Western European Summer Time (WEST) is a summer daylight saving time scheme, 1 hour ahead of Greenwich Mean Time and Coordinated Universal Time. It is used in:
- the Canary Islands
- Portugal (including Madeira but not the Azores)
- the United Kingdom
- the British Crown dependencies
- the Faroe Islands
Western European Summer Time is known in the countries concerned as:
- British Summer Time (BST) in the United Kingdom.
- Irish Standard Time (IST) (ACÉ)) in Ireland. Also sometimes erroneously referred to as "Irish Summer Time".
The scheme runs from the last Sunday in March to the last Sunday in October each year. At both the start and end of the schemes, clock changes take place at 01:00 UTC+00:00. During the winter, Western European Time (WET, GMT+0 or UTC±00:00) is used.
The start and end dates of the scheme are asymmetrical in terms of daylight hours: the vernal time of year with a similar amount of daylight to late October is mid-February, well before the start of summer time. The asymmetry reflects temperature more than the length of daylight.
Ireland observes Irish Standard Time during the summer months and changes to UTC±00:00 in winter. As Ireland's winter time period begins on the last Sunday in October and finishes on the last Sunday in March, the result is the same as if it observed summer time.
- Eastern Time Zone (North America)
- Central Daylight Time Zone
- Pacific Daylight Time
- Greenwich Mean Time
- British Summer Time
- Moscow Time