The S&P 500 reached its closing low during the COVID-19 stock-market crash on March 23, 2020.
The index closed at 2,237.40 that day, after weeks of rapid selling caused by the spread of COVID-19 and the economic shock of measures used to slow it. The collapse included several sessions in which US market-wide circuit breakers were triggered, including March 9, March 12, March 16, and March 18.
The March 23 close marked the low for the initial bear market. Markets then rallied as governments and central banks announced large fiscal, monetary, and emergency-lending responses. The S&P 500 eventually recovered its pre-crash closing high in August 2020, although economic conditions remained unusually uncertain.
The date can be confused with March 16, which produced a larger one-day percentage drop of 12.0 percent for the S&P 500. March 23 was the trough of the decline, not the day of its steepest single-session fall.