stocktools

Stock Split Calculator

See your share count and price after any N-for-M split — forward or reverse — and why position value doesn't change.

Your position & the split

Live tool
Split terms — "N-for-M" (N new shares for every M old shares)
or custom ↓
Forward split — 4-for-1
Split ratio (N ÷ M)4
Post-split shares400shares
Post-split price$12.50per share
Position value before$5,000.00
Position value after$5,000.00

Identical before and after. The share-count multiplier (N ÷ M) and the price multiplier (M ÷ N) cancel out — a split changes the denomination of your position, not its worth.

saves post-split shares (400) and price ($12.50)

How it works

A stock split is announced as "N-for-M": for every M shares you hold before the split, you hold N shares after it. When N is bigger than M — a 2-for-1 or 4-for-1 — it's a forward split: you end up with more shares at a lower price. When N is smaller than M — a 1-for-5 or 1-for-10 — it's a reverse split: fewer shares at a higher price.

Either way, the company's market value is unchanged, so the price moves exactly opposite to the share count and your total position value is mathematically identical before and after. That invariance is the core lesson: a split changes the denomination of your position, not its worth.

When the math doesn't land on a whole share — say 157 shares in a 1-for-10, which works out to 15.7 — brokers typically either credit the fractional share or pay "cash in lieu": a cash payment roughly equal to the fraction times the post-split price. Forward splits can create fractions too (a 3-for-2 on 5 shares leaves 7.5), so this tool handles fractional shares in both directions.

The formula

  • splitRatio = N ÷ M— the split ratio equals the new-share count N divided by the old-share count M of an "N-for-M" split. A 4-for-1 forward split has ratio 4; a 1-for-10 reverse split has ratio 0.1.
  • postSplitShares = shares × (N ÷ M) — your share count after the split equals your pre-split share count multiplied by the split ratio.
  • postSplitPrice = price × (M ÷ N) — the post-split share price equals the pre-split price multiplied by the inverse of the split ratio.
  • positionValue = shares × price = postSplitShares × postSplitPrice — identical before and after, because (N ÷ M) × (M ÷ N) = 1.
  • wholePostSplitShares = floor(postSplitShares) — the whole-share part of the post-split position, rounded down.
  • fractionalShareRemainder = postSplitShares − wholePostSplitShares — the fractional share left over (between 0 and 1).
  • cashInLieuEstimate = fractionalShareRemainder × postSplitPrice — the estimated cash payment if your broker pays "cash in lieu" for the fraction instead of crediting it.

Worked examples

Example A — forward split, 4-for-1

Inputs: 150 shares at $220.00 (N = 4, M = 1).

  1. splitRatio = 4 ÷ 1 = 4.
  2. postSplitShares = 150 × 4 = 600 shares.
  3. postSplitPrice = $220.00 × (1 ÷ 4) = $220.00 × 0.25 = $55.00 per share.
  4. Position value before = 150 × $220.00 = $33,000.00. After = 600 × $55.00 = $33,000.00. Identical — the split changed the share count and price, not the value.
  5. postSplitShares (600) is a whole number, so no fractional-share handling is needed.

Example B — reverse split, 1-for-10

Inputs: 157 shares at $0.48 (N = 1, M = 10).

  1. splitRatio = 1 ÷ 10 = 0.1.
  2. postSplitShares = 157 × 0.1 = 15.7 shares.
  3. postSplitPrice = $0.48 × (10 ÷ 1) = $4.80 per share.
  4. Position value before = 157 × $0.48 = $75.36. After = 15.7 × $4.80 = $75.36. Identical.
  5. wholePostSplitShares = floor(15.7) = 15. fractionalShareRemainder = 15.7 − 15 = 0.7 shares.
  6. cashInLieuEstimate = 0.7 × $4.80 = $3.36. If the broker pays cash in lieu, the holder ends with 15 shares worth 15 × $4.80 = $72.00 plus about $3.36 in cash — $72.00 + $3.36 = $75.36, still the original position value.

FAQ

Does a stock split change the value of my investment?

No. A split multiplies your share count by N÷M and divides the price by the same factor, so total value is mathematically unchanged. Any price move afterward comes from market reaction, not the split itself.

What is a reverse stock split?

A split where you end up with fewer, higher-priced shares — e.g., in a 1-for-10, every 10 shares become 1 share at 10× the price. Companies often use reverse splits to meet exchange minimum-price listing rules.

What happens to fractional shares in a reverse split?

If the math leaves a fraction (157 shares in a 1-for-10 → 15.7), brokers typically either credit the fractional share or pay "cash in lieu" — a cash payment equal to the fraction times the post-split price. Policies vary by broker.

Does a stock split change my cost basis?

Your total cost basis stays the same; the per-share basis is adjusted by the split ratio (halved in a 2-for-1, multiplied by 10 in a 1-for-10). Under US tax rules, the split itself is generally not a taxable event, though cash in lieu can be — rules vary and change (as of 2026).

Why do companies split their stock?

Forward splits usually aim to keep the per-share price in a range that feels accessible and keeps options contracts (100 shares each) affordable; reverse splits usually aim to lift a low share price, often for exchange compliance.

Do I need to do anything when a stock I own splits?

No action is required — brokers adjust share counts and prices automatically on the effective date. Investors typically just verify the new share count and update any saved cost-basis or profit calculations.

Continue your analysis

Your post-split shares and price travel with you once you confirm them above.

Recompute your average cost per share after the split →Project profit or loss from your post-split position →Measure your percentage gain — a split doesn't change it →

Disclaimer

Educational estimates only, not personalized advice. Cash-in-lieu amounts are broker-dependent estimates — the actual payment depends on the price at which the broker sells aggregated fractional shares. Cash in lieu received in a reverse split may be a taxable event under US tax law; tax rules vary and change (as of 2026), so consult a tax professional. US markets only.