The largest one-day percentage gain in the Dow Jones Industrial Average was 15.34%, recorded on March 15, 1933.
The gain occurred during a powerful rebound after the long bear market that followed the 1929 Wall Street Crash. The Dow rose 8.26 points, from 53.84 to 62.10, producing the index's largest percentage increase in its history.
March 1933 was also a moment of intense banking stress in the United States. President Franklin D. Roosevelt declared a national bank holiday shortly after taking office, and the Emergency Banking Act supported the reopening of solvent banks. Improving confidence contributed to the market surge.
A percentage gain is different from a point gain: the Dow's index level was much lower in 1933 than in later decades. Consequently, a modest point movement could represent a very large percentage change.