The Dow Jones Industrial Average lost 12.8% on October 28, 1929, one of the defining sessions of the Wall Street Crash.
The day became known as Black Monday, followed by another severe decline on Black Tuesday, October 29. The market had already fallen from its September peak, but selling accelerated as investors rushed to exit positions and brokers struggled with enormous volumes of orders.
The crash was part of a wider economic breakdown rather than the sole cause of the Great Depression. Banking failures, falling demand, debt burdens, protectionist policies, and monetary conditions all contributed to the prolonged downturn. The Dow continued falling after October 1929 and reached its major low in 1932.
This 12.8% figure is different from the 11.7% loss on October 29 and the 22.6% fall recorded on Black Monday in 1987. The similar names can make the two historical crashes easy to confuse.