The S&P 500, also known as the Standard & Poor's 500, is a stock market index that tracks the performance of 500 of the largest publicly traded companies in the United States. Often considered a bellwether for U.S. stocks, it represents approximately 80% of the total market capitalization of the U.S. stock market. With an aggregate market cap exceeding $61.1 trillion as of December 31, 2025, the S&P 500 is one of the most widely followed equity indices.
The index is capitalization-weighted, meaning that larger companies have a greater impact on the index's value. As of January 2026, the ten largest components include Nvidia, Alphabet, Apple, Microsoft, Amazon, Broadcom, Meta Platforms, Tesla, Berkshire Hathaway, and Eli Lilly. Investors often use the S&P 500 as a benchmark for their own portfolios and to gauge the overall health of the U.S. stock market and economy. While you cannot invest directly in the S&P 500, you can invest in index funds or ETFs that track its performance. Since its launch in 1957, the S&P 500 has provided an average return of about 10% annually.