The Dow Jones Industrial Average suffered its largest one-day percentage loss on October 19, 1987, during the Black Monday crash.
The Dow fell 508 points, or 22.6%, in a single trading session. The percentage decline remains the largest one-day fall in the index’s history, although later crashes produced larger point losses because the index had grown much higher.
Black Monday was part of a global market collapse. Stock markets in Hong Kong, Europe, Australia, and Canada also fell sharply, and the selling continued across time zones. Program trading, portfolio insurance, overvalued shares, rising interest rates, and international financial tensions all contributed to the panic.
The crash did not produce a depression comparable to the 1930s. The U.S. Federal Reserve supplied liquidity, and the market eventually recovered. Black Monday is often confused with Black Tuesday in 1929, but the two events occurred nearly 58 years apart.