The S&P 500 fell about 57% from its 2007 peak during the global financial crisis.
The broad U.S. index reached a closing high of 1,565.15 on 9 October 2007. It then declined as the housing downturn, mortgage-market losses, bank failures, and collapsing confidence spread through the financial system. The index reached a closing low of 676.53 on 9 March 2009.
The S&P 500 tracks 500 large U.S. companies, so its decline is often used as a broad measure of the crisis’s effect on American equities. The Dow and Nasdaq also suffered severe losses, but they contain different groups of companies and use different index methods.
The fall from the 2007 high to the 2009 low was approximately 57%, not exactly that number. Markets later recovered, although the economic damage extended well beyond stock prices.