The largest single-day percentage fall ever recorded by the Dow Jones Industrial Average was 22.6%, on 19 October 1987.
That day became known as Black Monday. The Dow fell 508 points, but the percentage figure is the more meaningful comparison because the index level changes over time. A point decline that looks larger in a later era may represent a smaller percentage of the index.
The selling was part of a global market crisis. Investors faced concerns about valuations, interest rates, international trade, and currency policy. Computerized trading and portfolio-insurance programs also generated automatic sell orders as prices declined, increasing the speed and scale of the fall.
The record is often confused with modern point-loss records. For example, later crashes produced much larger numerical point drops because the Dow had risen to a far higher level. None of those later point records exceeded Black Monday's 22.6% percentage decline.