The S&P 500 lost approximately 34% during the 2020 COVID-19 stock-market crash.
The decline ran from the index's February 19, 2020 record close to its March 23 low. Fears about the rapidly spreading COVID-19 virus, business shutdowns, travel restrictions, unemployment, and an oil-price shock caused investors to reassess economic prospects at exceptional speed.
The fall was unusually abrupt. U.S. exchanges triggered several circuit breakers in March as prices moved sharply downward. Central banks and governments then introduced large monetary and fiscal responses, while optimism about vaccines and economic reopening helped markets recover from the March low.
The approximate 34% figure describes the S&P 500's peak-to-trough decline, not its loss for the entire calendar year. The index finished 2020 higher than it began. Another common mix-up is treating the crash as one single trading session; it unfolded over several weeks, with the low on March 23.