The last day of summer in the UK depends on whether one refers to the meteorological or astronomical definition of summer:
- Meteorological summer in the UK always ends on August 31. This is because the meteorological seasons are divided into full months: summer includes June, July, and August.
- Astronomical summer ends at the autumnal equinox, which in 2025 will be on September 22 at 19:19 BST. This marks the point when the sun crosses the celestial equator going south, signaling the start of autumn.
Thus, the last day of summer in the UK is August 31 according to meteorological seasons, and September 22 according to astronomical seasons.
