The Dow Jones Industrial Average suffered its largest percentage loss of the 1929 Wall Street Crash on October 28, 1929.
The Dow fell 12.82% that day, then dropped another 11.73% on October 29, later known as Black Tuesday. These declines followed weeks of nervous trading after the market had reached a record high in September.
October 24, known as Black Thursday, brought heavy selling and an emergency effort by major bankers to support selected stocks. The temporary calm did not last. Selling intensified on October 28 and 29 as investors rushed to liquidate positions, often using borrowed money.
The crash did not alone cause the Great Depression, but it severely damaged confidence and exposed the risks of speculation and margin buying. The Dow ultimately lost almost 89% from its 1929 peak to its 1932 low.