When Is The 1st Day Of Summer 2025. For example, it can help you find out how long until summer 2025? In 2025, the summer solstice will occur on june 21, at 02:42 gmt in the northern hemisphere, and on december 21, at 15:03 gmt in the southern hemisphere.

June 21st, 2025 is the official start date of the summer. June, july, august and september.