What was the largest one-day percentage drop in the Dow Jones Industrial Average?

The largest one-day percentage drop in the Dow Jones Industrial Average was Black Monday in 1987. On October 19, 1987, the Dow lost 22.6 percent of its value during one trading session.

The percentage measure matters because later crashes produced larger losses in points as the index grew. Black Monday remains the record when the decline is measured as a share of the Dow’s closing level. The fall spread across global markets rather than remaining a purely American event.

Several forces were associated with the sell-off, including concerns about interest rates and trade deficits, valuation worries, and computerized portfolio-insurance strategies that encouraged selling as prices fell. Black Monday is therefore different from the 1929 crash, whose decline unfolded across several severe sessions and was followed by a much longer economic depression.