If your biggest holding dropped 30% tomorrow, would you be okay?
Not "would you be annoyed." Would the things you've actually committed to survive it — the deposit, the retirement date, the ability to sleep through the week without selling at the bottom.
That question is a better test of concentration risk than any ratio, because you can answer it. Most people cannot tell you what percentage of their money sits in their single largest position. Almost everyone can tell you whether a 30% haircut on it would hurt.
Here's the rough shape of an answer anyway. As a general read, a largest holding under about 10% of your portfolio is unremarkable. Over about 20% is worth a serious look. But those lines move with the person: someone investing aggressively with a ten-year-plus horizon can sit nearer 30% without being reckless, while someone conservative who needs the money in three years should probably be tighter than 15%.
The rest of this is why that number sneaks up on people, what actually happens to individual companies over long stretches, and the constraint most articles skip — that selling to diversify comes with a tax bill attached.
Concentration almost always arrives as good news
Nobody decides to be concentrated.
It happens two ways, and both of them feel like winning. Either something you bought went up a lot and quietly grew into a bigger share of the pie, or you were paid in equity and it vested. In the first case, the position that made you money is also the position you trust most. In the second, the paperwork arrives labelled "compensation," not "exposure."
That's the whole reason concentration is systematically under-seen. Every other financial risk announces itself. Debt shows up as a payment. A thin buffer shows up the first time something breaks. Concentration shows up as a good year.
And it grows without you doing anything. You don't place a trade to become concentrated — the winner concentrates you by winning. Your holdings list looks identical to three years ago. The risk profile does not.
There's a worse version that's easy to miss: when the concentrated position is your employer's stock. Then your paycheck and your largest holding ride on the same company, and one bad event hits your income and your savings on the same day — exactly when you'd need one of them to be fine.
What actually happens to individual companies
The most useful data on this comes from J.P. Morgan's The Agony & the Ecstasy, a study of concentrated stock positions updated in March 2021. It looked at every company that was ever in the Russell 3000 index between 1980 and 2020.
More than 40% of them suffered what the authors call a catastrophic loss — defined as a 70% decline from peak that was never recovered. Across all sectors the figure was 44%. It varied a lot by industry: 14% in utilities, 59% in information technology, 65% in energy.
Two more numbers from the same study, same period. About 42% of stocks delivered negative absolute returns over their lifetime — meaning holding cash would have beaten them. And 66% underperformed the Russell 3000 index itself. Roughly 10% met the study's definition of a "megawinner."
The honest read of that data is not "individual stocks are bad." It's that the distribution is lopsided. A small number of companies carry almost all of the return, and there's no reliable way to know in advance which ones. That's perfectly workable when a single name is 5% of your money. It's a structurally different situation at 40%.
The bands, and what moves them
Thresholds get quoted like rules. They aren't. They're a starting read that gets adjusted for who's holding the position.
| Largest holding |
What it generally reads as |
What moves the line |
| Under ~10% |
Healthy. Concentration isn't the thing to look at in your portfolio. |
Very little. This band is comfortable for almost anyone. |
| ~10–20% |
Worth knowing about, not a problem in itself. |
A long horizon and genuine risk tolerance widen it; needing the money soon narrows it. |
| Over ~20% |
Flagged. Your result now depends materially on one company. |
Aggressive, 10-year-plus horizon can reasonably run nearer 30%. Conservative, short horizon should be nearer 15%. |
Three things move the band, and they're worth being honest with yourself about.
Time. A 30% drop with fifteen years left is a bad year inside a long sequence. The same drop eighteen months before you need the money is the outcome.
Actual risk tolerance, not stated risk tolerance. The version that counts is how you behaved the last time a position of yours fell hard. If you've never been through one, assume you're less tolerant than you think.
Whether the exposure doubles up. Employer stock is the obvious case — so is a large position in the same industry that employs you.
Why the question beats the percentage
The percentage tells you the exposure. The question tells you the consequence — and consequence is the thing you're actually deciding about.
A 30% drop in a single company is not a tail event, by the way. The study above found 44% of companies eventually fell more than twice that far and never came back. So the question isn't abstract stress-testing — it's rehearsing something reasonably likely.
Three follow-ups make it concrete:
- Does anything break? Name the actual commitments — a deposit, tuition, a retirement date — and check whether a 30% drop in this one position moves any of them.
