Which U.S. stock index fell 22.6% during the 1987 crash’s largest single-day percentage decline?

The Dow Jones Industrial Average fell 22.6 percent during the 1987 crash’s largest single-day percentage decline. The drop occurred on October 19, 1987, a day widely known as Black Monday.

The decline was driven by several interacting concerns, including high valuations, rising interest rates, trade and currency tensions, and program trading. Computerized portfolio strategies and stop-loss orders may have accelerated selling, although historians and market specialists continue to debate the relative weight of each factor.

Unlike a normal point movement, a percentage fall measures the loss relative to the index’s starting level. The Dow’s 22.6 percent decline remains the largest one-day percentage fall in its history. The S&P 500 also dropped heavily that day, but the question’s canonical index is the Dow.

The Federal Reserve and other central banks responded with liquidity support and reassurance. Markets eventually stabilized, and the crash did not lead to a Great Depression-style contraction, though it permanently changed market regulation and trading practices.