During the decade of the 1930s in which the Dow rose or fell by more than 20%. The month with the biggest Dow move was April 1933, when the Dow rose by 40.2%. In August 1932, furthermore, the Dow rose by 34.8%.
The biggest monthly losses during that decade were almost as big. The largest came in September 1931, when the Dow lost 30.7%.
These monthly changes dwarf what has been seen in the current bear market. The biggest calendar month loss so far came last October, when the Dow fell by 14.1%. The second biggest came in February, when the Dow fell 11.7%.
So the % moves back than far exceed anything we have yet seen.