Which U.S. stock index lost the most during the 1987 Black Monday crash?

The U.S. stock index that lost the most during the 1987 Black Monday crash was the Dow Jones Industrial Average.

The Dow dropped 508 points on October 19, 1987, corresponding to a 22.6 percent fall. Because the Dow contained only 30 large companies, it was not a complete measure of the U.S. market, but its dramatic decline became the event’s most widely quoted statistic.

The S&P 500 also fell sharply, declining about 20 percent that day, while the Nasdaq Composite dropped by a similar order of magnitude. The Dow’s percentage loss remains a famous benchmark for comparing later market shocks.

The crash exposed risks in automated selling programs and prompted the creation of coordinated market-wide trading halts. Those safeguards are designed to pause trading when prices move unusually fast, giving investors time to absorb information rather than react mechanically.