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Glossary

The S&P 500

A stock market index that measures the value of the shares of 500 large companies listed on US stock exchanges and reports it as a single number.

Updated September 15, 2026

The S&P 500 is a stock market index: a published list of investments plus a rule for turning their prices into one number. It measures the value of the shares of 500 large companies listed on US stock exchanges, chosen by a committee at S&P Dow Jones Indices, which calculates and publishes it. Larger companies count for more, so the biggest ones move the number most.

You cannot put money into the index itself, because it is only a measuring stick. Some funds hold the index's shares in similar proportions, aiming to match its return less their costs. Such funds carry the full risk of owning shares in large US companies: the index fell by about 37 percent in 2008 including cash payouts to shareholders, and fell again in 2022. It leaves out smaller US companies and foreign markets.

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How this definition was made

  • Written by an AI model (Claude) following Teloria's editorial standard.
  • Every factual claim was checked by a separate AI fact-check against official US government and regulator sources.

Official sources consulted

  • investor.gov · /introduction-investing/investing-basics/investment-products/mutual-funds-and-exchange-traded-4
  • sec.gov · /Archives/edgar/data/826686/000119312526048949/d93762d497.htm
  • sec.gov · /Archives/edgar/data/918294/000174177321001013/c485bpos.htm
  • dol.gov · /sites/dolgov/files/EBSA/about-ebsa/about-us/erisa-advisory-council/2024-qdia-pollock-witness-statement-0910.pdf
  • sec.gov · /Archives/edgar/data/0000795259/000110465909015505/a08-30160_1ncsr.htm
  • sec.gov · /Archives/edgar/data/826686/000119312513480743/d640467d497k.htm
  • investor.gov · /introduction-investing/general-resources/news-alerts/alerts-bulletins/investor-bulletins-26
  • sec.gov · /Archives/edgar/data/0001091439/000095015209002366/l35240anvcsr.htm
  • sec.gov · /Archives/edgar/data/722574/000072257423000116/filing5685.htm