Ten Stocks, 40% of the Market: You're More Concentrated Than You Think

The index stopped being a hedge against your stock

The pitch for an S&P 500 fund has always been the same: own 500 companies and no single one can sink you. In late October 2026 that pitch needs an asterisk. Just ten stocks now account for nearly 40% of the index's value, up from about 17% in 2015 and the highest share since the mid-1960s. Nvidia alone is about 8.4% of the Vanguard S&P 500 ETF.

Those ten also did most of the work this year. Through Oct. 15 they added $4.93 trillion of market value, about 59% of the entire index's gain. And when they wobble, the whole market wobbles with them: in one mid-October week the Nasdaq 100 fell 5.5% as investors questioned how quickly the $1 trillion-a-year AI build-out will pay back.

Your stock, plus the index's version of your stock

Most people with a concentrated position also own index funds, often bought as the "safe" part of the portfolio. But if your stock is one of the ten, the fund quietly buys you more of it, and more of its neighbors in the same AI trade.

Take a long-tenured engineer with $3 million in Nvidia and $2 million in an S&P 500 fund. The fund holds about 8.4% Nvidia, another $168,000. Real Nvidia exposure is about $3.17 million, or 63% of the $5 million. Count the rest of the top ten and roughly 76% of this "diversified" portfolio rides on about a dozen companies that tend to rise and fall together.

None of this means the index is broken or the stock is a bad holding. It means the usual comfort ("the rest of my money is diversified") is weaker than it was ten years ago, at exactly the moment the market is debating whether the leaders are priced for perfection.

Why one great stock is a fortune and a risk at once

Arizona State's Hendrik Bessembinder has spent a decade on one uncomfortable question: do individual stocks beat cash? His update, covering roughly 30,000 US stocks from 1926 to 2025, finds that fewer than half posted positive lifetime returns and just 41.17% beat one-month Treasury bills. Only 46 companies account for half of the $91 trillion of wealth the market created, more concentrated than his 2017 finding of 89.

Read the chart both ways. If you own one of the rare compounders, your concentration is the reason you are wealthy, and selling it all to buy the index means paying tax to own more of the stocks that historically lag cash. But you never know in advance which side of the line a stock will finish on. J.P. Morgan's long-running study of concentrated positions found that about 40% of Russell 3000 stocks since 1980 suffered a 70%+ fall from their peak and never recovered.

That is the case for a middle path: keep the position you believe in, but stop relying on its price alone to fund your life.

How much of your net worth rides on a dozen companies?

Enter your single-stock position and what you hold in index funds. The tool assumes your stock is one of the index's ten largest and that the top ten are about 40% of the fund.

Keep the compounder, change what it does for you

Most concentration advice offers two doors: sell and pay the tax, or hold and hope. Embark is built for the room between them.

• No sale, no tax at contribution. You contribute shares in kind to an Embark SPV under IRC §721. Your basis carries over, so the gain is deferred rather than triggered.
• The position goes to work. Embark's team runs income strategies on the contributed stock that target 10%+ a year, distributed and reported on a K-1.
• Diversify on your schedule. Income you receive can fund the index, bonds or a direct indexing account, so diversification comes from cash flow instead of a taxable sale.

The trade-offs are real: the stock's downside stays with you, income varies with market conditions and can trail the stock in a sharp rally, and the offering is for verified accredited investors only. If you would rather keep shares in your own brokerage account with no tax deferral, Income+ runs similar strategies there.

Three things to do before the next Dispatch

• Add up your look-through exposure. Single stock, plus index funds, plus any RSUs still vesting. Write the percentage down.
• Set your trigger now, not mid-drop. Decide in advance what you would do if the stock fell 25%: sell some, hedge, or make it pay. Decisions made during a sell-off are rarely the good ones.
• Price the tax. Know what a full sale would cost before anyone tells you to diversify. The calculator above takes a minute.

Next, No. 03 (Oct. 31): the 10-year Treasury yield is near 5%. Should you sell your stock to buy bonds? We run the after-tax math.

Questions readers ask

What percentage of the S&P 500 is in the top 10 stocks?

Nearly 40% as of late October 2026, according to The Motley Fool's analysis of index weights. That is up from about 17% in 2015 and the highest level since the mid-1960s. Nvidia alone was about 8.4% of the Vanguard S&P 500 ETF.

Is it bad to hold an S&P 500 fund and a large single stock at the same time?

Not automatically, but the exposures stack. If your stock is also a top index holding, the index fund adds more of the same company and the same sector. Add the two together to see your real concentration.

How much of a portfolio in one stock is too much?

Many wealth managers treat 10% to 20% of liquid net worth in a single stock as the point where the risk deserves a written plan. The right number depends on your other assets, your spending needs and how much of your salary also depends on that company.

Do most stocks beat cash over the long run?

No. Hendrik Bessembinder's study of about 30,000 US stocks from 1926 to 2025 found that just 41.17% beat one-month Treasury bills over their lifetimes, and 46 companies accounted for half of the $91 trillion in wealth created.

How does Embark help with a concentrated position?

Embark accepts appreciated stock as an in-kind §721 contribution to a partnership SPV, so no tax is due at contribution, and runs income strategies on the position that target 10%+ a year. Income is a target, not a guarantee, and offerings are for verified accredited investors.