First Day Of Summer 2025 Australia 2025. This year the summer solstice is the 21st of december 2025. The summer solstice falls on december 21, 2025, and is the longest day of the year.

The summer solstice is the first day of astronomical summer, although the more logical metrological summer begins december 1st / june 1st (depending on hemisphere). This year’s summer solstice falls on june 20, 2025.