Which U.S. index fell 12.8% on 28 October 1929, during the Wall Street crash?

The Dow Jones Industrial Average fell 12.8% on 28 October 1929, during the Wall Street crash.

The day became known as Black Monday of 1929. The Dow lost 38.33 points, a fall of approximately 12.8 percent, as heavy selling overwhelmed the New York Stock Exchange. The following day brought another major decline, commonly called Black Tuesday.

The crash followed years of rising share prices, widespread margin buying, and growing concern about the strength of the economy. It did not single-handedly cause the Great Depression, but it damaged confidence and helped intensify a broader economic downturn.

The Dow is a price-weighted index of major U.S. companies, not a complete measure of every American stock. The S&P 500 did not yet exist in its modern form in 1929, so attributing this historical percentage to that index is anachronistic.