Which index recorded the biggest one-day percentage loss in the 1929 Wall Street Crash?

The Dow Jones Industrial Average recorded the biggest widely cited one-day percentage loss in the 1929 Wall Street Crash. On October 28, 1929, the Dow fell 12.8%, and it dropped another 11.7% on October 29.

The collapse followed a speculative boom in U.S. shares. Investors increasingly bought stocks on margin, meaning borrowed money magnified both potential profits and losses. When prices began to fall, margin calls forced more selling.

The Dow did not immediately reach its ultimate low after the October panic. It continued declining over the following years and reached a low of 41.22 on July 8, 1932, about 89% below its September 1929 peak.

The S&P 500 did not yet exist in its modern form; Standard & Poor’s introduced the Composite Index in 1923 and the 500-stock index in 1957. That makes the Dow the canonical index for this historical crash.