European Summer Time

European Summer Time is the arrangement in Europe by which clocks are advanced by one hour in Spring to make the most of seasonal daylight. This is done in all of the countries of Europe except Iceland which observes GMT all year round. In the European Union this period extends from 01.00 GMT on the last Sunday in March until 01.00 GMT on the last Sunday in October each year.

1 History
2 Exact timing in the next several years
3 Local observations
4 See also
5 References
6 Further reading

Time zones of Europe:

blue	Western European Time (UTC+0) Western European Summer Time (UTC+1)
red	Central European Time (UTC+1) Central European Summer Time (UTC+2)
yellow	Eastern European Time (UTC+2) Eastern European Summer Time (UTC+3)
green	Moscow Time (UTC+3) Moscow Summer Time (UTC+4)

Light colours indicate countries that do not observe summer time: Algeria, Iceland and Morocco

History

Historically the countries of Europe had different practices for observing summer time, but this hindered coordination of transport, communications and movements. In the 1980s the European Community began issuing directives requiring member states to legislate particular start and end dates for summer-time.

Since 1981 each directive has specified a transition time of 01:00 UTC and a start date of the last Sunday in March, but the end dates have differed. In 1981 and 1982 the end dates were the fourth Sunday in October. In 1983 the end date was changed to the last Sunday in September for all time zones other than Western European Time. In 1996 the end date for all time zones was changed to the fourth Sunday in October. In 1998 the end date was adjusted to be the last Sunday in October; this happened to be the same as the previous rule for 1996 and 1997.^[1] The ninth directive, currently in force, has made this permanent.^[2]

Exact timing in the next several years

European Summer Time begins (clocks go forward) at 01.00 GMT on

Formula used to calculate the beginning of European Summer Time:

Sunday (31 - (5y ÷ 4 + 4) mod 7) March at 01.00 GMT

(valid through 2099^[3]), where y is the year, and for the nonnegative a, a mod b is the remainder of division after truncating both operands to an integer.

European Summer Time ends (clocks go backward) at 01.00 GMT on

Formula used to calculate the end of European Summer Time:

Sunday (31 - (5y ÷ 4 + 1) mod 7) October at 01.00 GMT

(validity as above).

For today these formulae yield a daylight saving time offset of 0 (1 = summer time).^[4]

Local observations

In most of Europe the word Summer is added to the name of each European time zone during this period: thus, in the GMT+1 time zone, Central European Time becomes Central European Summer Time (GMT+2).

In the United Kingdom local time during this period is known as British Summer Time (BST) while local time during the rest of the year is normally referred to as Greenwich Mean Time (GMT).

In Ireland, local time during this period is known as "IST", which officially stands for "Irish Standard Time", not "Irish Summer Time". Ireland's official timezone is CET (UTC+1), but this only applies during the summer (when areas in Europe that use CET are in CEST), with clocks being moved back one hour for winter time (known variously in the country as WET, UTC or GMT).

Western Europe

All parts of Western Europe (except Iceland), whether or not in the EU, use the EU rules for both the date and the time of their clock changes.

Russia & Belarus

Russia and Belarus observe Summer Time and make 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 GMT as in the rest of Europe, but at 02.00 local time (= 03.00 local daylight-saving time in October) in each time zone.

Turkey

Turkey observes the EU rules for both the date and the time of its clock changes.

References

^ Joseph Myers (2007-01-21). "History of legal time in Britain". Retrieved on 2007-03-24.
^ "Directive 2000/84/EC of the European Parliament and of the Council of 19 January 2001 on summer-time arrangements".
^ Attributed to Robert H. van Gent. "Daylight Saving Time: About this exhibit"
^ This number is automatically computed by the Mediawiki software by checking whether today's date falls within the interval specified by the above formulae.