

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IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).

The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers.

In 2023 and 2024, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash.

IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash.

Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities.

For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price.

Renewable tax credits and any related valuation allowances are derecognized when control of the tax credits is transferred to other corporate taxpayers.

Renewable tax credits subject to future transfer are recorded at expected realizable value.

Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers.

Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism.

Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold;

any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years.

At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements.

At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements.

An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

Refer to Notes 1 1 and 1 6 (d) for further discussion of the transfer of renewable tax credits to other corporate taxpayers, including related valuation allowances and indemnification requirements, respectively.

Refer to Note 1 6 (d) for further discussion of the indemnification requirements.

NOTE 1 (d) Cash, Cash Equivalents and Restricted Cash - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days.

At December 31, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $ 52 million, $ 9 million, and $ 43 million, respectively, of money market fund investments, with weighted average interest rates of 4 %.

At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $ 411 million and $ 25 million, respectively, of money market fund investments, with weighted average interest rates of 4 %.

At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.

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However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.

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Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions.

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Other 5.6 % 4.6 % 6.2 % 4.5 % 4.4 % 4.6 %

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024.

IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8 % and 3.0 %, respectively, during 2025.

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting.

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WPL may be authorized to apply its AFUDC rates to 100 % of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order.

Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.

Non-utility and Other Property -

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As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.

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IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO.

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Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity.

Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are primarily recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements.

Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements.

The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

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The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

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WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings.

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Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements.

The cumulative effects of the under-/over-collection of these costs for IPL are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

Refer to Note 1(c) for further discussion of the treatment of IPL’s renewable tax credits for rate-making purposes.

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If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.

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Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable.

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If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value.

Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed.

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Refer to Note 13 for details of an ARO charge for steam assets at IPL in 2024.

NOTE 1 (k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others.

Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.

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Finance lease expense is comprised of depreciation and amortization, and interest expenses.

Finance lease assets related to leased land for solar generation are accounted for as operating leases for rate-making purposes.

All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.

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Finance lease assets are accounted for as operating leases for rate-making purposes.

REGULATORY MATTERS

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Assets retired early 158 180 149 168 9 12

Commodity cost recovery 68 120 2 12 66 108

Derivatives 60 102 15 34 45 68

Non-service pension and OPEB costs 57 51 21 19 36 32

Derivatives 52 60 12 15 40 45

WPL’s Western Wisconsin gas distribution expansion investments 39 42 — — 39 42

IPL’s DAEC PPA amendment 18 42 18 42 — —

Commodity cost recovery 10 68 3 2 7 66

Other 140 168 34 74 106 94

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At December 31, 2025, IPL and WPL had $ 165 million and $ 28 million, respectively, of regulatory assets that were not earning a return on investment.

IPL’s regulatory assets that were not earning a return consisted primarily of the retired Lansing Generating Station, retired analog electric meters, emission allowances and costs for certain construction projects.

WPL’s regulatory assets that were not earning a return consisted primarily of costs for certain construction projects.

IPL’s regulatory assets that were not earning a return consisted primarily of the retired Lansing Generating Station, retired analog electric meters, and costs for certain construction projects.

WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the retail portion of under-collected electric transmission service expenses and costs for certain construction projects.

The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost.

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These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates.

Refer to Note 11 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2024.

AROs - Alliant Energy, IPL and WPL believe it is probable that certain differences between expenses accrued for AROs related to their utility operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets.

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Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):

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Entity Asset Retirement Date Regulatory Asset Balance as of Dec.

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(a) The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.

(b) IPL was previously allowed a full recovery of and a full return on the Lansing Generation Station from both its retail and wholesale customers.

(b) IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers.

The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024.

As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $ 60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms.

The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding.

In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 117 million deferral as of December 31, 2022, which WPL is collecting from October 2023 through December 2025 from its retail electric customers, plus interest ($ 12 million and $ 50 million was collected in 2023 and 2024, respectively).

In 2023, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 34 million regulatory liability as of December 31, 2023, which was refunded in 2024 to its retail electric customers, plus interest.

Non-service pension and OPEB costs - Non-service pension and OPEB costs are recorded to regulatory assets to reflect the impacts of rate-making, and are recovered from IPL’s and WPL’s electric and gas customers through depreciation expense based on the depreciation rates for plant in-service.

Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized.

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Refer to Note 14 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project.

Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040.

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $ 110 million in exchange for shortening the term of its DAEC PPA by 5 years.

The buyout payment, including a return on, is being recovered from IPL’s retail and wholesale customers from 2021 through 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms.

In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 117 million deferral as of December 31, 2022, which WPL substantially collected from October 2023 through December 2025 from its retail electric customers, plus interest ($ 12 million, $ 50 million and $ 52 million was collected in 2023, 2024 and 2025, respectively).

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):

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Derivatives 47 53 26 29 21 24

Commodity cost recovery 17 48 12 13 5 35

Other 98 46 39 26 59 20

$ 1,201 $ 1,028 $ 586 $ 546 $ 615 $ 482

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Tax-related regulatory liabilities reduce revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings.

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These rules limit the rate at which these tax benefits are allowed to be passed on to customers.

The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in 2024.

A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.

