The largest one-day percentage fall in the Dow during the 1929 crash occurred on Black Monday, when it dropped 12.8%.
Black Monday was October 28, 1929, when the Dow Jones Industrial Average fell 38.33 points, or 12.82%. The next day, Black Tuesday, brought another enormous decline of about 11.7%, but Black Monday was the sharper percentage fall.
These consecutive losses followed weeks of nervous trading and attempts by major bankers to stabilize prices. The earlier Black Thursday, October 24, had also produced heavy selling, although a temporary support effort limited the closing decline.
The 1929 crash is often remembered mainly through Black Tuesday, which is why the Black Monday figure can be overlooked. The market’s later fall continued for years, and the Dow did not regain its September 1929 peak until 1954.