During the 1987 stock-market crash, which U.S. index suffered its largest one-day percentage drop?

During the 1987 stock-market crash, the Dow Jones Industrial Average suffered the largest one-day percentage drop among major U.S. indexes.

On Black Monday, October 19, 1987, the Dow fell 508 points, or 22.6 percent. That remains its largest one-day percentage decline, although later crashes produced larger point losses because the index had reached much higher numerical levels.

The sell-off was global. Markets in Hong Kong, Australia, the United Kingdom, and other countries also plunged. Analysts have linked the crash to high valuations, economic concerns, portfolio insurance, and automated trading strategies that intensified selling. No single cause fully explains the event.

The 1987 crash differed from 1929 in an important way: the economy did not enter a depression afterward. The Federal Reserve supplied liquidity, and markets eventually recovered. The crash also encouraged reforms, including circuit breakers designed to pause trading during extreme declines.