Additionally, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities include tax benefits resulting from investment tax credits for IPL’s and WPL’s energy storage facilities and WPL’s Cassville solar facility.

Refer to Note 1 (c) for details related to the regulatory treatment of IPL’s and WPL’s investment tax credits.

Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated AROs or that have removal costs in addition to AROs.

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Refer to Note 3 for discussion of PSCW orders approving deferral of, and the deferral of a return on, incremental solar generation construction costs in 2024 and 2025.

WPL’s Retail Fuel-related Rate Filing (2021 Forward-looking Test Period) - In 2023, WPL collected $ 37 million, plus interest, from its retail electric customers related to actual fuel-related costs for 2021 that were higher than fuel-related costs used to determine rates for such period.

WPL’s Retail Electric and Gas Rate Reviews (2026/2027 Forward-looking Test Period) - In December 2025, the PSCW issued an order authorizing annual base rate increases of $ 69 million and $ 7 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2026, for the 2026 forward-looking Test Period.

The PSCW’s order also authorized WPL to implement an additional $ 75 million and $ 5 million increase in annual rates for its retail electric and gas customers, respectively, effective January 1, 2027, for the 2027 forward-looking Test Period.

IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $ 185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $ 10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period.

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• Discontinuation of the renewable energy rider.

Table of C o ntents

PROPERTY, PLANT AND EQUIPMENT

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Electric plant:

Generation in service (a)(b) $ 11,156 $ 9,180 $ 5,924 $ 5,025 $ 5,232 $ 4,155

Generation and energy storage in service (a)(b) $ 12,757 $ 11,156 $ 6,251 $ 5,924 $ 6,506 $ 5,232

Distribution in service 8,418 7,811 4,691 4,344 3,727 3,467

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Gas plant in service 1,938 1,863 1,020 981 918 882

Other plant in service (d) 734 653 456 411 278 242

Other plant in service 752 734 456 456 296 278

Accumulated depreciation (c) ( 6,690 ) ( 6,229 ) ( 3,574 ) ( 3,360 ) ( 3,116 ) ( 2,869 )

Net plant 17,747 16,714 9,213 8,730 8,534 7,984

Leased Sheboygan Falls Energy Facility, net (e) — — — — 74 79

Leased Sheboygan Falls Energy Facility, net (d) — — — — 110 74

Leased land for solar generation, net 190 189 52 53 138 136

Construction work in progress 1,215 1,245 548 605 667 640

Construction work in progress (e) 1,742 1,215 1,166 548 576 667

Other, net 10 5 5 5 5 —

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Total property, plant and equipment $ 20,344 $ 18,701 $ 10,436 $ 9,336 $ 9,363 $ 8,861

(a) Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $ 205 million.

(a) Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $ 205 million.

In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025.

Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.

(b) In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $ 1,650 /kilowatt up to $ 1,837.5 /kilowatt.

The costs up to the original cost target of $ 1,650 /kilowatt will earn a return on common equity of 10.25 %.

The costs between $ 1,650 /kilowatt and $ 1,837.5 /kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred.

Alliant Energy and IPL currently do not expect these construction costs will exceed $ 1,837.5 /kilowatt.

WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas.

Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024.

As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $ 413 million and $ 428 million, respectively.

As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment.

In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals.

As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment.

WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.

(d) Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024.

IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.

(e) Less accumulated amortization of $ 116 million and $ 112 million for WPL as of December 31, 2024 and 2023, respectively.

Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024.

In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers.

As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.

(b) WPL’s Grant County ( 100 MW) and Wood County ( 75 MW) energy storage facilities, and IPL’s Wever ( 99 MW) energy storage facility, were placed in service in 2025.

As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment.

WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas.

As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.

(d) Less accumulated amortization of $ 120 million and $ 116 million for WPL as of December 31, 2025 and 2024, respectively.

Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025.

For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.

(e) Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.

(f) Less accumulated depreciation of $ 81 million and $ 78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.

(g) Less accumulated depreciation of $ 305 million and $ 289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.

Table of C o ntents

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting.

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a Mississippi River barge, rail and truck freight terminal in Illinois;

wind turbine blade recycling services;

and a rail-served warehouse in Iowa).

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Columbia Units 1-2 and Energy Storage System 53.5 % 868 407 4

West Riverside Energy Center and Solar Facility (a) 56.6 % 449 59 5

West Riverside Energy Center and Solar Facility 56.6 % 456 71 7

Forward Wind Energy Center 42.6 % 118 58 —

Alliant Energy $ 2,541 $ 1,064 $ 27

(a) In 2023 and 2024, WEC Energy Group, Inc.

and Madison Gas and Electric Company acquired partial ownership interests in West Riverside.

The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.

Table of C o ntents

NOTE 5 (a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):

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Originated in 2024

Originated in 2025

Alliant Energy $ 1 $ 12 $ 16

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The limit on cash proceeds fluctuates between $ 5 million and $ 110 million, which IPL may change periodically throughout the year.

As of December 31, 2024, the limit on cash proceeds was $ 110 million and IPL had $ 40 million of available capacity under its sales of accounts receivable program.

As of December 31, 2025, the limit on cash proceeds was $ 110 million and IPL had no available capacity under its sales of accounts receivable program.

Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less.

