Fall Equinox 2025 Day 1. In 2025, the last day of summer in the northern hemisphere is september 22! The first day of fall in 2025 is sunday, sept.

September 22 is the autumnal equinox for 2025, marking the earliest start to the fall season for the northern hemisphere since 1796. This sunday, the autumnal equinox is upon us, and with it, a shift to shorter days, longer nights and the astronomical start of fall in the northern hemisphere.