When Does British Summer Time Start 2025. 16 rows view here when the clock must be set one hour forward or backward (summertime / daylight saving) for the next years including 2025. 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.
They spring forward an hour in march and go back an hour in. When does british summer time start?