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Unbilled utility revenues 104 108

Other receivables — 1

Receivables sold to third party 251 245

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Write-offs, net of recoveries 12 12 12

Table of C o ntents

Unconsolidated Equity Investments - Alliant Energy’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):

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ATC is an independent, for-profit, transmission-only company.

ATC Holdco LLC holds Duke-American Transmission Company, LLC, a joint venture between Duke Energy Corporation and ATC, that owns electric transmission infrastructure in North America.

Refer to Note 1 6 (g) for discussion of a reduction in earnings recorded in 2022 related to a court decision, and subsequent FERC order, which reduced the base return on equity authorized for MISO transmission owners, including ATC.

ATC Holdco LLC holds an interest in Duke-American Transmission Company, LLC, which holds a note receivable related to previously owned electric transmission infrastructure in North America.

Non-utility Wind Farm in Oklahoma - The non-utility wind farm located in Oklahoma provides electricity to a third-party under a long-term PPA, and has both cash and tax equity ownership.

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This at-the-market offering program has expired.

In May 2025, Alliant Energy filed a prospectus supplement and executed a related distribution agreement, under which it may sell up to $ 1.3 billion in aggregate of its common stock through 2028 through an at-the-market offering program that includes an equity forward sales component.

Alliant Energy expects to use proceeds from the issuance of common stock for general corporate purposes.

Alliant Energy entered into forward sale agreements under its at-the-market offering program with various counterparties who, for the quarter and year ended December 31, 2025, borrowed and sold an aggregate of 3,831,429 and 14,595,532 shares of Alliant Energy common stock at an aggregate gross sales price of $ 258 million and $ 944 million, including approximately $ 2 million and $ 7 million in commissions, respectively, to the counterparties payable by Alliant Energy when the forward sale agreements are settled.

Alliant Energy has not yet received any proceeds from this program and no amounts have been or will be recorded in equity on Alliant Energy’s balance sheets until the forward sale agreements settle.

Alliant Energy currently expects to settle the forward sale agreements in 2026 and 2027 through physical delivery of shares of common stock in exchange for cash proceeds at the then-applicable forward sale price;

however, Alliant Energy may elect cash settlement or net share settlement for all or a portion of the obligations under the forward sale agreements.

As of December 31, 2025, the weighted-average forward price, net of commissions, was $ 64.44 per share and is subject to daily adjustment based on a floating interest rate factor and decreased by other fixed amounts specified in the forward sale agreements.

As of December 31, 2025, Alliant Energy could have settled all of its outstanding forward sale agreements under the at-the-market offering program with physical delivery of 14,595,532 shares of Alliant Energy common stock to the counterparties in exchange for cash of $ 941 million.

Alliant Energy has concluded that the forward sale agreements meet the derivative scope exception for certain contracts involving an entity’s own equity.

Until settlement of the forward sale agreements, Alliant Energy’s EPS dilution resulting from the agreements, if any, is determined using the treasury stock method.

Share dilution occurs when the average market price of Alliant Energy stock during the reporting period is higher than the forward sale price as of the end of the reporting period.

As of December 31, 2025, 569,944 incremental shares were included in the calculation of diluted EPS related to the securities under the forward sale agreements.

Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market.

Table of C o ntents

NOTE 8 (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding.

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Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $ 1 billion, $ 400 million and $ 500 million, respectively, within the $ 1.3 billion total commitment.

Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):

Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):

Alliant Energy IPL WPL

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Weighted average interest rates 4.5 % 5.3 % 4.6 % 5.1 % 4.5 % 5.4 %

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NOTE 8 (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):

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— — — 250 250 —

5.5 %, (Retired in 2025)

— — — 50 50 —

4,725 4,725 — 4,125 4,125 —

Debentures (a):

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300 — 300 300 — 300

5.375 %, due 2034 (c)

5.375 %, due 2034

300 — 300 300 — 300

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350 — 350 350 — 350

5.7 %, due 2055 (c)

300 — 300 — — —

3,700 — 3,700 3,400 — 3,400

AEF term loan credit agreement through March 2026, 5 % at December 31, 2025 (with Alliant Energy as guarantor) (d)

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575 — — 575 — —

AEF 5.4 % senior notes, due 2027 (with Alliant Energy as guarantor) (a)(f)

AEF 5.4 % senior notes, due 2027 (with Alliant Energy as guarantor) (a)

375 — — 375 — —

Alliant Energy 3.25 % convertible senior notes, due 2028 (e)

575 — — — — —

AEF 4.25 % senior notes, due 2028 (with Alliant Energy as guarantor) (a)

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350 — — 350 — —

Alliant Energy 5.75 % junior subordinated notes, due 2056 (f)

725 — — — — —

AEF term loan credit agreement, 6 % at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)

— — — 300 — —

Sheboygan Power, LLC 5.06 % senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)

3,700 — — 2,400 — —

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Treasury rates at the time of redemption.

Table of C o ntents

(b) In September 2024, IPL issued $ 350 million of 4.95 % senior debentures due 2034 and $ 300 million of 5.45 % senior debentures due 2054.

A portion of the net proceeds was used for the retirement of IPL’s $ 500 million 3.25 % senior debentures, and the remainder of the net proceeds was used for general corporate purposes.

