European Summer Time

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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 [1].

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)


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), however Western European Time (WET) is gaining usage in Ireland, the most probable cause of which is the fact that Greenwich is in the UK, and Western European Time is more neutral.


The Russian Federation observes Summer Time and makes the change forward and back on the same dates as the European Union (respectively, on the last Sunday in March and the last Sunday in October) – with the important difference, however, that the changeover on both dates takes place in Russia not at 01.00 UTC as in the rest of Europe, but at 02.00 local time (03.00 local daylight time in October) in each time zone.


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