The Dow Jones Industrial Average lost 22.6% on 19 October 1987, the central day of the Black Monday crash.
The fall was extraordinary because it occurred during one trading session and exceeded every previous one-day percentage decline in the Dow. The index dropped 508 points, a large numerical move for the era, although percentage comparisons are more meaningful across different periods.
The collapse spread through financial centres in Europe, Asia, and the Pacific. Trading systems and order-processing procedures came under severe pressure as investors attempted to sell simultaneously. Program trading and portfolio-insurance strategies were among the explanations investigated afterward.
The 22.6% figure is often confused with the 1929 crash’s famous percentage losses or with the much smaller point decline on other dates. It refers specifically to the Dow’s one-day percentage change on 19 October 1987.