Black Monday, October 28, 1929, marked the biggest one-day percentage fall in the Dow Jones Industrial Average during the 1929 Wall Street Crash.
The Dow fell 12.82% that day, after already dropping sharply on the preceding Black Thursday. Heavy selling overwhelmed the New York Stock Exchange, and the decline continued into Black Tuesday, October 29, when the Dow lost another 11.73%.
The crash followed years of rapidly rising share prices, widespread speculation, and buying stocks with borrowed money. Investors increasingly feared that prices had moved far beyond the underlying economy. The crash did not single-handedly cause the Great Depression, but it intensified financial distress and damaged confidence.
A common mix-up is to call Black Tuesday the largest percentage fall. Black Tuesday was more famous because of its enormous trading volume and the collapse of confidence, but Black Monday produced the larger percentage loss. The Dow did not regain its 1929 peak until 1954.