October 19, 1987, marked the largest one-day percentage fall in the Dow Jones Industrial Average during the 1987 stock-market crash.
The day became known as Black Monday. The Dow Jones Industrial Average fell 508 points, or 22.6 percent, in a single trading session. That percentage decline remains the index's largest one-day loss, although later crashes produced larger point losses because the index was much higher.
The decline was international rather than confined to the United States. Stock markets in Hong Kong, Australia, the United Kingdom, and other financial centers also suffered severe falls. Investors were worried about high valuations, rising interest rates, trade tensions, and the growing use of automated portfolio-insurance strategies.
Black Monday is sometimes confused with the 1929 crash, but the two events occurred in different economic eras. The 1987 crash did not lead to a decade-long depression, and the Dow recovered much of its loss relatively quickly. Regulators later introduced circuit breakers to slow extreme market declines.