Last Day Of Summer 2025. The first real big one may have to wait. Thursday, june 20 is the official first day of northern astronomical summer for 2025 — summer solstice— which is the longest day of the year for this half of the.

As a meteorological season, the last day of summer is aug. Summer begins with the solstice on thursday, june 20, 2025, marking the astronomical first day of summer in the northern hemisphere.