Is My Portfolio Actually Diversified?
Updated ·2 min read·Reviewed by the StockTools.ai Research Team
- ▸Diversification is about how differently your holdings move, not how many you own.
- ▸Correlation runs from +1 (move in lockstep) through 0 (unrelated) to −1 (mirror opposites).
- ▸Two holdings correlated above ~0.8 give you little real diversification — you effectively own more of the same bet.
- ▸Correlations drift and tend to spike toward +1 in a crash, exactly when you were counting on them not to.
Ten stocks is not diversification
It is easy to feel diversified because you own a long list of tickers. But if all of them rise and fall together, you have not spread your risk — you have just spread your attention across many versions of the same bet. A portfolio of ten megacap tech names can be, in risk terms, close to owning one.
Real diversification comes from holding things that behave differently from one another. The tool for measuring "differently" is correlation, and it is the difference between a portfolio that looks diversified and one that actually is. Once you know how correlated your holdings are, a Monte Carlo simulation can show how that mix behaves across thousands of possible futures.
Check your holdings’ correlation
What correlation measures
Correlation is a single number, from +1 to −1, describing how two stocks’ day-to-day returns move together. A correlation near +1 means they rise and fall almost in lockstep; near 0 means their moves are essentially unrelated; near −1 means they tend to move in opposite directions. Two holdings correlated at 0.9 barely diversify each other — a bad day for one is almost always a bad day for the other.
The correlation matrix above computes this for every pair of tickers you enter and rolls it into a single diversification score. A high score means your holdings genuinely hedge each other; a low score means they are largely redundant. It is the fast answer to "am I actually diversified, or does it just look that way?"
The catch: correlation is not stable
The most important thing to know about correlation is that it moves. Two assets that look independent in calm markets can fall together in a panic, because in a broad selloff investors sell everything at once. Correlations across risky assets tend to spike toward +1 in exactly the crisis you were diversifying against — the moment you needed the diversification most.
That does not make diversification useless; it makes it worth checking with clear eyes. Treat any correlation figure as a backward-looking snapshot of recent behavior, not a promise. Assets that are structurally different — stocks versus high-quality bonds, for instance — hold up better in a crisis than a basket of stocks that merely looked uncorrelated day to day.
FAQ
What is a good correlation for diversification?
Lower is better. Holdings correlated above ~0.8 behave almost identically, so adding the second one barely reduces risk. Correlations near 0 or negative genuinely spread risk. The diversification score summarizes this across all your pairs into one number.
How many stocks do I need to be diversified?
There is no magic count — it is about correlation, not quantity. A handful of genuinely different holdings can be better diversified than dozens of similar ones. A broad index fund is diversified across hundreds of names in one holding; a pile of same-sector stocks is not, no matter how long the list.
Do bonds diversify a stock portfolio?
Historically, high-quality government bonds have often moved independently of — or opposite to — stocks, which is why the classic 60/40 portfolio exists. That relationship is not guaranteed (2022 saw both fall together), but structurally different asset classes tend to diversify better than stocks that merely appear uncorrelated.
Why did my "diversified" portfolio still crash?
Because correlations rise in a crisis. In a broad-market panic, things that normally move independently often fall together as investors sell everything at once. Day-to-day correlation understates how concentrated your risk becomes in exactly the worst moments.
Put it to work
Related guides
Sources & further reading
- ▸ Markowitz, H. (1952). Portfolio Selection. The Journal of Finance.
- ▸ Correlations computed from Databento EQUS end-of-day price history (Pearson, daily returns).
More to learn
Educational only — not financial advice. Concepts simplified for clarity; markets are messier than definitions.