Which stock-market crash produced the largest one-day percentage fall in the Dow Jones Industrial Average?

Black Monday in 1987 produced the largest one-day percentage fall in the Dow Jones Industrial Average.

On October 19, 1987, the Dow Jones Industrial Average dropped 508 points, or 22.6 percent, in a single trading session. The decline was the biggest one-day percentage loss in the index’s history, a record that remains notable even though the Dow’s point values are now much larger.

The crash spread rapidly through international markets. Hong Kong fell first, followed by other Asian, European, and North American markets. Explanations included overvalued shares, rising interest rates, trade tensions, and computerized portfolio-insurance selling that intensified the rush to exit.

Unlike the 1929 crash, 1987 did not lead to a decade-long depression. The U.S. Federal Reserve, led by Alan Greenspan, supplied liquidity and reassured financial institutions. Trading rules were later changed, including the introduction of circuit breakers designed to pause markets during exceptionally sharp falls.