Abidjan runs on the same clock in January and July. No spring forward, no fall back. That is Greenwich Mean Time in practice: a fixed offset, UTC+0, that stays put while half the world shifts around it.
GMT is not "UK time." The United Kingdom uses GMT only in winter. From late March to late October, British clocks move to British Summer Time (UTC+1). The zone itself never moves. That distinction causes more missed meetings and bungled flight bookings than any other time zone confusion, and it is worth getting right before you send the calendar invite.
What Is the Current GMT Offset?
GMT is always UTC+0. It does not observe daylight saving time in 2026 or 2027. The offset stays flat through both solstices and both equinoxes.
The IANA zone for the fixed offset is Etc/GMT. Do not use Etc/GMT+0 or Etc/GMT-0: the POSIX sign convention in the Etc area reverses the sign, so Etc/GMT-5 means UTC+5. Etc/GMT is the unambiguous choice.
Which Places Use GMT All Year?
Seven IANA zones belong to the CLDR metazone that carries the GMT abbreviation. They span West Africa, the North Atlantic and Antarctica.
| Zone | Country or territory |
|---|---|
| Africa/Abidjan | Ivory Coast |
| Africa/Bissau | Guinea-Bissau |
| Africa/Monrovia | Liberia |
| Africa/Sao_Tome | São Tomé and Príncipe |
| America/Danmarkshavn | Greenland (Danmarkshavn) |
| Antarctica/Troll | Troll station, Antarctica |
| Etc/GMT | Fixed offset (no country) |
Cities on GMT
The largest population centres in the zone are in Ivory Coast. Abidjan (population 6,321,017) and Abobo (1,340,083) both use Africa/Abidjan. Monrovia, Liberia (1,542,549) uses Africa/Monrovia. Bissau, Guinea-Bissau (439,704) uses Africa/Bissau.
Other Ivorian cities on the zone include Bouaké (832,371), Korhogo (440,926), Daloa (421,871), Koumassi (412,282), San-Pédro (390,654), Gagnoa (277,044), Yamoussoukro (275,686), Sinfra (245,226), Man (241,969), Marcory (214,061) and Bondoukou (141,568).
Why Doesn't Ivory Coast Have Daylight Saving?
Proximity to the equator makes clock changes pointless. Abidjan, at 5.354° N, sees roughly 12 hours of sun every day of the year. The June solstice stretches it to 12 hours 26 minutes. The December solstice shrinks it to 11 hours 49 minutes. That 37-minute swing is too small to justify moving clocks twice a year.
Abidjan: Sunlight Through the Year
Abidjan sits at coordinates 5.354, -4.002, elevation 50 metres. Its sunrises and sunsets barely shift.
March Equinox (20 March 2026)
Sunrise 06:20, sunset 18:27. 12 hours 6 minutes of sunlight.
June Solstice (21 June 2026)
Sunrise 06:04, sunset 18:30. 12 hours 26 minutes of sunlight. The longest day of the year.
September Equinox (22 September 2026)
Sunrise 06:05, sunset 18:12. 12 hours 7 minutes of sunlight.
December Solstice (21 December 2026)
Sunrise 06:19, sunset 18:08. 11 hours 49 minutes of sunlight. The shortest day of the year.
GMT Offsets Around the World
The gap between GMT and another city depends on the date. Summer time in North America and Europe widens or narrows the difference. These offsets are relative to GMT (UTC+0).
