Since 2002 the European Union (E.U.) summer time rule has been standardized and implemented from the last Sunday in March to the last Sunday in October. The duration of Summer Time varies between 210 days (30 weeks) in some years and 217 days (31 weeks) in others. On transition either way, the clocks in all time zones change simultaneously at 01:00 UTC.
Directive 2000/84/EC of the European Parliament and of the Council of 19 January 2001 on summer-time arrangements
For the purposes of this Directive "summer-time period" shall mean the period of the year during which clocks are put forward by 60 minutes compared with the rest of the year.
From 2002 onwards, the summer-time period shall begin, in every Member State, at 1.00 a.m., Greenwich Mean Time, on the last Sunday in March.
From 2002 onwards, the summer-time period shall end, in every Member State, at 1.00 a.m., Greenwich Mean Time, on the last Sunday in October.