During the 1987 Black Monday crash, the S&P 500 lost 20.47% on October 19.
The fall was the largest one-day percentage decline in the index’s history. The Dow Jones Industrial Average also suffered its largest one-day percentage drop, falling 22.6%, while markets in several other countries recorded exceptionally severe losses.
Several factors contributed to the crash, including overvalued share prices, rising interest rates, trade concerns, and computerized trading strategies. Portfolio insurance programs amplified selling as prices fell, although no single cause explains the entire event.
Black Monday is sometimes confused with the 1929 Wall Street crash or with the broader 1987 market crash. October 19 was the most dramatic day, but the worldwide decline unfolded across multiple trading sessions.