The Dow Jones Industrial Average lost 22.6% on October 19, 1987, the first day of the 1987 stock-market crash in New York.
The decline was extraordinary because it occurred in a single trading session. The Dow dropped 508 points, while other major markets also suffered steep losses. Concerns about overvalued shares, trade tensions, interest rates, and automated selling contributed to the panic.
The percentage is more meaningful than the point total because the Dow’s level has changed dramatically over time. A 508-point move would represent a much smaller percentage today than it did in 1987.
Black Monday led to major changes in market supervision. Trading halts and circuit breakers were developed to give investors time to absorb information during exceptionally rapid declines.