The S&P 500’s largest one-day percentage fall during the 2020 COVID-19 crash was about 12% on March 16, 2020.
The index fell 12.0% as investors reacted to the accelerating pandemic, travel restrictions, business shutdowns, and extraordinary uncertainty about economic activity. The session also followed emergency monetary and fiscal announcements that failed to calm markets immediately.
Trading was halted temporarily under market-wide circuit breakers after the decline crossed the first threshold. The Dow Jones Industrial Average fell about 12.9% that same day, while the Nasdaq Composite lost roughly 12.3%.
The crash was unusually rapid. U.S. equities reached a bear-market low in March, then recovered strongly after unprecedented support from central banks and governments and optimism about vaccines and reopening.