The Dow Jones Industrial Average lost about 89% during the entire 1929 crash, measured from its September 1929 peak to its July 1932 low. This makes the episode one of the deepest prolonged declines in major U.S. stock-market history.
The Dow reached a pre-crash peak of about 381.17 on September 3, 1929. After the October panic, it continued falling through bank failures, deflation, unemployment, and the wider contraction that became the Great Depression. By July 8, 1932, it had fallen to about 41.22.
The figure is often confused with the percentage loss on a single day. The Dow dropped about 12.8% on Black Monday in 1987 and about 12% on Black Tuesday in 1929, but neither single session represents the full 1929 decline. The Dow did not regain its 1929 peak until 1954.