Time Zone Calculator Guide

Understanding time zones is essential for scheduling international calls, meetings, and travel. The UK uses GMT (Greenwich Mean Time) in winter and BST (British Summer Time, GMT+1) from late March to late October, which can cause confusion when coordinating with other countries.

This guide explains UK time, common international time zone conversions, and tips for scheduling meetings across different regions—particularly useful for remote workers and businesses with international clients.

UK Time: GMT vs BST

Common Time Zone Differences from UK

When 12:00 in London...

International Meeting Planning

• UK ↔ US East: 14:00-18:00 UK works for business hours
• UK ↔ US West: 17:00-21:00 UK for their morning
• UK ↔ Asia: Early morning UK for their afternoon
• UK ↔ Australia: Very early/late UK hours needed

UK Clock Change Dates

Remember: "Spring forward, fall back" - clocks go forward in spring (losing an hour of sleep) and back in autumn (gaining an hour).

Major World Cities Time Zones

Best Meeting Times (UK Perspective)

Remote Work Time Zone Tips

• Use UTC: For team scheduling, agree on UTC times to avoid confusion
• Calendar apps: Google Calendar and Outlook automatically convert time zones
• World clock: Add key cities to your phone's world clock
• Be specific: Always state the time zone when scheduling (e.g., "3pm GMT")
• Check DST: Verify both locations' current DST status before booking

24-Hour to 12-Hour Clock

GMT and BST: Understanding UK Time

The United Kingdom operates on two time standards throughout the year. Greenwich Mean Time (GMT), also designated UTC+0, is the UK's standard time used during the winter months. British Summer Time (BST), which is UTC+1, is used during the summer months to provide an extra hour of daylight in the evenings.

GMT is named after the Royal Observatory in Greenwich, London, which served as the reference point for global timekeeping from 1884 when it was established as the prime meridian at the International Meridian Conference in Washington, D.C. While UTC (Coordinated Universal Time) has since replaced GMT as the international standard for civil timekeeping, GMT and UTC are effectively identical for everyday purposes, differing only at the sub-second level due to the way each is calculated.

The distinction between GMT and BST is crucial for scheduling. During BST (late March to late October), the UK is one hour ahead of GMT. This means that a meeting scheduled for "10:00 GMT" during the summer actually takes place at 11:00 UK local time. International communications should always specify whether a time is in GMT, BST, or UTC to avoid ambiguity.

UK Daylight Saving: Changeover Dates and Rules

The UK's clock changes follow rules set under the Summer Time Order 2002, which aligns with the European Union's daylight saving schedule. Despite Brexit, the UK has maintained the same changeover pattern.

Clocks go forward (GMT to BST): The last Sunday in March at 01:00 GMT. In 2025, this falls on 30 March, and in 2026, on 29 March. At 01:00, clocks move forward to 02:00 BST, meaning that day has only 23 hours. The mnemonic "spring forward, fall back" helps remember the direction of the change.

Clocks go back (BST to GMT): The last Sunday in October at 02:00 BST. In 2025, this falls on 26 October, and in 2026, on 25 October. At 02:00 BST, clocks move back to 01:00 GMT, meaning that day has 25 hours. This extra hour means the period between 01:00 and 02:00 occurs twice, which can cause confusion for scheduling and transport timetables.

Most digital devices, including smartphones, computers, and smart watches, adjust automatically. However, analogue clocks, oven timers, car clocks in older vehicles, and wall clocks must be changed manually. It is also worth checking any scheduled alarms, timers, or automated systems after each clock change.

UTC Offsets for Key International Business Centres

For UK-based professionals working with international colleagues, knowing the UTC offset of major business centres is invaluable for scheduling calls and meetings. Note that many of these locations also observe daylight saving time, so the offset from UK time may change at different points in the year.

New York (Eastern Time): UTC-5 in winter (EST), UTC-4 in summer (EDT). This means New York is typically 5 hours behind the UK, but this can temporarily shift to 4 or 6 hours during the brief periods when one country has changed clocks but the other has not yet done so.

Los Angeles (Pacific Time): UTC-8 in winter (PST), UTC-7 in summer (PDT). Los Angeles is 8 hours behind the UK in winter and 7 hours behind in summer, making same-day collaboration challenging.

Dubai (Gulf Standard Time): UTC+4 year-round. The UAE does not observe daylight saving time, so Dubai is 4 hours ahead of the UK in winter and 3 hours ahead during BST.

Singapore (SGT): UTC+8 year-round. Singapore does not observe daylight saving, so it is 8 hours ahead of the UK in winter and 7 hours ahead during BST.

Sydney (Australian Eastern Time): UTC+10 in winter (AEST), UTC+11 in summer (AEDT). Note that Australian summer is during the UK's winter, so the offset ranges from 9 to 11 hours ahead depending on the time of year.

Tokyo (Japan Standard Time): UTC+9 year-round. Japan does not observe daylight saving, making it 9 hours ahead of GMT and 8 hours ahead during BST.

