The 1929 trading day when the Dow Jones Industrial Average fell nearly 13% was Black Monday.
Black Monday occurred on October 28, 1929, during the Wall Street Crash. The Dow dropped 38.33 points, or 12.82%, as heavy selling overwhelmed the New York Stock Exchange. The next day, October 29, brought another severe decline and became known as Black Tuesday.
The crash followed years of rising share prices, widespread speculation, and purchases made with borrowed money. When prices began falling, margin calls forced investors to sell, creating additional downward pressure. The collapse damaged confidence and contributed to the economic conditions surrounding the Great Depression.
Black Thursday, October 24, was the first dramatic sell-off commonly associated with the crash, but it was not the largest percentage decline among the famous 1929 sessions. Black Monday and Black Tuesday are also distinct from the 1987 event, which reused the name Black Monday for a much larger one-day percentage fall.