The S&P 500's IT sector weighs 39.7%, but two classification changes in 2018 and 2023 moved Google, Meta and Visa out; the author estimates it would be about 55% without them.
In the S&P 500, the Global Industry Classification Standard (GICS) decides which sector each listed company belongs to: information technology, financials, communication services and so on. In October 2026 the IT sector carried a 39.7% weight, more than three times the 11.4% of second-placed financials.
But the sector was meant to be bigger. In 2018, when its weight had passed 25%, the GICS committee moved a batch of internet companies, Google and Meta among them, into communication services. The ETF VGT, which tracks the sector, stopped holding them.
In 2023, with the weight again above 27%, the committee moved fintech firms such as Visa, Mastercard and PayPal into financials, and VGT lost those holdings too.
The fine print matters more than the number
The author estimates that without the 2018 and 2023 changes, the IT weight would sit near 55%.
Sector boundaries are rules set by a committee, not borders companies grew up inside, so before comparing sector weights across years, check whether the rules changed.
In short, before reading a sector weight, look at the list: which company sits in which box is something a committee redraws, year by year.
Why it matters
Sector weights are often read as the market's bet on tech, but the number also moves when the rulebook does. Before comparing years or judging where money is flowing, check who sits in which box.
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