What is the S&P 500?

Updated November 15, 2026 · examples use today’s data

The S&P 500 is an index of 500 of the largest US public companies, chosen by a committee at S&P Dow Jones Indices. It is the benchmark most investors, and most fund managers, are measured against.

How it is weighted

By market capitalization, so the biggest companies count most. Today the largest ten make up a large share of the whole index, led by Nvidia ($3.92 trillion), Microsoft and Apple.

Historical returns

Including dividends, the index has returned roughly 10% a year over the very long run, with painful drops along the way, including about −50% in 2008–09.

How to invest in it

Through a low-cost index fund or ETF. Most professional managers fail to beat it after fees over long periods.

Frequently asked questions

Is the S&P 500 the whole US market?

No, but its 500 companies make up roughly 80% of the US market’s total value.

How often do companies change?

The committee reviews the index every quarter and replaces companies after mergers or when they shrink.

Tools for this

What is an ETF?Return calculator

Keep learning

What is the P/E ratio and how do you use it?What is earnings per share (EPS)?What does TTM (trailing twelve months) mean?What is an ETF and how is it different from a stock?What is a dividend and what is dividend yield?What is compound interest and why does it matter so much?

Educational content, not investment advice. Figures in the examples come from company filings and market prices and update automatically.