The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.

(d) In March 2024, AEF entered into a $ 300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2024, and retired the $ 300 million variable rate term loan set forth therein.

(b) In May 2025, IPL issued $ 600 million of 5.6 % senior debentures due 2035.

A portion of the net proceeds was used for the retirement of IPL’s $ 50 million 5.5 % senior debentures and $ 250 million 3.4 % senior debentures.

The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes.

In September 2025, IPL issued $ 300 million of 5.6 % senior debentures due 2055.

The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.

The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.

(d) In March 2025, AEF entered into a $ 300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $ 300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity.

AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $ 100 million.

Refer to Note 14 for information on AEF’s related interest rate swap.

In January 2026, AEF retired its $ 300 million term loan.

(e) Refer to “ Convertible Senior Notes ” below for additional information.

(f) In June 2024, AEF issued $ 375 million of 5.4 % senior notes due 2027.

The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

(f) In September 2025, Alliant Energy issued $ 725 million of junior subordinated notes due 2056.

The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S.

Treasury rate plus a spread of 2.077 %, provided the interest rate will not reset below 5.75 %.

The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes.

Long term debt to be retired includes AEF’s $ 300 million variable rate term loan which was retired in January 2026, AEF’s $ 200 million of 1.4 % senior notes and Alliant Energy’s $ 575 million of 3.875 % convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity.

Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.

(g) There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes - In March 2023, Alliant Energy issued $ 575 million of 3.875 % convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes.

Convertible Senior Notes

2026 Notes - In March 2023, Alliant Energy issued $ 575 million of 3.875 % convertible senior notes (the 2026 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes.

The 2026 Notes will mature on March 15, 2026 unless earlier converted or repurchased.

Alliant Energy may not redeem the 2026 Notes prior to the maturity date.

Holders may convert their Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

Holders could have converted their 2026 Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

• during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130 % of the conversion price on each applicable trading day during such period;

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On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2026 Notes at any time, regardless of the foregoing circumstances.

Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the Notes being converted.

Upon conversion of the 2026 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2026 Notes to be converted and deliver shares of its common stock, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2026 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $ 1,000 principal amount of 2026 Notes (equivalent to an initial conversion price of approximately $ 64.32 per share of Alliant Energy’s common stock).

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If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2026 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2026 Notes at a fundamental change repurchase price equal to 100 % of the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met.

As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively.

As of December 31, 2025 and 2024, the 2026 Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt”.

As of December 31, 2025 and 2024, the net carrying amount of the 2026 Notes was $ 574 million and $ 571 million , with unamortized debt issuance costs of $ 1 million and $ 4 million, and the estimated fair value (Level 2) of the 2026 Notes was $ 599 million and $ 591 million.

As of December 31, 2025, there were 407,821 shares of Alliant Energy’s common stock related to the potential conversion of the 2026 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2026 Notes.

2028 Notes - In May 2025, Alliant Energy issued $ 575 million of 3.25 % convertible senior notes (the 2028 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

The 2028 Notes will mature on May 30, 2028 unless earlier converted or repurchased, and no sinking fund is provided for the 2028 Notes.

Alliant Energy may not redeem the 2028 Notes prior to the maturity date.

Holders may convert their 2028 Notes at their option at any time prior to the close of business on the business day immediately preceding March 1, 2028 only under the following circumstances:

• during any calendar quarter commencing after the calendar quarter ending on September 30, 2025 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130 % of the conversion price on each applicable trading day during such period;

• during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $ 1,000 principal amount of 2028 Notes for each trading day of the measurement period was less than 98 % of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day;

• upon the occurrence of specified corporate events.

O n or after March 1, 2028 until the cl ose of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2028 Notes at any time, regardless of the foregoing circumstances.

Upon conversion of the 2028 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2028 Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2028 Notes being converted.

The initial conversion rate is 13.1773 shares of common stock per $ 1,000 principal amount of 2028 Notes (equivalent to an initial conversion price of approximately $ 75.89 per share of Alliant Energy’s common stock).

The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest.

In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2028 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2028 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2028 Notes at a fundamental change repurchase price equal to 100 % of the principal amount of the 2028 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2025, the conditions allowing holders of the 2028 Notes to convert their 2028 Notes were not met, and the 2028 Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet.

As of December 31, 2025, the net carrying amount was $ 569 million, with unamortized debt issuance costs of $ 6 million, and the estimated fair value (Level 2) was $ 587 million for the 2028 Notes.

As of December 31, 2025, there were no shares of Alliant Energy’s common stock related to the potential conversion of the 2028 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2028 Notes.

Table of C o ntents

Five-Year Schedule of Long-term Debt Maturities - At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):

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There are no lease renewal periods remaining.

In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement.

For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

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Sheboygan Falls Energy Facility N/A N/A $ 4 N/A N/A $ 7

Leased land for solar generation $ — $ — — $ — $ — —

$ — $ — $ 4 $ — $ — $ 7

Other liabilities:

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Total finance lease expense $ 9 $ 8 $ 7 $ 3 $ 2 $ 1 $ 13 $ 14 $ 14

Table of C o ntents

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):

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IPL provides retail electric and gas service to customers in Iowa, and WPL provides retail and wholesale electric and retail gas service to customers in Wisconsin.

