Which U.S. stock index lost nearly 23% during the one-day 1987 Black Monday crash?

The Dow Jones Industrial Average lost nearly 23% during the one-day 1987 Black Monday crash.

On October 19, 1987, the Dow fell 508 points, equal to 22.6% of its value. It was the largest one-day percentage decline in the index’s history and remains a benchmark for the severity of that global market shock. Markets in other countries also dropped sharply as selling spread across time zones.

The crash had several contributing factors. Program trading and portfolio-insurance strategies accelerated selling, while investors were also concerned about overvalued shares, trade tensions, and monetary conditions. Investigations did not identify one universally accepted single cause.

The percentage figure is more meaningful than the point total when comparing eras. A 508-point move was enormous in 1987, but modern index levels make raw point comparisons misleading. The S&P 500 and other indexes also fell heavily that day, yet the Dow’s 22.6% loss is the fact most often cited for the U.S. session.