The Dow Jones Industrial Average fell nearly 89% from its 1929 peak to its 1932 low during the Wall Street Crash.
The Dow reached a peak of 381.17 on September 3, 1929. After a series of sharp declines, it reached a low of 41.22 on July 8, 1932. That fall represented one of the most severe collapses in the history of a major U.S. stock index.
The crash did not cause the entire Great Depression by itself. Excessive speculation, purchases made with borrowed money, weak banking conditions, reduced industrial production, and falling consumer demand all contributed to the wider economic crisis. The banking failures and deflation that followed made the downturn much deeper and longer.
The Dow eventually recovered its pre-crash closing high in November 1954, more than 25 years after the 1929 peak. The 89% figure describes the peak-to-trough index decline, not a one-day loss and not the fall in every individual share.