The Dow Jones Industrial Average’s record one-day percentage loss on October 19, 1987, was 22.6%.
On that Monday, the Dow fell 508 points, or 22.6%, in a single trading session. The decline was the largest one-day percentage drop in the index’s history and occurred in the United States after sharp falls had already struck markets in Asia and Europe.
Several forces contributed, including concerns about economic growth, international trade imbalances, rising interest rates, and computerized portfolio-insurance trading. Program trading could automatically sell futures or shares as prices fell, adding pressure during an already panicked market.
The crash did not produce a depression like the 1929 collapse. Markets stabilized after coordinated action by central banks and other authorities. The episode also encouraged reforms, including circuit breakers designed to pause trading during exceptionally rapid declines.