The Dow Jones Industrial Average lost 12.8% on 28 October 1929, the trading day known as Black Monday.
The fall came after a period of intense speculation in U.S. shares during the 1920s. Investors frequently bought stock with borrowed money, and prices rose far faster than many companies’ underlying earnings. By late October, confidence had weakened and selling accelerated.
Black Monday was followed by Black Tuesday on 29 October, when the Dow fell another 12%. Together, the two sessions represented a dramatic collapse in market confidence. The crash continued through subsequent months, and the Dow eventually lost almost 89% from its September 1929 peak to its July 1932 low.
The crash is closely associated with the Great Depression, but historians do not treat it as the sole cause. Bank failures, falling demand, debt, deflation, international financial problems, and policy decisions all contributed to the economic catastrophe. The crash itself occurred before the deepest years of the depression.