First Day Of Summer 2025 Date. Summer 2025 starts on friday, june 20th in the northern hemisphere, with the first day of summer being the longest daylight day of the year with the earth's axis having reached its furthest tilt and begins to change directiion back. What day is the first day of summer 2025 the first day of summer in 2025 isnt a single universally agreed upon date it depends on which definition of summer you.
In 2026, it will fall on sunday, june 20th. This day is also known as the summer solstice.