Autumn in 2025 starts on Monday, September 22, 2025. This date marks the beginning of astronomical autumn, which corresponds to the autumnal equinox when day and night are approximately equal in length. Meteorologically, autumn starts earlier on September 1 and lasts until November 30, but the astronomical definition is the more traditional one used to mark the seasonal change in Earth's position around the Sun in 2025. Autumn will then end on Sunday, December 21, 2025.