The FTSE 100 suffered a 12.22% one-day percentage fall during the 1987 global stock-market crash.
The decline occurred on October 19, 1987, the day known internationally as Black Monday. The United Kingdom was one of several major markets hit by the worldwide wave of selling that began in Asia and moved through Europe and North America. The FTSE 100 fell sharply as investors reassessed valuations and financial risks.
Black Monday’s international character distinguishes it from a crash confined to one exchange. Markets in Hong Kong, Australia, Britain, the United States, and other countries recorded major losses. In the United States, the Dow’s percentage fall was even larger at 22.6%.
The FTSE 100 figure is sometimes confused with the Dow’s 22.6% decline because both happened on the same global crash day. They measure different indexes in different markets, so the percentages should not be treated as interchangeable.