Which U.S. stock index lost 22.6% on Black Monday in 1987, its largest one-day percentage fall?

The Dow Jones Industrial Average lost 22.6% on Black Monday in 1987, its largest one-day percentage fall.

On October 19, 1987, the Dow dropped 508 points, which represented 22.6% of its closing value from the previous trading day. Because the index was calculated from 30 major U.S. companies, the percentage loss reflected a broad collapse in leading industrial and financial shares rather than a single-company failure.

The decline was part of a worldwide market shock. Major exchanges in Hong Kong, London, and other financial centers also suffered steep falls. Investors were worried about valuations, interest rates, currency tensions, and the U.S. trade deficit.

The 22.6% figure is a percentage loss, not the Dow's largest point loss. Point records depend on the index's level and therefore changed substantially as the Dow rose over later decades. The S&P 500 and Nasdaq also fell sharply that day, but neither is the index identified by this specific record.