First day of summer 2025 kicks off with the summer solstice, bringing heat and sunshine ahead

When is the first day of summer 2025: Get ready for summer! The summer solstice on June 20, 2025, marks the official start of astronomical summer, bringing the longest day of the year with over 15 hours of sunshine in many cities. Expect rising temperatures into the 90s after the solstice, as the sun reaches its northernmost point, providing the most direct sunlight.