Crypto Portfolio Concentration Risk: How to Measure It (HHI Explained)

Concentration risk hides behind a long coin list. Measure it with the HHI and effective number of holdings, using a worked eight-coin example and thresholds.

Owning eight coins feels diversified. Whether it is depends almost entirely on how the money is split among them. This guide shows how to put a single number on that split, what the number means, and why the largest position matters more than the length of the list.

What is concentration risk in a crypto portfolio?

FINRA defines concentration risk as “the risk of amplified losses that may occur from having a large portion of your holdings in a particular investment, asset class or market segment relative to your overall portfolio.” In crypto it tends to arrive in one of three ways.

• Performance drift. One coin rallies and quietly grows from a quarter of the portfolio to half of it.
• Deliberate conviction. You overweight the asset you believe in most.
• Hidden overlap. Several holdings share the same driver, such as tokens from one ecosystem or a coin plus its wrapped version.

The first is the easiest to miss, because nothing about it requires a decision. That is why measuring beats eyeballing.

Example: In the eight-coin portfolio below, a 50% rally in Coin A with everything else flat would lift its weight from 55% to 64.7% and cut effective holdings from 2.9 to 2.3, without a single trade.

How does the HHI measure concentration?

The Herfindahl-Hirschman Index is best known from antitrust work, where the U.S. Department of Justice uses it to gauge how concentrated a market is. The recipe works just as well for a portfolio:

1. Divide each holding’s value by the total to get its weight.
2. Square each weight.
3. Add the squares. That sum is the HHI.

The result runs from near 0 (many tiny positions) to 1 (everything in one coin). Its reciprocal, 1 ÷ HHI, is the effective number of holdings: how many equal-sized positions would produce the same concentration.

Antitrust agencies quote HHI on a 10,000-point scale, so 0.20 becomes 2,000 points. Under the 2023 federal merger guidelines, a market above 1,800 points counts as highly concentrated. For a portfolio, 1,800 points means about 5.6 effective holdings, a handy reference even though a portfolio is not a market.

All four portfolios in the chart hold exactly five coins. Only the weights differ, and the effective number falls from 5.0 to 1.5 as the top coin grows.

Worked example: an eight-coin portfolio that behaves like three

Suppose you hold eight coins worth $12,000. The values are hypothetical.

The squares add up to an HHI of 0.342, about 3,420 points. The effective number of holdings is 1 ÷ 0.342 = 2.9. Eight tickers, but the concentration of fewer than three equal positions.

The last column is the useful one. Each holding’s share of the HHI is its squared weight divided by the total, and Coin A supplies 88.4% of it. Squaring punishes big weights: Coin A is 22 times the size of Coin H, yet it contributes about 484 times as much to the index.

Why adding more coins barely helps

Suppose you add a ninth coin with $600 of new money. The total becomes $12,600, Coin A’s weight falls to 52.4%, and effective holdings rise from 2.92 to 3.20. Putting the same $600 into Coin H instead would lift the figure to 3.17, so the new ticker itself adds only about 0.02. Nearly all of the improvement came from diluting Coin A.

That points to a hard ceiling. Because every squared weight is positive, the HHI can never be smaller than the square of your largest weight. So:

Effective holdings ≤ 1 ÷ (largest weight)²

With Coin A at 55%, the ceiling is 1 ÷ 0.3025 = 3.3, however many small coins you add. Run it backward and you get a quick decision table.

These are ceilings, not targets. Reaching them also requires the remaining weight to be spread fairly evenly. If the top weight keeps drifting upward, calendar and threshold rebalancing are two ways to decide when to act.

How should you read your HHI?

The eight-coin example lands in the “2 to 3” row. None of these bands is a rule you must follow. They simply tell you where concentration starts to dominate the outcome, and they feed the concentration vital sign in our guide to a healthy crypto portfolio.

How to calculate HHI in a spreadsheet

List each holding’s current value in column A, then put its weight in column B as the value divided by the total. With eight holdings in rows 2 to 9, =SUMSQ(B2:B9) returns the HHI and =1/SUMSQ(B2:B9) returns effective holdings. Or enter the same values in our portfolio health check, which computes both along with the largest weight.

Tip: Merge duplicates before you calculate. The same coin held on two exchanges, or a coin and its wrapped version, is one position, not two.

Common mistakes when measuring concentration

• Counting stablecoins as diversification. A portfolio split 50/50 between one coin and a stablecoin has two effective holdings overall, but a single coin’s worth of crypto risk. Compute HHI with and without stablecoins, and see how to size a stablecoin allocation for what the cash sleeve is actually for.
• Measuring once. Weights drift with prices, so an HHI from last quarter can be badly out of date after a rally.
• Ignoring correlation. HHI treats every coin as a separate bet. If most of your coins tend to move together, the real diversification is lower still; crypto correlation explains how to check.
• Chasing a big count. The diversification math on how many coins to hold shows how quickly extra coins stop reducing risk.

The bottom line

Concentration risk is about weights, not tickers. Square your weights, add them up, and take the reciprocal to see how many equal positions your portfolio really behaves like. If one holding dominates the HHI, no number of small additions will change the picture much; only the size of that top weight will.

This content is for education only and is not financial, investment, tax or legal advice. Crypto assets are volatile and you can lose money. Examples use hypothetical numbers. See our disclaimer and editorial policy.