What was the largest one-day percentage loss in the Dow Jones Industrial Average before 1987?

Black Monday, 1929, was the largest one-day percentage loss in the Dow Jones Industrial Average before 1987.

On October 28, 1929, the Dow fell 12.82%. The plunge followed the major sell-off on Black Thursday, October 24, and came one day before the even more famous Black Tuesday decline in the number of points traded and shares sold. Panic selling and margin calls forced investors to liquidate positions rapidly.

The 1929 crash is often discussed as one continuous event rather than a single session, but the dates had different market movements. Black Monday in 1987 later produced a larger percentage drop, while Black Tuesday in 1929 remains strongly associated with the crash’s public memory. Percentage loss and point loss are different measures, so rankings can change depending on which measure is used.