Black Monday caused the Dow Jones Industrial Average’s largest one-day percentage loss, falling 22.6% on October 19, 1987.
The decline followed severe selling across global markets. Hong Kong’s market fell first on October 19 local time, and the panic spread through Europe before reaching New York. The Dow lost 508 points, a record point decline at the time.
Several factors contributed, including high share valuations, rising interest rates, trade tensions, and computerized portfolio-insurance trading. Portfolio insurance used automatic selling rules that could intensify a falling market, although historians do not identify one single cause.
Black Monday is often confused with the October 1929 Wall Street Crash. The 1987 event was a separate crash, and despite its dramatic one-day fall, the U.S. economy did not enter a depression afterward. Markets later recovered, while regulators introduced safeguards such as trading halts.