The largest single-day percentage drop in the Dow Jones Industrial Average before Black Monday occurred on October 28, 1929, when it fell 12.8 percent.
The day became known as Black Monday of 1929. The Dow lost 38.33 points, closing at 260.64, as selling intensified after the market had already weakened during the previous week. The following day, Black Tuesday, brought another enormous decline of about 12 percent.
This 1929 percentage record was surpassed on October 19, 1987, when the Dow fell 22.6 percent. That distinction is important because the points lost in a market are not directly comparable across eras: a 500-point move means something very different at different index levels.
The 1929 crash continued after these two famous sessions. The Dow eventually reached its low in July 1932, nearly 89 percent below its September 1929 peak. The crash became a lasting symbol of speculative excess and financial panic.