15 January 2026
| City | Offset from GMT |
|---|---|
| London | Same time |
| Paris | +1 hour |
| Johannesburg | +2 hours |
| Dubai | +4 hours |
| Mumbai | +5.5 hours |
| Singapore | +8 hours |
| Tokyo | +9 hours |
| Sydney | +11 hours |
| São Paulo | -3 hours |
| New York | -5 hours |
| Chicago | -6 hours |
| Los Angeles | -8 hours |
15 July 2026
| City | Offset from GMT |
|---|---|
| London | +1 hour |
| Paris | +2 hours |
| Johannesburg | +2 hours |
| Dubai | +4 hours |
| Mumbai | +5.5 hours |
| Singapore | +8 hours |
| Tokyo | +9 hours |
| Sydney | +10 hours |
| São Paulo | -3 hours |
| New York | -4 hours |
| Chicago | -5 hours |
| Los Angeles | -7 hours |
London and Paris shift. Johannesburg, Dubai, Mumbai, Singapore, Tokyo, and São Paulo do not. Sydney moves from +11 to +10 because the southern hemisphere summer ends. New York, Chicago and Los Angeles each gain an hour relative to GMT as North American summer time kicks in.
Who Uses GMT as a Reference?
Aviation and the Military
Flight plans, NOTAMs and air traffic control everywhere use UTC. The military calls it Zulu time. A timestamp ending in "Z" means UTC. No conversion, no DST confusion.
Maritime
Ships' logs and navigation systems run on UTC. The prime meridian at Greenwich is 0° longitude, the baseline for every nautical chart.
Computing
Servers overwhelmingly run on UTC. Unix timestamps count seconds since 1970-01-01 00:00:00 UTC. Setting a server to local time with DST creates bugs that are hard to reproduce and harder to fix.
Finance
Forex markets quote session opens in GMT. The London session opens at 08:00 GMT in winter. In summer London is on BST, but the market reference stays GMT. Check which convention your counterparty uses before trading around the clock change.
Broadcasting
The BBC World Service publishes schedules in GMT. International sports events often announce kick-off times in GMT. Formula 1 session times appear in local time plus GMT.
Science
Astronomers and meteorologists log observations in UTC. Amateur radio operators do the same for contacts.
Is GMT the Same as UTC?
GMT and UTC read the same on a clock. They are not the same thing.
GMT was originally an astronomical standard: mean solar time at the Royal Observatory, Greenwich. The Earth's rotation determines it. UTC is an atomic standard, maintained by the International Bureau of Weights and Measures in Paris. Caesium clocks define it.
The Earth's rotation is not perfectly steady. Tidal friction slows it. UTC stays aligned with astronomical time through leap seconds, decided by the International Earth Rotation and Reference Systems Service. The gap between UTC and UT1 (the modern astronomical measure) is kept below 0.9 seconds.
For civilian use the distinction rarely matters. For software, aviation and scientific work, "UTC" is the precise term. "GMT" persists in UK law, maritime tradition and common speech.
Why Does the UK Change Clocks?
The United Kingdom runs on GMT from the last Sunday in October to the last Sunday in March. British Summer Time (UTC+1) covers the rest of the year.
Clocks go forward: last Sunday in March at 01:00 GMT, becoming 02:00 BST. Clocks go back: last Sunday in October at 02:00 BST, becoming 01:00 GMT.
The Summer Time Act 1972 defines BST as "one hour in advance of Greenwich mean time." That wording keeps GMT in UK law even when the country is not using it.
The Willett Proposal
William Willett, a builder, published "The Waste of Daylight" in 1907. His argument: summer mornings were wasted while evenings were dark. He proposed an 80-minute shift in 20-minute weekly steps. Parliament did not adopt the scheme in his lifetime. Willett died in 1915.
Germany adopted summer time in 1916 to conserve fuel. Britain followed weeks later with the Summer Time Act 1916.
Double Summer Time
During the Second World War, Britain ran on GMT+1 in winter and GMT+2 in summer. The arrangement lasted from 1941 to 1945 and returned briefly in 1947 during a fuel crisis.
The 1968-1971 Experiment
From 27 October 1968 to 31 October 1971, the UK stayed on BST year-round. The government wanted to test whether permanent summer time would cut road casualties and energy use. Scotland objected. Dark mornings meant children travelled to school before sunrise. The experiment ended and the UK reverted to the winter GMT, summer BST pattern.
How Did Greenwich Mean Time Become the World's Reference?
