The Dow Jones Industrial Average fell approximately 12.8% on Black Tuesday, October 29, 1929.
That percentage represented an enormous loss for the era, especially because the Dow had already suffered sharp declines during the preceding week. Panic selling overwhelmed buyers, and the exchange recorded about 16 million shares traded, far above earlier daily volumes.
The percentage is calculated from the Dow’s closing level on October 28 to its close on October 29. Intraday prices moved differently, so figures describing the day can vary slightly depending on whether they refer to the close, the opening, or the low.
Black Tuesday was part of a longer collapse rather than an isolated event. The Dow eventually lost nearly 89% from its September 1929 peak to its July 1932 low, showing why the crash became linked with the wider Great Depression.