What was the name of the 1987 stock-market crash’s biggest single-day event?

The biggest single-day event of the 1987 stock-market crash was called Black Monday.

Black Monday occurred on October 19, 1987, when the Dow Jones Industrial Average plunged 508 points, or 22.6 percent. That remains the largest one-day percentage decline in the Dow’s history, even though later crashes produced larger point losses.

The fall spread rapidly across international markets, including Hong Kong, London, and Australia. Explanations include program trading, portfolio insurance, overvalued shares, rising interest rates, and market structures that amplified selling.

Black Monday did not lead to a depression like the 1929 crash. Central banks supplied liquidity, and the United States economy continued expanding. The episode did, however, prompt major changes to market safeguards, including circuit breakers designed to pause trading during extreme declines.