Which US stock index fell most sharply during the 1987 Black Monday crash?

The Dow Jones Industrial Average fell most sharply in the headline US market measure during the 1987 Black Monday crash.

On 19 October 1987, the Dow lost 508 points, equivalent to 22.6% of its value. The fall was extraordinary even by the standards of earlier market panics and remains the index's largest one-day percentage decline. Other major US indexes also suffered substantial losses, but the Dow's record made it the best-known measure of the event.

The Dow is a price-weighted index of 30 large US companies, so its point movements do not directly equal the performance of the entire US stock market. The S&P 500, which is capitalization-weighted and broader, is often preferred for measuring overall large-company market performance.

Black Monday affected financial centers around the world and prompted changes to market infrastructure. US exchanges later adopted circuit breakers that can temporarily halt trading after extreme index declines, helping reduce disorderly selling during future shocks.