The 1987 market crash preceded by the biggest one-day percentage fall in the FTSE 100 was Black Monday.
On October 19, 1987, the FTSE 100 fell 26.45%, its largest one-day percentage decline. The same global episode saw the Dow Jones Industrial Average fall 22.6%, while markets in Hong Kong, Australia, and other financial centers also suffered major losses. The synchronized movement showed how international markets had become increasingly connected.
Several explanations were examined, including high valuations after a long rise, rising interest rates, currency and trade concerns, and automated selling strategies. Portfolio insurance programs could generate additional sell orders as prices dropped. The crash also exposed differences in trading rules and settlement systems across countries.
The date is called Black Monday in Britain and internationally, although other financial collapses have used the same label. The FTSE 100 was created in 1984, so this statistic belongs to that index’s history rather than to the older 1929 crash.