Which U.S. stock-market index fell 22.6% on October 19, 1987?

The U.S. stock-market index that fell 22.6% on October 19, 1987, was the Dow Jones Industrial Average.

October 19, 1987, became known as Black Monday. The Dow Jones Industrial Average lost 508 points, equivalent to 22.6% of its value, in the largest one-day percentage decline in its history. Markets in Hong Kong, Europe, Australia, and other regions also suffered major falls, making the event global rather than exclusively American.

Several factors contributed, including high valuations, rising interest rates, trade concerns, portfolio insurance, and computer-driven program trading. Researchers continue to debate the precise balance among these causes, but the speed and scale of selling exposed weaknesses in market infrastructure.

Unlike the 1929 crash, the 1987 collapse did not lead to a decade-long depression. Central banks supplied reassurance and liquidity, and the U.S. economy continued growing. The event nevertheless changed exchange rules and encouraged the development of trading halts designed to slow panic during extreme moves.