The largest one-day percentage drop in the Dow Jones Industrial Average was 22.6%, recorded on October 19, 1987.
The day became known as Black Monday. The Dow lost 508 points, and selling spread quickly through financial markets in Europe, Asia, and North America. Because percentage comparisons account for the index’s level, the 22.6 percent figure remains more historically meaningful than the raw 508-point loss.
The crash followed a period of strong gains and growing concerns about interest rates, trade deficits, currency values, and market valuations. Computerized trading strategies amplified the downward movement by automatically selling as prices fell.
Later crashes produced larger point losses because the Dow had reached much higher levels. For example, March 16, 2020, produced a larger point decline, but not a larger percentage decline. This distinction explains why Black Monday retains the record.