Before Standard Time
Towns set their clocks by the sun. Bristol sat roughly 10 minutes behind London. When the Great Western Railway adopted "London Time" in 1840, passengers had to adjust their watches at every station. Some stations put up two clocks: one for railway time, one for local time.
The railways forced the issue. Timetables written in multiple local times caused collisions. By 1847 the Railway Clearing House recommended all companies adopt London Time. Most complied by 1848.
The Statutes (Definition of Time) Act 1880
Parliament made GMT the legal time for Great Britain in 1880, four years before the global conference that would internationalise it. The act swept away the patchwork of local times that persisted outside the rail network.
The 1884 International Meridian Conference
Twenty-five nations met in Washington DC in October 1884. The task: pick a prime meridian and a universal day. Greenwich won. Twenty-two nations voted for it. France abstained. The resolution placed the zero-degree longitude line through the transit instrument at the Royal Observatory.
The conference also settled that the universal day would begin at mean midnight at Greenwich. Astronomers had previously started their day at noon. The shift to midnight aligned astronomical practice with civil timekeeping in 1925.
The Move to Atomic Time
The second was redefined in 1967 using caesium atomic resonance. In 1972 Coordinated Universal Time replaced astronomical GMT as the world's time standard. Leap seconds keep UTC within 0.9 seconds of Earth rotation. GMT became a time zone: UTC+0.
What Mistakes Do People Make With GMT?
Calling UK Local Time "GMT" in Summer
From late March to late October, the UK is on BST, not GMT. Saying "let's meet at 14:00 GMT" when you mean "14:00 UK local time" in July puts the meeting an hour early. Specify "GMT" or "UTC" and let the other person convert.
Assuming GMT Observes Daylight Saving
GMT is fixed at UTC+0. The United Kingdom observes daylight saving. The zone does not.
Thinking All of Africa Changes Clocks
West African nations on GMT do not shift. Near-equatorial sun is too consistent to justify it.
Confusing Etc/GMT+X Signs
Etc/GMT-5 means UTC+5. The POSIX convention reverses the sign. Etc/GMT is the safe zone for UTC+0.
Writing "Greenwich Meridian Time"
The correct expansion is Greenwich Mean Time. "Mean" refers to mean solar time, not the meridian.
What Do GMT, UTC and Zulu Time Mean?
Greenwich Mean Time (GMT): Mean solar time at the Royal Observatory, Greenwich. Now used to mean UTC+0.
Coordinated Universal Time (UTC): Atomic time standard maintained by the BIPM. Basis for civil time worldwide.
Prime Meridian: 0° longitude, passing through Greenwich.
Zulu time (Z): Military and aviation term for UTC.
British Summer Time (BST): UK daylight saving time, UTC+1.
Western European Time (WET): Same offset as GMT. Used in Portugal, and by Ireland and Iceland. Check local legislation for Irish terminology.
Leap second: One-second adjustment to UTC, decided by the IERS, to track Earth's rotation.
UT1: Astronomical time based on Earth's actual rotation.
TAI (International Atomic Time): Atomic time without leap seconds. UTC = TAI minus accumulated leap seconds.
IANA time zone database: Maintained by the IETF. Defines zones including Etc/GMT and Europe/London.
CLDR metazone: Groups zones sharing abbreviation and offset behaviour. The GMT metazone covers Africa/Abidjan, Etc/GMT and others.
Who Governs GMT and UTC?
Royal Observatory, Greenwich: Historic home of the prime meridian. Now a museum.
National Physical Laboratory (NPL): UK official timekeeper. Operates atomic clocks.
BIPM (Bureau International des Poids et Mesures): Maintains UTC in Paris.
IERS (International Earth Rotation and Reference Systems Service): Decides leap seconds.
ITU (International Telecommunication Union): Sets radio time signal standards.
For the current time in GMT, see the GMT Time Now page. For the difference between GMT and UTC, see GMT vs UTC. For GMT versus British Summer Time, see GMT vs BST.