How Much of Your Portfolio in One Stock Is Too Much?
"Diversified" is a word a lot of portfolios claim and few actually earn. Owning 20 different tickers doesn't mean much if one of them is 60% of your money. This page walks through the actual math — the Herfindahl-Hirschman Index (HHI) and single-holding weight — that Zyvo runs automatically against your real portfolio, so you can work out roughly where you stand before ever connecting an account.
Calculate your own concentration score
Enter each position as a percent of your total portfolio — or any consistent unit, since the math normalizes automatically (the same way Zyvo's own engine does it). Leave rows blank if you have fewer than five positions.
Calculated entirely in your browser using the formula and thresholds explained below — nothing you enter here is sent anywhere.
What HHI actually measures
The Herfindahl-Hirschman Index is a standard concentration measure borrowed from antitrust economics, applied here to portfolio weights instead of market share. The calculation: take each position's percentage of your total portfolio, square it, add up every position's squared weight, then multiply by 10,000. Squaring is what makes it different from just counting positions — a position twice as large contributes four times as much to the score, not twice as much, so a few oversized positions move the number far more than a long tail of small ones. This is exactly what the calculator above just did with your numbers.
Worked examples
| Portfolio shape | HHI score | Zyvo's label |
|---|---|---|
| 10 equal positions (10% each) | 1,000 | Well diversified |
| 5 equal positions (20% each) | 2,000 | Moderate concentration |
| 4 equal positions (25% each) | 2,500 | High concentration |
| 40% / 20% / 15% / 15% / 10% split | 2,550 | High concentration |
| One position, 100% of portfolio | 10,000 | High concentration |
The third row is worth sitting with: a portfolio split perfectly evenly across just four stocks already scores 2,500 — the exact point where Zyvo's own concentration alert starts firing. That's not a bug in the math; it's the actual, somewhat uncomfortable implication of squaring the weights. Four is fewer positions than most people picture when they hear "high concentration." Try it yourself above: four 25% rows will land you exactly there.
Zyvo's exact thresholds
Zyvo computes HHI on every dashboard load and labels the result the same way used above: under 1,500 is well diversified, 1,500–2,499 is moderate concentration, and 2,500 or higher is high concentration — which is also the point where Zyvo's in-app alert actually triggers. Below 2,500, HHI is shown for reference but doesn't raise a warning on its own.
The single-holding check: a second, simpler number
HHI is powerful but not always intuitive at a glance, so Zyvo separately tracks a plainer number: what percentage of your total portfolio value sits in your single largest holding. A warning appears at 25%, escalating to critical at 40%. Unlike HHI, this ignores how everything else is distributed — it exists specifically to catch the case where one position has quietly become most of your risk, even if the rest of the portfolio looks reasonably spread out. Both thresholds are adjustable in Zyvo's alert preferences, and a dismissed alert re-checks itself if that position's weight changes meaningfully rather than staying silenced forever.
Why "number of stocks" is the wrong question
A 20-stock portfolio where one position is 60% of the total is more concentrated by HHI than a 5-stock portfolio split evenly — the position count tells you almost nothing on its own. For the fuller picture of why this happens gradually (winners compounding faster than the rest of a portfolio is one common cause) and what tends to trigger it, see Portfolio Concentration Risk: Why "Diversified" Often Isn't.
See your own number
Working this out by hand for a real portfolio — correctly weighting positions held across multiple brokers, keeping it current as prices move — gets tedious fast. Zyvo calculates both HHI and single-holding weight automatically from your actual positions, refreshed as prices update, with no spreadsheet required.
Frequently asked
How much of my portfolio in one stock is too much?
There's no single universal number, but Zyvo's own alert thresholds are a reasonable reference point: a warning at 25% of total portfolio value in one holding, escalating to critical at 40%. Both are adjustable — some investors are comfortable with more concentration than others, especially in a stock they understand deeply.
What is a good HHI score for a stock portfolio?
Using the standard 0–10,000 scale, Zyvo treats under 1,500 as well diversified, 1,500–2,499 as moderate concentration, and 2,500 or above as high concentration. For reference, a portfolio split evenly across exactly 4 positions already scores 2,500.
Is HHI the same as counting how many stocks I own?
No, and that's the point of using it. A 20-stock portfolio where one position is 60% of the total is more concentrated by HHI than a 5-stock portfolio split evenly — HHI weights by dollar size, not by how many tickers appear on your statement.
Does Zyvo calculate this automatically?
Yes. Zyvo computes your portfolio's HHI and single-holding weight automatically from your actual positions and raises an in-app alert when either crosses its threshold — no manual calculation required.
See your actual HHI and single-holding weight — no signup required.
Open a real sample portfolio and check the Risk & Allocation view for yourself.
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