October 19, 1987, saw the largest one-day point loss in the Dow Jones Industrial Average during the 1987 crash.
The Dow lost 508 points that Monday, equivalent to 22.6% of its value. Although later years produced larger point declines because the index had grown much higher, the percentage fall remains the key historical comparison.
Trading was overwhelmed by sell orders linked to portfolio insurance, derivatives hedging and investor fear. Markets in Asia and Europe had already weakened, so selling fed across time zones and intensified when U.S. trading opened.
Unlike the 1929 crash, the 1987 episode did not lead to a decade-long depression. The Federal Reserve supplied liquidity, companies continued operating and markets eventually recovered. Regulators subsequently introduced circuit breakers and coordinated procedures for extreme volatility.