IPL also provides electricity to wholesale customers in Minnesota, Illinois and Iowa, as well as steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa.

IPL also provides electricity to wholesale customers in Illinois and Iowa.

IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired in July 2025.

IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa through 2025.

IPL’s and WPL’s retail electric and gas revenues include sales to residential, commercial and industrial customers.

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freight brokerage services;

wind turbine blade recycling services;

and a rail-served warehouse in Iowa.

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Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):

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($ 149 ) ($ 114 ) $ 4 ($ 127 ) ($ 129 ) ($ 58 ) ($ 14 ) $ 11 $ 60

Table of C o ntents

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.

In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $ 60 million for IPL’s Lansing Generation Station discussed in Note 2 .

Alliant Energy IPL WPL

In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $ 60 million for IPL’s Lansing Generating Station discussed in Note 2 .

In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures.

Previously reported information for prior periods has been recast to conform with current period presentation.

Alliant Energy 2025 2024 2023

Amount Tax Rate Amount Tax Rate Amount Tax Rate

Statutory federal income tax rate $ 139 21 % $ 121 21 % $ 149 21 %

State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin) 22 3 4 1 21 3

Production tax credits ( 206 ) ( 31 ) ( 171 ) ( 30 ) ( 121 ) ( 17 )

Investment tax credits ( 156 ) ( 24 ) ( 42 ) ( 7 ) ( 3 ) —

Research and development credits ( 2 ) — ( 6 ) ( 1 ) — —

Tax credit regulatory deferrals (Refer to Note 1 (c) and Note 2 )

112 17 20 3 2 —

Other credits ( 1 ) — — — — —

Nontaxable or nondeductible items 4 1 2 — ( 2 ) —

Other adjustments:

Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)

( 37 ) ( 6 ) ( 33 ) ( 6 ) ( 27 ) ( 4 )

Amortization of excess deferred taxes (Refer to Note 2 )

( 24 ) ( 4 ) ( 13 ) ( 2 ) ( 13 ) ( 2 )

Other — — 4 1 ( 2 ) —

Total income tax expense (benefit) and overall income tax rate ($ 149 ) ( 23 %) ($ 114 ) ( 20 %) $ 4 1 %

IPL 2025 2024 2023

Amount Tax Rate Amount Tax Rate Amount Tax Rate

Statutory federal income tax rate $ 69 21 % $ 49 21 % $ 65 21 %

State income taxes, net of federal benefits ( 1 ) 2 3 ( 12 ) ( 2 ) ( 2 ) 6 5 6

State income taxes, net of federal benefits (primarily from state income taxes in Iowa) ( 10 ) ( 3 ) ( 27 ) ( 12 ) ( 5 ) ( 2 )

Production tax credits ( 133 ) ( 40 ) ( 108 ) ( 46 ) ( 95 ) ( 31 )

Investment tax credits ( 43 ) ( 13 ) ( 8 ) ( 4 ) ( 2 ) ( 1 )

Tax credit regulatory deferrals (Refer to Note 1 (c) and Note 2 )

42 13 4 1 1 —

Other credits ( 1 ) — ( 1 ) — — —

Nontaxable or nondeductible items 1 — ( 1 ) — ( 1 ) —

Other adjustments:

Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)

( 30 ) ( 9 ) ( 24 ) ( 10 ) ( 16 ) ( 5 )

Amortization of excess deferred taxes (Refer to Note 2 )

( 22 ) ( 7 ) ( 13 ) ( 5 ) ( 5 ) ( 1 )

Effect of rate-making on property-related differences ( 5 ) ( 4 ) ( 1 ) ( 10 ) ( 5 ) ( 1 ) ( 1 ) ( 3 ) ( 2 )

Other items, net 1 1 — ( 1 ) — 2 — 1 —

Overall income tax rate ( 20 %) 1 % 3 % ( 55 %) ( 19 %) ( 16 %) 3 % 15 % 17 %

Total income tax expense (benefit) and overall income tax rate ($ 127 ) ( 38 %) ($ 129 ) ( 55 %) ($ 58 ) ( 19 %)

WPL 2025 2024 2023

Amount Tax Rate Amount Tax Rate Amount Tax Rate

Statutory federal income tax rate $ 81 21 % $ 75 21 % $ 85 21 %

State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin) 27 7 23 7 22 5

Production tax credits ( 73 ) ( 19 ) ( 63 ) ( 18 ) ( 26 ) ( 6 )

Investment tax credits ( 114 ) ( 29 ) ( 34 ) ( 10 ) ( 1 ) —

Tax credit regulatory deferrals (Refer to Note 1 (c) and Note 2 )

70 18 17 4 1 —

Other credits — — ( 1 ) — — —

Nontaxable or nondeductible items 1 — ( 1 ) — ( 2 ) —

Other adjustments:

Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)

( 6 ) ( 2 ) ( 5 ) ( 1 ) ( 12 ) ( 4 )

Amortization of excess deferred taxes (Refer to Note 2 )

— — — — ( 7 ) ( 1 )

Total income tax expense (benefit) and overall income tax rate ($ 14 ) ( 4 %) $ 11 3 % $ 60 15 %

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

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Federal tax credits 2034-2045 669 455 199

Valuation Allowances - Refer to N ote 1 (c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers.