- Would I sell? If the honest answer is yes, the position is larger than your conviction in it. That gap is the risk, more than the percentage is.
- Would I buy more at that price? If you'd want out at −30% rather than in, it's worth asking why this is your largest holding at today's price.
Question two is the one that catches people. Selling into a drop turns a paper decline into a permanent one — a different problem from concentration, but one that tends to arrive attached to it. We've written separately about what to do when the market drops.
The constraint most articles skip: tax
"Just diversify" is easy to write and expensive to do, because a concentrated position is usually concentrated for the happy reason. Selling it realizes a gain.
In the United States, the holding period decides how that gain is taxed. Per IRS Topic 409: hold an asset more than one year and the gain is long-term, taxed at 0%, 15%, or 20% federally depending on your taxable income. One year or less and it's short-term, taxed at ordinary income rates. That's a large gap decided by a calendar date.
Which is why the sensible version of reducing concentration is paced, not a single trade:
- Spread it across tax years rather than realizing everything in one, which can push you into a higher bracket in a single year.
- Check which lots are past the one-year mark. Different purchases have different clocks, and some of the position may be cheaper to sell than the rest.
- Use new money. This is the lever with no tax at all: stop adding to the position and direct new contributions elsewhere. The concentration falls as a share of the whole without a single sale. Slower, but free. Where that new money goes is its own question — how much should sit in stocks versus bonds is the usual next one.
The honest caveat: the right pace depends on your situation — your bracket, your state, other gains and losses that year, and whether the shares came from equity compensation with rules of its own. That's a conversation for a tax professional. None of this is tax advice, and the US rules above don't apply outside the US.
The concentration you can't see
A separate problem wears the same clothes: owning several funds that hold the same underlying companies. Your statement shows five line items and your money is in twenty names. Worth checking, because index-level concentration has risen sharply — the ten largest companies made up nearly 41% of the S&P 500 by the end of 2025, against roughly 19% at the end of 2015, with the single largest company alone at nearly 8% (RBC Wealth Management, January 2026). Owning three funds is not automatically diversification. We've unpacked how to measure the overlap in ETF overlap and fake diversification.
What this is not
This is not a case for selling anything.
Concentration isn't a mistake. It's a fact about a portfolio that carries a condition, and plenty of people carry it deliberately with their eyes open — a legitimate choice, and theirs to make. The failure mode isn't holding a big position. It's holding one without having priced what a bad month does to your plans.
That's also the honest scope of what a portfolio read can do. Ed connects to your brokerage to analyze what's there — it reads, it doesn't place trades, doesn't rebalance, and is not a registered investment advisor. What its portfolio health check gives you is the number you probably don't know: what share of your money sits in your single largest position, alongside what you're paying in fees and how much is sitting idle in cash.
The short version
Your largest holding has a percentage, and you should know it. Under about 10% is healthy, over about 20% deserves attention, and where your own line sits depends on your horizon, your real tolerance, and whether your income rides on the same company.
But the number is the diagnostic, not the decision. The decision comes from the question: if it dropped 30% tomorrow, would you be okay? If yes, you have a large position and an informed owner. If no, you have something worth working on slowly, in a way that respects the tax bill.
Find out what your largest position actually is
Ed's check-up reads your real situation — including how much of your money depends on one company — in a few minutes, with no jargon and nothing to sell you.
Start at edwealth.ai/check-up, or download the app on App Store or Google Play.
Money at peace. Wealth in motion.
Ed Wealth is a research and self-reflection tool, not a registered investment advisor. Nothing here is financial, investment, or tax advice. All decisions are yours.
Sources
- J.P. Morgan, Eye on the Market Special Edition: The Agony & the Ecstasy — The Risks and Rewards of a Concentrated Stock Position, March 15, 2021 — assets.jpmprivatebank.com/content/dam/jpm-pb-aem/global/en/documents/eotm/agony-ecstasy-2021.pdf
- Internal Revenue Service, Topic no. 409, Capital gains and losses — irs.gov/taxtopics/tc409
- RBC Wealth Management, The "Great Narrowing": S&P 500 concentration, January 22, 2026 — rbcwealthmanagement.com/en-us/insights/the-great-narrowing-sp-500-concentration
- Lord Abbett, Equities: Time for a Conversation About Stock Market Concentration, February 4, 2026 — lordabbett.com
