The largest one-day percentage fall in the Dow Jones Industrial Average was 22.6%, recorded during the 1987 crash.
The decline occurred on October 19, 1987, a day now called Black Monday. The Dow lost 508 points, and the percentage drop was far larger than the one-day declines seen during the 1929 Wall Street Crash.
The sell-off was international. Stock markets in Asia and Europe had already fallen, and the panic reached the United States. Investors were responding to economic concerns, high market valuations, interest-rate conditions, and automated trading practices that could accelerate falling prices.
The statistic refers specifically to the Dow’s percentage change from the previous close. It should not be confused with the largest point decline, because point losses depend on the index’s level at the time.