The S&P 500 Index, or Standard & Poors 500 Index, is a market-capitalization-weighted index of 500 leading publicly traded companies in the U.S. . It is widely regarded as the best single gauge of large-cap U.S. equities and covers approximately 80% of available market capitalization. The index includes 500 leading companies from various sectors, such as technology, healthcare, and finance, and is a standard performance benchmark for many stocks, mutual funds, and ETFs, especially in the large-cap space. 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. . Companies must meet certain criteria to be eligible for the index, including having a market capitalization of at least $8.2 billion. The index is calculated by taking the sum of the market capitalizations of the 500 companies and dividing it by a divisor that is adjusted for changes in the indexs composition.