What Is The First Day Of Summer 2025 Calendar. No world body has designated an official day to start each new season, and different schools of thought or traditions define the seasons in. The first day of summer is also known as the summer solstice, and in 2025 it happens on thursday, june 20 at 4:51 p.m.

 — this year, the first day of summer, also known as the summer solstice, is thursday, june 20. Here are the equinox and solstice dates—plus, answers to common questions.