State Income Tax Apportionment - Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements.

Deferred taxes are recorded using currently enacted tax rates and estimates of state income tax apportionment.

Estimates of state income tax apportionment are supported by historical data and reasonable projections.

Alliant Energy currently expects an increase in total state income tax apportionment primarily due to an increase in projected electric utility revenues driven by demand for energy from commercial and industrial customers, including demand from IPL’s and WPL’s executed electric service agreements with customers who expect to build data centers in their service territories.

Alliant Energy parent company’s deferred tax assets were remeasured to reflect an increase in estimated total state income tax apportionment, which resulted in a charge of $ 8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in 2025.

Uncertain Tax Positions - At December 31, 2025, 2024 and 2023, there were no uncertain tax positions or penalties accrued related to uncertain tax positions.

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(a) The 2021 and 2022 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return.

(a) The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return.

The statute of limitations for these federal tax returns expires three years from each filing date.

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Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met.

These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5 %, compared to the 9.8 % Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted.

In 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4 % effective January 1, 2023, and 7.1 % effective January 1, 2024, respectively.

In 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1 % effective January 1, 2024.

Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled.

Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $ 77 million and $ 74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively.

Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2023 based upon the new rate effective January 1, 2024, which resulted in a $ 74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2023.

In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year.

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The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $ 8 million, $ 10 million and $ 11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 2023 and 2024, respectively.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $ 10 million and $ 11 million recorded to income tax expense in Alliant Energy’s income statements and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2023 and 2024, respectively.

Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

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Rate of compensation increase 4.00 % 3.75 % 3.30 % N/A N/A N/A

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Qualified Defined Benefit Pension Plan OPEB Plans

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Amortization of actuarial loss (c) 22 24 28 — — 1

Settlement losses (d) — — 26 — — —

$ 19 $ 18 $ 26 $ 5 $ 5 $ 7

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Amortization of actuarial loss (c) 9 9 11 — — 1

Settlement losses (d) — — 13 — — —

$ 7 $ 6 $ 9 $ — $ — $ 2

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Amortization of actuarial loss (c) 11 11 13 — — 1

Settlement losses (d) — — 13 — — —

$ 9 $ 10 $ 13 $ 3 $ 3 $ 4

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(c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

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(d) Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans.

In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $ 7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

Benefit Plan Assets and Obligations - A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):

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Fair value of plan assets at December 31 346 340 60 59

Under funded status at December 31 ($ 32 ) ($ 35 ) $ — ($ 4 )

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(Under) Over funded status at December 31 ($ 17 ) ($ 32 ) $ 1 $ —

Defined Benefit Pension Plans OPEB Plans

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Fair value of plan assets 747 715 N/A N/A

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Defined Benefit Pension Plans OPEB Plans

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Plans with accumulated benefit obligations in excess of plan assets:

Accumulated benefit obligations 362 377 N/A 65

Fair value of plan assets 340 352 N/A 61

Accumulated benefit obligations 353 362 N/A N/A

Fair value of plan assets 346 340 N/A N/A

Plans with projected benefit obligations in excess of plan assets:

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$ 38 $ 37 $ 36 $ 36 $ 35 $ 165

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Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term.

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Cash and equivalents $ 71 $ — $ 71 $ — $ 49 $ — $ 49 $ —

Equity securities — — — — 223 223 — —

Global asset securities — — — — 39 39 — —

Fixed income securities — — — — 143 31 112 —

Total assets in fair value hierarchy 49 $ — $ 49 $ — 424 $ 293 $ 131 $ —

Assets measured at net asset value 676 667

Accrued investment income — 2

Due to brokers, net (pending trades with brokers) — ( 1 )

Total pension plan assets $ 747 $ 715

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Fair Level Level Level Fair Level Level Level

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Cash and equivalents $ 31 $ — $ 31 $ — $ 21 $ — $ 21 $ —

Equity securities — — — — 107 107 — —

Global asset securities — — — — 19 19 — —

Fixed income securities — — — — 69 15 54 —

Total assets in fair value hierarchy 21 $ — $ 21 $ — 204 $ 141 $ 63 $ —

Assets measured at net asset value 315 319

Accrued investment income — 1

Total pension plan assets $ 346 $ 340

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Cash and equivalents $ 32 $ — $ 32 $ — $ 22 $ — $ 22 $ —

Equity securities — — — — 93 93 — —

Global asset securities — — — — 16 16 — —

Fixed income securities — — — — 60 13 47 —

Total assets in fair value hierarchy 22 $ — $ 22 $ — 177 $ 122 $ 55 $ —

Assets measured at net asset value 295 281

Accrued investment income — 1

Total pension plan assets $ 327 $ 303

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Fixed income securities 52 52 — — 52 52 — —

Total assets in fair value hierarchy 80 $ 72 $ 8 $ — 64 $ 55 $ 9 $ —

Assets measured at net asset value — 19

Total OPEB plan assets $ 78 $ 71 $ 7 $ — $ 80 $ 72 $ 8 $ —

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Fixed income securities 40 40 — — 40 40 — —

Total assets in fair value hierarchy 59 $ 58 $ 1 $ — 43 $ 42 $ 1 $ —

Assets measured at net asset value — 18

Total OPEB plan assets $ 60 $ 57 $ 3 $ — $ 59 $ 58 $ 1 $ —

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WPL Value 1 2 3 Value 1 2 3

Cash and equivalents $ — $ — $ — $ — $ 1 $ — $ 1 $ —

Equity securities $ 2 $ 2 — — $ 2 $ 2 — —

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Total OPEB plan assets $ 14 $ 14 $ — $ — $ 13 $ 13 $ — $ —

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1 % of assets directly held in the plans at December 31, 2024 and 2023.

