Fall, also known as autumn, typically starts on the autumnal equinox, which in 2025 occurs on Monday, September 22. This marks the official astronomical beginning of fall in the Northern Hemisphere. Meteorologically, however, fall is often considered to start on September 1 and lasts through November 30. The autumnal equinox is the precise moment when day and night are approximately equal in length, symbolizing the transition from summer to fall.