Stats › Concentration and breadth › Index turnover

How long companies stay in the S&P 500

Concentration/turnover · Innosight and Apollo · 2 sources · data as of 31 Jul 2026

Membership of the S&P 500 isn't permanent. Companies get added when they grow into the criteria and dropped when they're bought, when they shrink, or when they stop meeting one of the tests. So the five hundred companies in the index today are not the five hundred that were in it when you started, and over a long enough holding period they're not even mostly the same companies.

This page is about how fast that happens. The average company now stays in for about fifteen years, and that number has been falling for decades. The page covers where that figure comes from, the two competing explanations for why it keeps dropping, and what it means for anyone who owns an index fund and thinks of it as a passive holding. I wanted this written down because the way index investing gets described and the way it actually works are two different things. Nobody sold you a strategy that continuously sells what's shrinking and buys what's already grown. That's what you own though, and it's worth understanding on its own terms rather than through the marketing.

Fair warning that this is a thin page by design. The commonly repeated figures for tenure in earlier decades, the ones you'll see in every slide deck, couldn't be verified against the original research, so they aren't here. What is here is sourced and linked at the bottom. If you need the historical comparison, go to the primary research rather than to a secondary summary of it.