European Summer Time is the daylight saving time practised in Europe, the period during which clocks are advanced by one hour in relation to the official time observed during the rest of the year.
This is done in all of the countries of Europe except Iceland (which observes UTC all year round), and has also been prescribed by a directive of the European Union.
This period extends from 01.00 UTC on the last Sunday in March until 01.00 UTC on the last Sunday in October each year.
Exact timing in the next several years
European Summer Time begins (clocks go forward) at 01.00 UTC on
Equation used to calculate the beginning of European Summer Time:
Sunday (31 - (5*y/4 + 4) mod 7) March at 01.00 UTC
(valid through 2099, courtesy of Robert H. van Gent, EC)
European Summer Time ends (clocks go back) at 01.00 UTC on
Equation used to calculate the end of European Summer Time:
Sunday (31 - (5*y/4 + 1) mod 7) October at 01.00 UTC
(validity and credits as above)
Terminology
In most of Europe the word Summer is added to the name of each European time zone during this period: thus, in the UTC+1 time zone, Central European Time becomes Central European Summer Time (UTC+2).
In the United Kingdom local time during this period is known as British Summer Time (BST), in Ireland as Irish Summer Time (IST), while in both countries local time during the rest of the year is normally referred to as Greenwich Mean Time (GMT).
External link