Which U.S. stock exchange saw its largest one-day percentage fall on October 19, 1987?

The New York Stock Exchange saw its largest one-day percentage fall on October 19, 1987, when the Dow Jones Industrial Average plunged 22.6%.

The date became known as Black Monday. Selling spread across international markets after earlier declines in Asia and Europe. Portfolio insurance, computerized trading, high valuations, trade tensions, and concerns about interest rates were among the factors studied as possible contributors.

The collapse was severe but did not develop into a depression like the crash of 1929. The U.S. economy continued expanding, although the market shock damaged confidence and exposed weaknesses in trading systems. The Dow recovered over time.

The crash led to major reforms, including coordinated trading halts known as circuit breakers. These mechanisms are designed to pause trading when prices move too rapidly. Black Monday is sometimes confused with the 1929 market episodes, which used the same weekday labels but occurred in a very different economic and institutional setting.