Which index suffered the world’s largest one-day percentage fall on 19 October 1987?

The Dow Jones Industrial Average suffered the world’s largest one-day percentage fall on 19 October 1987.

That date became known as Black Monday. The Dow dropped 508 points, or 22.61%, in one trading session. The percentage decline remains the largest single-day fall in the index’s history, even though later crashes produced larger point losses because the index level was much higher.

Several factors contributed to the panic, including high valuations, worries about interest rates and economic conditions, international market weakness, and computerized program trading. Selling pressure moved rapidly across global exchanges, making the event an international stock-market crash rather than an isolated New York episode.

The crash also prompted regulators and exchanges to reconsider market safeguards. Circuit breakers were introduced or expanded to pause trading during exceptionally sharp declines. Black Monday is often confused with the 1929 crash, but the two occurred 58 years apart and had different economic and technological contexts.