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As of this writing, the S&P 500 ( ^GSPC +0.73% ) has climbed around 12% in 2026, not counting dividends. Anyone who owns a fund tracking the index has had a good nine months. But the average company in the index hasn't kept up.
The S&P 500 Equal Weight Index, which includes the same companies but gives each the same weight, has gained around 9% over that time. It's a decent stand-in for how the average stock in the index has done. A gap of around 3 percentage points may not look like much.
But that shows a small group of stocks carried much of the index's gain -- and, I'd argue, a different group than many index fund owners might expect. Image source: Getty Images. A September split For most of 2026, the average stock was ahead.
At the end of August, the equal-weight index was up around 14% for the year, compared to about 12% for its market-value-weighted sibling. It held the lead until the middle of September. Then the two split apart.
In September, the S&P 500 dipped around 0.5%, but the equal-weight index slid about 5%. Around three-quarters of the stocks in the S&P 500 dropped over the month. Meanwhile, gains in a few of the index's biggest companies, like Apple ( AAPL +1.02% ) and Nvidia ( NVDA +1.34% ) , hid the weakness in most of the rest.
The typical stock looks even weaker than the 9% number suggests. By my count, only about half of the companies that were in the index at the start of 2026 are up as of this writing. Four stocks did half the work Going into 2026, AI chip leader Nvidia made up about 7.8% of the Vanguard S&P 500 ETF , and Apple made up about 6.9%, according to the fund's annual report -- together, almost 15% of the money.
Both stocks have done well since. Nvidia shares have climbed about 24% this year, to roughly $231 as of this writing, and Apple's have risen about 22%. With weights that big, gains like these move the whole index.
The other two began far smaller. Micron Technology ( MU -2.05% ) and Advanced Micro Devices ( AMD +2.95% ) were each a bit over half a percent of the fund. But Micron's stock has nearly quadrupled in 2026, up around 285%, and AMD's has gained about 188%.
The memory chipmaker's business changed almost as fast, too. Its revenue more than tripled in fiscal 2026 (the year ended Sept. 3, 2026), to around $133 billion. Multiply each stock's starting weight by its gain, and these four total about 6 points of the S&P 500's 12% rise.
Put another way, of the roughly $1,200 that $10,000 in an S&P 500 fund has made from higher share prices this year, about $600 came from Nvidia , Apple, Micron, and AMD. The rest of the index, about 84% of the money in January, rose about 7% together. Of course, not every giant helped.
Tesla shares have dropped around 21% in 2026, and Microsoft has gained only about 6%. Tesla and Microsoft both began the year among the index's 10 largest holdings, and both lagged the average stock, which probably kept the gap from being wider. What does this mean for index fund owners?
Mainly, it means an S&P 500 fund did its job. It held this year's winners in proportion to their size, and as they rose, they automatically made up more of the fund. By my math, Micron's weight in the index has more than tripled since January, and AMD's has more than doubled.
That works in reverse, too. If the chip stocks behind this year's gain give some of it back, an S&P 500 fund might feel it more than the average stock would. After all, a stock that almost quadrupled in nine months could drop a lot, even if the business stays strong.
Index S&P 500 Index Today's Change ( 0.73 %) + 56.27 Index Level 7,722.72 Yes, a 3-point gap can close fast. The equal-weight index led as recently as mid-September. But for now, this year's 12% gain rests heavily on four stocks, three of them chipmakers.
I don't see that as a reason to sell an S&P 500 index fund or trade it for something else. Owning the biggest winners at their full size is how the index is built. But I'd keep in mind that much of the fund's next move could depend on how a few chip stocks do, and not just on how the average company does.
Source: The Motley Fool
