During the 1987 Wall Street Crash, the Dow Jones Industrial Average lost 22.6% on Black Monday.
The decline occurred on October 19, 1987, when the Dow fell 508 points, the largest one-day percentage drop in its history. Selling spread rapidly from Hong Kong and Europe to the United States.
Several factors were blamed, including high valuations, trade and interest-rate worries, and computerized portfolio-insurance trading. The exact combination remains debated, but the scale of automated selling amplified the decline.
The 22.6% figure applies to the Dow’s one-day percentage loss, not to every market. Australia’s market suffered an even larger fall during the wider international crash, while U.S. markets later adopted circuit breakers.