October 19, 1987, the worst day of the 1987 stock-market crash, was called Black Monday.
The Dow Jones Industrial Average fell 508 points, or 22.6%, on that Monday. The percentage decline remains the largest single-day drop in the Dow's history. Shares also plunged in other major markets, including Hong Kong, London, and Australia, making the event an international crash rather than only a U.S. market disturbance.
Several factors contributed. U.S. stocks had risen sharply before the crash, and investors were worried about interest rates, trade deficits, and an overvalued market. Computerized portfolio-insurance strategies automatically sold futures as prices dropped, adding to the downward pressure. The exact balance of causes remains debated.
Black Monday is sometimes confused with Black Tuesday, the October 29, 1929, sell-off. The two names describe different crashes, separated by nearly six decades.