As of the end of September 2026, information technology made up 39.7% of the S&P 500, up about five points in a year, with the other ten sectors sharing barely over 60%.
The S&P 500 is not an even mix of everything. It is weighted by market value, so whichever companies rise most and grow biggest take up more of the index.
One sector, and still growing
Under GICS, the classification standard for US companies, information technology was 39.7% of the S&P 500 as of 30 September 2026, far ahead of the rest.
Financials came second at 11.4%, then communication services at 9.9%, health care at 9.3%, consumer discretionary at 8.6% and industrials at 8.0%.
Below that the sectors are small: consumer staples 4.4%, energy 3.4%, utilities 1.9%, and materials and real estate 1.7% each.
The weight was earned, not assigned
That 39.7% was not handed out by anyone. A year earlier tech sat at 34.7%, so it has added roughly five points in twelve months.
The reason is simple: tech stocks in that stretch outperformed the other sectors by a clear margin, their market values swelled, and their share of the index followed.
Put another way, buying the S&P 500 looks less like buying the whole US economy and more like buying a handful of tech companies, with four hundred-odd others along for the ride.
Why it matters
An index's weights are the market's own votes, not a designed balance. Anyone who thinks they own the whole American economy is actually holding a portfolio that leans ever harder on a few companies, and the risk is bigger than the name suggests.
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