The S&P 500 lost about 57% from its 2007 peak to its 2009 financial-crisis low.
The index reached a closing high of 1,565.15 on October 9, 2007, before falling to 676.53 on March 9, 2009. The decline was driven by the collapse of the U.S. housing boom, losses on mortgage-related securities, failures and rescues involving financial institutions, and a worldwide contraction in credit.
A fall of about 57% is measured from the closing peak to the closing trough. Intraday figures, different dates, and different market indexes can produce slightly different percentages, which explains why sources may round the loss differently.
The S&P 500 tracks large U.S. companies across many industries, so its decline represented more than a technology-sector collapse. It was considerably larger than the Dow’s 1987 one-day percentage fall, but it unfolded over roughly seventeen months rather than a single session.