Which major U.S. stock index lost 22.6% on Black Monday in 1987?

The Dow Jones Industrial Average lost 22.6% on Black Monday, 19 October 1987.

The decline was the largest one-day percentage fall in the index’s history. The Dow dropped 508 points, closing at 1,738.74 after investors sold shares across many industries. The scale of the movement made Black Monday a defining event in modern financial history.

The S&P 500 and Nasdaq Composite also fell sharply, but the Dow’s 22.6% loss is the figure most often cited for the crash. The Dow is a price-weighted index of major U.S. companies, while the S&P 500 tracks a broader group of large-cap companies using a different weighting method.

The crash spread internationally, with major exchanges in Asia and Europe recording substantial losses. Investigations and later analysis pointed to valuation concerns, macroeconomic anxiety, and automated trading strategies as contributing factors. Trading halts and circuit breakers were subsequently developed to reduce panic during extreme declines.