The Dow Jones Industrial Average’s largest single-day percentage fall during the 1929 Wall Street Crash was about 12.8%, recorded on Black Monday, October 28.
The following day, Black Tuesday, brought another fall of roughly 12%, making the two sessions among the most dramatic consecutive declines in the index’s history. Selling overwhelmed the New York Stock Exchange, and investors rushed to liquidate shares as confidence collapsed.
The crash followed a spectacular rise in stock prices during the 1920s, when widespread optimism and buying on margin helped push valuations higher. When prices turned down, margin calls forced investors to sell, adding pressure to the decline.
The 1929 crash is closely associated with the Great Depression, but historians treat the economic collapse as a broader process involving banking failures, deflation, declining production, and international financial problems. The crash was a major catalyst rather than a complete explanation.