Which U.S. stock index lost about 23% during the 1987 Black Monday crash?

The Dow Jones Industrial Average lost about 23% during the 1987 Black Monday crash.

On October 19, 1987, the Dow dropped 508.00 points, closing at 1,738.74. Measured against its previous close, the fall was 22.61%, commonly rounded to 23%. The index tracks 30 prominent U.S. companies, so its decline became the most widely quoted measure of the day’s Wall Street damage.

The S&P 500 also suffered a severe decline, falling 20.47% on the same date. The Nasdaq Composite dropped as well, but the Dow’s record-setting percentage loss made it the symbolic centerpiece of reporting about Black Monday. The crash followed sharp declines in several overseas markets, including Hong Kong and the United Kingdom.

The event did not lead to a prolonged economic depression comparable to the 1930s. The Federal Reserve supplied liquidity, and the market eventually recovered. The episode nevertheless changed market regulation and encouraged the development of trading halts and coordinated responses.