Which U.S. stock-market index fell 12.8% on Black Monday, October 28, 1929?

The Dow Jones Industrial Average fell 12.8% on Black Monday, October 28, 1929.

The Dow was the best-known measure of major U.S. shares during the Wall Street Crash. After years of rising prices and widespread speculation, selling intensified in late October. The index lost nearly 13% on October 28 and another 11.7% on Black Tuesday, October 29.

The crash did not by itself create every condition of the Great Depression, but it damaged confidence, reduced wealth, and exposed weaknesses in banks and businesses. The Dow had reached a pre-crash peak of 381.17 in September 1929 and would not regain that level until 1954.

A common mix-up is treating the Dow as a broad measure of the entire U.S. market. It is a price-weighted index of 30 large companies, whereas the S&P 500 covers 500 major companies using a different methodology. Black Monday in 1929 also differs from Black Monday in 1987, which was a separate global market shock.