What is S&P 500 Index (formerly Standard & Poor's 500 Index)

The S&P 500 Index (formerly Standard & Poor's 500 Index) is a market-capitalization-weighted index of the 500 largest U.S. publicly traded companies by market value, The index is widely regarded as the best single gauge of large-cap U.S. equities. Other common U.S. stock market benchmarks include the Dow Jones Industrial Average or Dow 30 and the Russell 2000 Index, which represents the small-cap index.

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Standard And Poor's 500 Index

BREAKING DOWN S&P 500 Index (formerly Standard & Poor's 500 Index)

The S&P 500 is one of the most widely quoted American indexes because it represents the largest publicly traded corporations in the U.S. The S&P 500 focuses on the U.S. market's large-cap sector and is also a float-weighted index, meaning company market capitalizations are adjusted by the number of shares available for public trading.

S&P 500 Versus Dow Jones Industrial Average

The S&P 500 is often the institutional investor's preferred index given its depth and breadth, while the Dow Jones Industrial Average has historically been associated with the retail investor's gauge of the U.S. stock market. Institutional investors perceive the S&P 500 as more representative of U.S. equity markets because it comprises more stocks across all sectors (500 versus the Dow's 30 Industrials).

Furthermore, the S&P 500 uses a market capitalization weighting method, giving a higher percentage allocation to companies with the largest market capitalizations, while the DJIA is a price-weighted index that gives companies with higher stock prices a higher index weighting. The market capitalization-weighting structure is more common than price-weighted method across U.S. indexes.

S&P Versus Russell Indexes

The S&P 500 is a member of a set of indexes created by the Standard & Poor's company. The Standard & Poor's set of indexes are like the Russell index family in that both are investable, market-capitalization-weighted (unless stated otherwise, like equal-weighted) indexes.

However, there are two large differences between the construction of the two families of indexes. One, Standard and Poor's chooses constituent companies via a committee, while Russell indexes use a formula to choose stocks to include. Second, there is no name overlap within S&P style indices (growth versus value), while Russell indexes will include the same company in both the "value" and "growth" style indexes.

Other S&P Indices

The S&P 500 is a member of the S&P Global 1200 family of indices. Other popular indices include the S&P MidCap 400, which represents the mid-cap range of companies and the S&P SmallCap 600, which represents small-cap companies. The S&P 500, S&P MidCap 400 and S&P SmallCap 600 combine to create a U.S. all-capitalization index known as the S&P Composite 1500.