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1 % of the assets directly held in the plans at December 31, 2025 and 2024, respectively.

401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans).

Alliant Energy common stock directly held by participants represented 7 % and 8 % of total assets in the 401(k) savings plans at December 31, 2024 and 2023, respectively.

Alliant Energy common stock directly held by participants represented 7 % of total assets in the 401(k) savings plans at December 31, 2025 and 2024.

Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

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Alliant Energy IPL WPL

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A summary of the restricted stock units activity was as follows:

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2025 2024 2023

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Nonvested awards, December 31 313,384 54.06 289,148 51.85 234,259 52.58

Performance Shares (Net Income and Workforce Composition Metrics) (formerly granted as Performance Restricted Stock Units) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specific performance criteria, which currently is specified growth of cumulative consolidated net income from continuing operations, as well as a workforce composition metric.

Performance Shares (Net Income, Environmental and Workforce Composition Metrics) (certain awards formerly granted as Performance Restricted Stock Units) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specific performance criteria, which currently is specified growth of cumulative consolidated net income from continuing operations, as well as environmental and workforce composition metrics.

Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards.

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At December 31, 2025 and 2024, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $ 22 million and $ 23 million, respectively.

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ASSET RETIREMENT OBLIGATIONS

Recognized AROs relate to legal obligations for the removal, closure, dismantlement and management of several assets including, but not limited to, active and inactive ash landfills, ash ponds, wind farms, groundwater, solar facilities, above ground storage tanks and batteries.

Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls.

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MWhs Years MWhs Years Dths Years Gallons Years

Alliant Energy 1,682 2026 11,332 2026 140,731 2026-2032 — N/A

IPL 634 2026 4,482 2026 60,773 2026-2030 — N/A

WPL 1,048 2026 6,850 2026 79,958 2026-2032 — N/A

Alliant Energy 1,422 2025-2026 10,232 2025 147,894 2025-2032 2,520 2025

IPL 383 2025-2026 3,551 2025 61,489 2025-2030 — —

IPL 383 2025-2026 3,551 2025 61,489 2025-2030 — N/A

WPL 1,039 2025-2026 6,681 2025 86,405 2025-2032 2,520 2025

Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities.

At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):

At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):

Alliant Energy IPL WPL

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Non-current derivative liabilities 26 32 2 2 24 30

In 2024, Alliant Energy’s, IPL’s and WPL’s derivative liabilities decreased primarily due to settlements of natural gas contracts and higher natural gas prices.

Based on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

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B ased on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings.

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Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93 % on a portion of its variable-rate term loan borrowings.

In 2025, 2024 and 2023, $ 1 million, $ 4 million and $ 3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statements related to the interest rate swap.

In October 2025, AEC entered into a $ 300 million forward starting interest rate swap maturing in March 2028 to mitigate forecasted interest rate risk.

Under the terms of the swap, AEC exchanged a variable interest rate for a fixed interest rate of 3.10 % on a portion of its forecasted variable-rate term loan borrowings expected to be issued in 2026.

The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts.

As of both December 31, 2024 and 2023, $ 1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheets.

This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss.

As of both December 31, 2024 and 2023, accumulated other comprehensive income included $ 1 million of income related to the interest rate swap.

In 2024 and 2023, $ 4 million and $ 3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.

As of December 31, 2025, $ 1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet.

This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income.

As of December 31, 2025, accumulated other comprehensive income included $ 1 million of income related to the interest rate swap.

In 2025, there were no increases or reductions to interest expense recorded in Alliant Energy’s income statement related to the interest rate swap.

FAIR VALUE MEASUREMENTS

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Swap, option and physical forward commodity contracts were predominately at liquid trading points.

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FTRs were valued using auction prices and were categorized as Level 3.

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Long-term debt 3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170

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Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

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Beginning balance, January 1 $ 20 $ 19 $ 163 $ 216

Total net losses included in changes in net assets (realized/unrealized) ( 4 ) ( 3 ) — —

Total net gains (losses) included in changes in net assets (realized/unrealized) 5 ( 4 ) — —

Purchases 40 45 — —

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Ending balance, December 31 $ 25 $ 20 $ 126 $ 163

The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($ 4 ) ($ 3 ) $ — $ —

The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $ 5 ($ 4 ) $ — $ —

WPL Commodity Contract Derivative

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(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

Commodity Contracts - The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

Alliant Energy IPL WPL

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COMMITMENTS AND CONTINGENCIES

NOTE 16 (a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, and improvements at WPL’s natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility.

NOTE 16 (a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility.

At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $ 459 million, $ 302 million, and $ 155 million, respectively.

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NOTE 16 (b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers.

