The fastest one-day percentage fall in the S&P 500 during the March 2020 COVID-19 crash was about 12%.
On March 16, 2020, the S&P 500 fell 11.98%, commonly rounded to 12%. The decline came as investors reacted to the rapid spread of COVID-19, restrictions on travel and economic activity, and extraordinary uncertainty about corporate earnings and global growth.
The March 2020 crash followed a long bull market but unfolded unusually quickly. U.S. exchanges triggered circuit breakers several times as prices moved sharply. The Federal Reserve cut interest rates to near zero and introduced emergency programs, while governments announced fiscal support. The 12% figure is the S&P 500’s percentage change for that trading day; it is not the index’s total decline from its February peak to its March low, which was about 34%.