What US stock market index tracks 500 large companies?

The S&P 500 is the U.S. stock market index that tracks 500 leading large-cap companies. It is maintained by S&P Dow Jones Indices and is widely used as a benchmark for the American equity market.

The index is market-capitalization weighted, with adjustments for shares available to public investors. That means larger companies generally have a greater effect on its movements than smaller constituents. The index covers roughly 80% of the available U.S. equity-market capitalization.

Despite its name, the S&P 500 does not always contain exactly 500 stocks. Some companies issue multiple share classes, so the index can hold more than 500 individual securities while representing 500 companies. Its components are selected using criteria that include size, liquidity, profitability, and sector representation.

A common mix-up is confusing it with the Dow Jones Industrial Average, which contains only 30 companies, or the Russell 2000, which focuses on smaller companies. The S&P 500 is a broad large-cap benchmark, not a complete measure of every U.S. stock.