The S&P 500 grew out of a railroad guide from 1860
America's best-known share index traces back to Henry Varnum Poor's 1860 handbook on railroads and canals. Today its 500 firms account for roughly 83 per cent of the value of all US public companies, and about $13 trillion in funds is set up to shadow it.
Two publishing lines merged to create it. Poor followed his railroad guide with a manual of American railroads in 1868. Separately, the Standard Statistics Company, founded in 1906 as a bureau, started rating mortgage bonds in 1923 and launched a weekly index of 233 US stocks. Three years later it added a 90-stock index calculated every day. The two firms combined in 1941 as Standard & Poor's, and on Monday, March 4, 1957, the index was widened to 500 companies under the name S&P 500 Stock Composite Index.
Trading products piled up around it. Vanguard launched the first retail mutual fund tracking the index on August 31, 1976. Futures arrived at the Chicago Mercantile Exchange in 1982 and options at the Chicago Board Options Exchange in 1983. From 1986 the value was recalculated every 15 seconds instead of once a minute. State Street's depositary receipts fund began trading in 1993, and the SPDR S&P 500 ETF Trust, with around $800 billion in assets, now has the highest daily volume of any fund tied to it.
A committee picks the members, and the index weights them by the value of their publicly traded shares, a method adopted in 2005. At the end of 2025 the constituents were worth over $61.1 trillion combined, ranging from $5.6 billion to $4.8 trillion each. About 72 per cent of their revenue comes from the United States. Firms that have raised dividends for more than 25 years running are dubbed Dividend Aristocrats.
Since 1926 its compound annual return with dividends has been about 9.8 per cent, or 6 per cent after inflation. It has risen in 70 per cent of years, though some years brought falls above 30 per cent.
Source: S&P 500