Scheduling International Meetings from the UK

Finding mutually acceptable meeting times across multiple time zones is one of the most common challenges for UK-based international businesses. Here are practical strategies:

For UK-US meetings (Eastern Time), the most productive overlap window is between 13:00 and 17:00 UK time (08:00-12:00 ET). For UK-Asia meetings (Singapore/Hong Kong), early morning UK calls at 08:00-09:00 correspond to 15:00-16:00 in Singapore. For tri-continental meetings spanning the UK, US East Coast, and East Asia, the only workable window is typically 07:00-08:00 UK time (15:00-16:00 SGT, 02:00-03:00 ET), which requires at least one party to meet outside normal business hours.

Frequently Asked Questions

Why does the UK change clocks twice a year?

The UK first adopted daylight saving time in 1916 under the Summer Time Act, following a campaign by builder William Willett who argued that advancing clocks in summer would give people more usable daylight hours. The practice was made permanent after World War I and has continued with minor modifications since. There have been periodic debates about abolishing the clock changes or moving the UK to Central European Time (UTC+1 in winter, UTC+2 in summer), but no change has been implemented. The most recent serious proposal, the Daylight Saving Bill 2010-12, passed its Second Reading in Parliament but did not progress further.

Does the whole of the UK use the same time zone?

Yes. The entirety of England, Scotland, Wales, and Northern Ireland uses GMT in winter and BST in summer. However, the UK's Crown Dependencies (Jersey, Guernsey, and the Isle of Man) and Overseas Territories use different time zones. Gibraltar uses Central European Time (UTC+1/+2), the Falkland Islands use UTC-3, and British Indian Ocean Territory uses UTC+6, among others. When scheduling with contacts in these locations, treat them as separate time zones from mainland UK.

What happens to flight times during clock changes?

Airlines schedule flights in local time for both departure and arrival. When clocks change, the actual flight duration remains the same, but the apparent time difference may change. For example, a London to New York flight departing at 09:00 and lasting 8 hours arrives at 12:00 local time (Eastern) in winter but at 13:00 local time in summer if only the UK has changed clocks. Always check your flight times in the days following a clock change, as some airlines adjust schedules and departure times may shift.

UK Time Zones: History, Law, and International Business

The United Kingdom has a unique relationship with time zones, being the home of the Prime Meridian at the Royal Observatory in Greenwich, London. Greenwich Mean Time (GMT) was established in 1675 and became the global reference point for time in 1884 when the International Meridian Conference in Washington DC designated it as the world's prime meridian. While Coordinated Universal Time (UTC) has technically replaced GMT as the international time standard since 1972, the two are functionally identical for civilian purposes, and the UK continues to use GMT as its winter time zone designation.

British Summer Time (BST) was first introduced during World War I through the Summer Time Act 1916 to save energy by making better use of daylight hours. Clocks advance by one hour on the last Sunday of March and revert on the last Sunday of October. The UK government periodically considers proposals to change the arrangement. Between 1968 and 1971, Britain experimented with permanent BST (effectively GMT+1 year-round), but the trial was abandoned after concerns about darker winter mornings in Scotland and Northern Ireland, where sunrise would not occur until after 10:00 in midwinter. More recently, the EU voted to abolish seasonal clock changes from 2026, but as a post-Brexit UK, Britain is not bound by this decision and has made no plans to change its current system.

For UK businesses operating internationally, time zone management is a critical operational consideration. The UK's position at GMT/UTC+0 (or UTC+1 during BST) places it conveniently between Asian and American business hours. London's financial markets open after Tokyo closes and overlap with New York for several hours each afternoon, contributing to London's position as a global financial centre. Approximately 40 percent of the global foreign exchange market is traded through London, a dominance partly attributable to its time zone advantage. The British Overseas Territories span 11 time zones, from the Pitcairn Islands at UTC-8 to the British Indian Ocean Territory at UTC+6, giving the UK one of the widest time zone footprints of any sovereign nation.

Practical Tips for Managing Time Zones from the UK

• Schedule international meetings using UK afternoon hours. The overlap between UK and US East Coast business hours occurs between 13:00 and 17:00 GMT (14:00 to 18:00 BST). This window allows meetings with US colleagues during their morning. For Asia-Pacific contacts, UK morning meetings before 10:00 GMT correspond to late afternoon in India and early evening in East Asia, providing reasonable meeting times for both parties.
• Be aware of temporary time zone shifts in March and November. The UK and US change their clocks on different dates. The US springs forward on the second Sunday of March, while the UK changes on the last Sunday. During this gap of two to three weeks, the time difference between London and New York is four hours instead of the usual five. A similar discrepancy occurs in November when the US falls back first. Always verify the current offset before scheduling calls during these transitional weeks.
• Use UTC rather than GMT or BST for international coordination. When coordinating across multiple time zones, specifying times in UTC avoids confusion about whether the UK is currently observing GMT or BST. Most professional scheduling tools, flight booking systems, and international standards use UTC. Simply remember that UTC equals GMT in winter and BST minus one hour in summer.

Additional Frequently Asked Questions

Emma Thompson

Senior Content Editor

Emma is a senior content editor with a background in financial journalism. She specialises in making UK regulations and calculator tools understandable for consumers, working closely with qualified professionals to ensure accuracy.