Which date saw the largest one-day percentage fall in Dow Jones history during the 1987 crash?

The largest one-day percentage fall in Dow Jones history during the 1987 crash occurred on October 19, 1987.

That day became known as Black Monday. The Dow Jones Industrial Average fell 508 points, or 22.6 percent, in a single session. The percentage decline remains the index’s largest one-day loss, even though later crashes produced larger point declines because the index had grown substantially.

Several forces contributed to the sell-off, including investor anxiety about overvalued shares, rising interest rates, trade tensions, and portfolio-insurance strategies that automatically sold futures as markets fell. Selling spread rapidly between markets through increasingly connected financial systems.

The 1987 crash was severe but did not produce a depression comparable to the 1930s. The Dow recovered much of its loss relatively quickly, and regulators later introduced circuit breakers and other mechanisms intended to slow disorderly trading.