In addition, there are various purchase commitments associated with other goods and services.

At December 31, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):

At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):

Alliant Energy 2026 2027 2028 2029 2030 Thereafter Total

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Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2025 and 2024.

Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash.

As of December 31, 2024, IPL and WPL provided indemnifications associated with $ 193 million and $ 121 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law,

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including whether the related tax credits meet the qualification requirements.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash.

As of December 31, 2025, IPL and WPL provided indemnifications associated with $ 333 million and $ 266 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements.

Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers.

If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date.

As of December 31, 2025, IPL’s and WPL’s related guarantees were approximately $ 130 million and $ 55 million, respectively.

Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of December 31, 2025.

NOTE 16 (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations.

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District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa.

IPL has completed various requirements under the Consent Decree.

IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025.

IPL has completed all of the requirements under the Consent Decree.

Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

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CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including the CAA.

NOTE 16 (f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Minnesota, Illinois and Iowa.

NOTE 16 (f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Illinois and Iowa.

WPL provides retail electric and gas services and wholesale electric service in Wisconsin.

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In addition, as a result of a large customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or gas services.

Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price.

Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of generation and transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price.

Credit policies are maintained to mitigate credit risk.

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Refer to Notes 5(a) and 1 4 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.

NOTE 16 (g) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with FERC requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC and ATC.

In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88 % for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016.

In 2020, FERC issued orders in response to various rehearing requests and increased the base return on equity authorized for the MISO transmission owners from 9.88 % to 10.02 % for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016.

In 2022, the U.S.

Court of Appeals for the District of Columbia vacated FERC’s prior orders that established the base return on equity authorized

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for the MISO transmission owners and remanded the cases to FERC for further proceedings.

As a result of the 2022 court decision, Alliant Energy recorded a $ 6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the then-anticipated reduction in the base return on equity authorized for the MISO transmission owners.

In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98 %, and as a result, the MISO transmission owners will provide refunds based on the 9.98 % base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which did not result in any material impacts on Alliant Energy’s results of operations or financial condition in 2024.

Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs;

however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes.

NOTE 16 (g) Collective Bargaining Agreements - At December 31, 2025, employees covered by collective bargaining agreements represented 58 %, 74 % and 86 % of total employees of Alliant Energy, IPL and WPL, respectively.

In May 2026, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expires, representing 29 % and 86 % of total employees of Alliant Energy and WPL, respectively.

SEGMENTS OF BUSINESS

Alliant Energy - Alliant Energy’s reportable segments as of December 31, 2024 are:

Alliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:

• IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.

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Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other.

In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the Financial Accounting Standards Board’s accounting standard for improvements to reportable segment disclosures.

In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures.

Previously reported information for prior periods has been recast to conform with the current period presentation.

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Cost of gas sold expense 130 133 263 N/A 263

Asset valuation charge for IPL’s Lansing Generation Station 60 — 60 N/A 60

Other operation and maintenance expense 358 279 637 39 676

Other operation and maintenance expense (a) 373 306 679 61 740

Other segment items:

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Equity income from unconsolidated investments, net — ( 2 ) ( 2 ) ( 58 ) ( 60 )

Income tax expense (benefit) ( 129 ) 11 ( 118 ) 4 ( 114 )

Other (a) 5 34 39 5 44

Income tax benefit ( 127 ) ( 14 ) ( 141 ) ( 8 ) ( 149 )

Other (b) ( 4 ) 36 32 1 33

Net income (loss) 457 401 858 ( 48 ) 810

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Construction and acquisition expenditures 1,473 804 2,277 206 2,483

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Total Alliant

Reportable Energy

2023 (amounts may not foot due to rounding)

IPL WPL Segments Other Consolidated

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Cost of gas sold expense 123 101 224 N/A 224

Asset valuation charge for IPL’s Lansing Generating Station 60 — 60 N/A 60

Other operation and maintenance expense 358 279 637 39 676

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Income tax expense (benefit) ( 129 ) 11 ( 118 ) 4 ( 114 )

Other (a) 38 ( 27 ) 11 5 18

Other (b) 5 34 39 5 44

Net income (loss) 362 345 707 ( 17 ) 690

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Reportable Energy

2023 (amounts may not foot due to rounding)

IPL WPL Segments Other Consolidated

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Income tax expense (benefit) ( 58 ) 60 2 2 4

Other (a) 52 ( 2 ) 50 6 56

Net income 360 315 675 11 686

Other (b) 38 ( 27 ) 11 5 18

Net income (loss) 366 345 711 ( 8 ) 703

Total assets 10,489 9,634 20,123 1,114 21,237

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Construction and acquisition expenditures 712 1,019 1,731 123 1,854

(a) Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

(a) Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets.

Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $ 16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.

(b) Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

RELATED PARTIES

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As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO.

Corporate Services assigns such sales and purchases among IPL and WPL based on

Table of C o ntents

statements received from MISO.

Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO.

The amounts billed for services provided, sales credited and purchases were as follows (in millions):

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Compared sentence by sentence after normalising whitespace, quotation marks, case and digits, so re-formatting and restated figures do not read as changed language. Wording changes appear as one removal and one addition. The current filing and the prior one are authoritative.

What changed 10-K

Item 8. Financial Statements and Supplementary Data