The Dow Jones Industrial Average lost 12.8% on the first Black Monday of 1929.
On October 28, 1929, the Dow fell 38.33 points, equivalent to 12.8% of its value. The decline followed growing concern that share prices had become unsustainably high and that investors were using excessive borrowed money.
Selling intensified the next day, October 29, which became known as Black Tuesday. The crash damaged confidence, but it was one part of a broader economic breakdown that developed into the Great Depression. Industrial production, employment, and international trade later suffered severe declines.
The 1929 crash is often described using several dramatic dates. Black Monday was October 28, Black Tuesday was October 29, and the market had already fallen substantially from its September peak before those sessions.