First Day Of Summer 2025 Date And Time. This is the longest day of the year and marks the start of summer in the northern hemisphere. Find out the date when summer is in 2025 and count down the days until summer with a countdown timer.

For those of us in the northern hemisphere, the earth tilts mostly toward the sun during this time. 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.