The S&P 500 (Standard and Poor's 500) is a stock market index tracking the stock performance of 500 companies listed on stock exchanges in the United States that are considered to have large market capitalizations. The S&P 500 is a subset of the S&P 1500. It is maintained by S&P Dow Jones Indices and its components are selected by a committee. For a list of the criteria for addition to the index, see S&P 1500 § Selection criteria.
The index is a public-float-weighted/capitalization-weighted index. The index includes approximately 83% of the total market capitalization of U.S. public companies, with an aggregate market capitalization of more than $61.1 trillion as of December 31, 2025. The median market capitalization of the components of the index is $41.8 billion and components range in market capitalization from $5.6 billion to $4.8 trillion.
Products linked to the S&P 500 include index funds (exchange-traded funds/ETFs and mutual funds) as well as derivatives (options and futures contracts), which are available for trading in many countries with the goal of replicating the performance of the index. Also available are modified index funds; they replicate the performance of the index with modifications such as the use of covered call strategies, equal weighting, performance buffers, leverage, inclusion of only growth or value stocks, or exclusion of certain sectors, all with the goal of changing the risk/return and yield. The SPDR S&P 500 ETF Trust, with approximately $800 billion in assets, has the highest average daily volume of all S&P 500 ETFs. In total, there was approximately $13 trillion in assets tracking the index as of December 31, 2024.
The component companies that have increased their dividends over 25 consecutive years are known as the S&P 500 Dividend Aristocrats. Companies in the S&P 500 derive a collective 72% of revenues from the United States and 28% from other countries. The index is one of the factors in the computation of the Conference Board Leading Economic Index, which is used to forecast the direction of the economy. The index is associated with many ticker symbols, including ^GSPC,. INX, and SPX, depending on market or website.
Contents
History
In 1860, Henry Varnum Poor published the History of Railroads and Canals in the United States, a reference guide to the railroad industry for investors; in 1868 he published the book's follow-up, Poor's Manual of the Railroads of the United States. In 1923, Standard Statistics Company (founded in 1906 as the Standard Statistics Bureau) began rating mortgage bonds and developed its first stock market index consisting of the stocks of 233 U.S. companies, computed weekly. Three years later, it developed a 90-stock index, computed daily. In 1941, Poor's publishing company merged with Standard Statistics Company to form Standard & Poor's.
On Monday, March 4, 1957, the index was expanded to its current extent of 500 companies and was renamed the S&P 500 Stock Composite Index. In 1962, Ultronic Systems became the compiler of the S&P indices including the S&P 500 Stock Composite Index, the 425 Stock Industrial Index, the 50 Stock Utility Index, and the 25 Stock Rail Index. On August 31, 1976, The Vanguard Group offered the first mutual fund to retail investors that tracked the index. On April 21, 1982, the Chicago Mercantile Exchange began trading futures based on the index. On July 1, 1983, the Chicago Board Options Exchange began trading options based on the index. Beginning in 1986, the index value was updated every 15 seconds, or 1,559 times per trading day, with price updates disseminated by Reuters. Prior to this, it had been updated once every minute.
On January 22, 1993, the Standard & Poor's Depositary Receipts exchange-traded fund issued by State Street Corporation began trading. On September 9, 1997, CME Group introduced the S&P E-mini futures contract. In 2005, the index transitioned to a public float-adjusted capitalization-weighting. Friday, September 17, 2021, was the final trading date for the original SP big contract which began trading in 1982.
Performance
Since its inception in 1926, the index's compound annual growth rate—including dividends—has been approximately 9.8% (6% after inflation), with the standard deviation of the return, calculated on a monthly basis, over the same time period being 20.81%. While the index has declined in several years by over 30%, it has posted annual increases 70% of the time, with 5% of all trading days resulting in record highs.