Time Zones

Western European Summer Time (WEST)

UTC offset: +01:00
Standard offset: +00:00 (WET/GMT)
IANA identifiers: Europe/London, Europe/Lisbon, Europe/Dublin, Atlantic/Canary
Abbreviations: WEST (generic), BST (UK), IST (Ireland)
Population: approximately 80 million
DST period: Last Sunday in March to last Sunday in October

Western European Summer Time advances the WET zone one hour forward to UTC+01:00 during summer. In practice, this means the United Kingdom (calling it BST, British Summer Time), Ireland (calling it IST, Irish Standard Time), Portugal (calling it WEST), the Canary Islands, and the Faroe Islands all move their clocks forward on the last Sunday in March and back on the last Sunday in October.

The naming is confusing. Same offset, different labels depending on the country. The underlying mechanism is identical.

Where It Applies

  • United Kingdom (~67 million): England, Scotland, Wales, Northern Ireland
  • Ireland (~5 million): Republic of Ireland
  • Portugal (~10 million): Mainland and Madeira
  • Canary Islands (~2.2 million): Spanish archipelago off Morocco
  • Faroe Islands (~54,000): Danish autonomy
  • Iceland does NOT observe WEST (stays on UTC+00:00 permanently)

The UK/BST

British Summer Time puts the UK at UTC+01:00, matching Central European Standard Time. This means London is on the same clock as Paris, Berlin, and Madrid during summer (since CET countries advance to CEST/+02:00 simultaneously). Well, actually no. When both shift, the UK goes to +01:00 and CET countries go to +02:00, maintaining the one-hour gap. The UK is never on the same clock as France under the current system.

The longest day in London (June solstice) provides about 16 hours 38 minutes of daylight. Sunset around 9:21 p.m. BST. The shortest day (December solstice) gives about 7 hours 50 minutes, with sunset at 3:53 p.m. GMT. This dramatic 9-hour swing in day length is exactly why DST exists at these latitudes.

Ireland's time law is structured backwards from every other country. Ireland defines IST (UTC+01:00) as its "standard time" and winter time (UTC+00:00) as the deviation. Legally, Ireland doesn't "spring forward" to summer time; it "falls back" from standard to winter time. The practical effect is identical to the UK's system, but the legal framing is inverted. This matters for EU regulatory purposes and causes confusion in legal documents.

Portugal's Return

Portugal was on CET (UTC+01:00) from 1966 to 1976 and again from 1992 to 1996. Both experiments were abandoned because the westerly longitude (Lisbon is at about 9W) made CET absurdly misaligned with solar time. With CET year-round, winter sunrise in Lisbon wouldn't come until after 9:00 a.m. Portugal returned to WET/WEST each time.

The EU Abolition Debate

In 2018, a European Commission consultation found 84% of respondents favored ending biannual clock changes. The European Parliament voted in 2019 to abolish DST by 2021. It never happened. Member states couldn't agree on whether to stay permanently on summer or winter time, COVID-19 diverted political attention, and the proposal has been effectively shelved.

If the UK (post-Brexit) or EU countries ever did adopt permanent summer time:

  • London at permanent +01:00: December sunrise at ~9:03 a.m., sunset at ~4:53 p.m.
  • Lisbon at permanent +01:00: December sunrise at ~8:52 a.m.

The dark mornings make this politically difficult at northerly latitudes.

Business Impact

WEST/BST creates the annual shift in transatlantic scheduling. When both Europe and North America are on summer time, London-New York is 5 hours. But the transition dates differ (Europe: last Sunday March/October; US: second Sunday March, first Sunday November). For 2-3 weeks in March and 1 week in October/November, the gap temporarily narrows to 4 hours. This trips up international scheduling every spring and autumn.

Scheduling (During WEST/BST)

At UTC+01:00:

  • Paris/Berlin (CEST, +02:00): 1 hour ahead
  • New York (EDT, -04:00): 5 hours behind
  • Los Angeles (PDT, -07:00): 8 hours behind
  • Tokyo (+09:00): 8 hours ahead
  • Dubai (+04:00): 3 hours ahead
  • Sydney (AEST, +10:00): 9 hours ahead

Technical Identifiers

  • Europe/London (IANA, UK)
  • Europe/Dublin (IANA, Ireland)
  • Europe/Lisbon (IANA, Portugal)
  • Atlantic/Canary (IANA, Canary Islands)
  • BST (British Summer Time)
  • IST (Irish Standard Time, conflicts with India Standard Time)
  • WEST (Western European Summer Time)
  • Windows: "GMT Standard Time" (covers both GMT and BST)
  • DST rule: Last Sunday March to last Sunday October

Quick Reference

Attribute Value
UTC offset +01:00
Active period Late March to late October
Standard offset +00:00 (WET/GMT)
Population ~80 million
Key countries UK, Ireland, Portugal
UK name BST (British Summer Time)
Ireland name IST (Irish Standard Time)
EU abolition status Stalled since 2019
London-NY gap 5 hours (during mutual summer time)