Which index lost about 22.6% on Black Monday, the worldwide stock-market crash of October 19, 1987?

The Dow Jones Industrial Average lost about 22.6% on Black Monday, the worldwide stock-market crash of October 19, 1987.

The one-day percentage fall was the largest in the Dow’s history. It followed substantial declines in other markets, including Hong Kong, London, and Australia, and spread rapidly through increasingly interconnected financial systems. The crash was not a repeat of 1929: the banking system did not collapse and the United States did not enter a depression.

Researchers have linked the fall to several interacting factors, including high valuations, fears about interest rates and trade deficits, portfolio insurance, and computerized trading strategies. No single universally accepted cause explains every market’s movement. The Federal Reserve, led by Alan Greenspan, issued a statement affirming its readiness to provide liquidity.

The Dow’s percentage loss is often confused with its points loss. The index dropped 508 points that day, but the historically important statistic is the 22.6% decline. Markets eventually recovered, and regulatory changes followed.