The Dow Jones Industrial Average suffered its biggest one-day percentage loss on October 19, 1987, during the 1987 stock-market crash.
The Dow fell 508 points, or 22.6%, in a single session. That percentage decline remains the largest one-day percentage drop in the index’s history. Markets in other countries also plunged, making the episode a genuinely global crash rather than an isolated Wall Street event.
Several explanations have been proposed, including computer-driven portfolio insurance, overvalued shares, international trade tensions, and investor panic. No single cause fully explains the speed and scale of the selling.
The date is often called Black Monday. It should not be confused with Black Monday in 1929, a separate day during the Wall Street Crash when the Dow also suffered a major fall.