The 19 October 1987 day when stock markets around the world suffered their largest one-day percentage falls was called Black Monday.
The Dow Jones Industrial Average fell 508 points, or 22.6%, in a single session. That percentage decline remains the largest one-day percentage drop in the Dow’s history. Markets in Hong Kong, Australia, the United Kingdom, and elsewhere also recorded severe losses.
Several explanations have been studied, including rising interest rates, worries about trade and the U.S. dollar, program trading, and portfolio-insurance strategies. Automated selling could reinforce falling prices, although no single cause fully explains the global event.
Black Monday is sometimes confused with the 1929 crash’s Black Monday, which occurred on 28 October 1929. The shared nickname refers to the dark market losses, but the two events happened 58 years apart and had different economic backgrounds.