The S&P 500 is a stock market index that tracks the performance of 500 of the largest publicly traded companies in the United States. Often called "the market," it represents about 80% of the total value of all stocks trading in the U.S. markets. With an aggregate market cap of over $61.1 trillion as of December 31, 2025, it is one of the most widely followed equity indices. The index includes stocks from various sectors, offering investors balanced exposure to different parts of the economy.
The S&P 500 is a capitalization-weighted index, meaning larger companies have a greater impact on its value. As of January 2026, the ten largest companies in the index included Nvidia, Apple, Microsoft, and Amazon, accounting for approximately 38% of the index's market capitalization. While the index is diversified, the technology sector holds a significant portion. The S&P 500 has historically provided an average annual return of roughly 10% since its launch in 1957. Investors cannot directly invest in the S&P 500 but can gain exposure through ETFs and mutual funds that mirror its performance.
