The Dow Jones Industrial Average fell nearly 89% from its September 1929 peak to its July 1932 low.
The Dow reached a closing high of 381.17 on September 3, 1929. After the Wall Street Crash and the worsening economic conditions of the Great Depression, it eventually fell to 41.22 on July 8, 1932. That decline was approximately 89% from peak to trough.
The loss was much larger than the one-day declines associated with Black Monday and Black Tuesday. It unfolded over almost three years, as bank failures, deflation, reduced industrial production, and falling business investment reinforced one another.
The Dow did not recover its 1929 closing high until November 23, 1954. This long recovery period is why the 1929–1932 episode is often discussed as a prolonged market collapse rather than only a single day of panic.