The S&P 500 fell approximately 56.8% from its 2007 peak to its 2009 low during the global financial crisis.
The index reached a closing high of 1,565.15 on 9 October 2007. It later reached a closing low of 676.53 on 9 March 2009, producing a decline of about 56.8% between those closing levels.
The fall occurred amid a broad financial crisis involving the collapse of the United States housing bubble, losses on mortgage-related securities, failures and rescues of financial institutions, and severe tightening of credit. The crisis spread internationally through interconnected banks and markets.
The 56.8% figure describes the S&P 500’s peak-to-trough decline, not the loss for every investor or every stock. Different indexes, currencies, and measurement dates can produce different percentages.