The Dow Jones Industrial Average lost approximately 22.6% on Black Monday, 19 October 1987.
That percentage remains the Dow’s largest one-day decline, even though later crashes produced larger point losses because the index level had grown over time. The distinction between points and percentages is important: a 1,000-point fall means something different when an index stands at 5,000 than when it stands at 30,000.
Black Monday was part of a global sell-off. Investors were worried about valuation, interest rates, currency tensions, and the U.S. trade deficit. Automated and formula-based trading systems also sold as prices weakened, intensifying the speed of the decline. The precise weighting of each cause remains debated by financial historians.
Markets recovered some ground soon afterward, helped by central-bank reassurance and emergency liquidity measures. Regulators also developed coordinated trading halts, now known as circuit breakers, to pause trading during exceptionally rapid declines. The 22.6% figure applies specifically to the Dow’s one-day percentage move, not to the total decline from its peak to its later low.