Convert UTC to GMT Coordinated Universal Time ↔ Greenwich Mean Time Free Online Secure
Coordinated Universal Time and Greenwich Mean Time read the same on the clock — the offset is zero. Type a time in UTC and it comes back unchanged in GMT, which is the honest answer; what differs between the two names is explained below.
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Through the day — Convert UTC to GMT (Coordinated Universal Time ↔ Greenwich Mean Time)
| UTC | GMT |
|---|---|
| 00:00 | 00:00 |
| 03:00 | 03:00 |
| 06:00 | 06:00 |
| 09:00 | 09:00 |
| 12:00 | 12:00 |
| 15:00 | 15:00 |
| 18:00 | 18:00 |
| 21:00 | 21:00 |
Where these units come from
Until the middle of the nineteenth century every town kept its own noon, set by the sun overhead, and nobody minded that the next town was four minutes behind. Railways ended that: a timetable cannot be written for a hundred local noons. Britain put its railways on Greenwich time in 1847, and in 1884 the International Meridian Conference in Washington chose Greenwich as the prime meridian and sketched the twenty-four-hour scheme we still use. Greenwich Mean Time was the world's reference until 1972, when Coordinated Universal Time replaced it: UTC is kept by atomic clocks and tied back to the turning Earth by leap seconds. The abbreviations on this page name standard time — the winter setting — which is why each one is a fixed number of hours rather than something that drifts through the year.
Where you meet them
A time zone becomes real the moment two people in different places have to agree on one moment: a call between offices, a flight that lands before it took off, a market that opens while you are asleep, a deadline written in somebody else's afternoon. Server logs, train and flight schedules and anything stamped with a time are kept in UTC precisely so that the question can always be settled, no matter whose clock was on the wall.
Questions people ask
What about summer time?
The offsets here are standard-time offsets, the ones a zone keeps in winter. Where summer time is observed, the same places move one hour further on for part of the year and take a different name: Central European Time becomes Central European Summer Time, Eastern Standard Time becomes Eastern Daylight Time. The switching dates are not the same in every country, and the two hemispheres change in opposite months, so for a date inside a summer-time period add an hour to whichever side observes it.
Why isn't every difference a whole number of hours?
Because offsets are decided by governments, not by geometry. India is half an hour off the hour, at UTC+05:30; Nepal is three quarters, at UTC+05:45; the Chatham Islands are at UTC+12:45. Any of these can be changed by law, and several countries have moved their offset within living memory.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Two labels, one clock
You meet both names in a single morning. A flight confirmation says departure at 06:40 GMT, a spreadsheet export is stamped in UTC, and a build log from a cloud server ends with 09:12:30Z. Naturally you wonder whether the labels hide a gap that needs adding or subtracting. They do not. To convert UTC to GMT, you keep the clock reading exactly as it is: 06:40 UTC is 06:40 GMT, and 09:12 UTC is 09:12 GMT. The offset between them is zero hours, zero minutes, and the calendar date never moves.
The difference lies elsewhere, in how each name is defined and in a long list of habits that grew up around them. The page below explains that difference and how to convert UTC to GMT correctly, shows a handful of worked readings, lists the places where each label still dominates, and warns about the one trap that catches people every year: London is on Greenwich Mean Time only in winter. The arithmetic runs in your browser, and nothing you type is sent to a server.
The rule in plain numbers
Copy the time, keep the date
Both scales sit at offset +00:00. Whenever you convert UTC to GMT, there is nothing to add and nothing to subtract. Write down the hours and minutes you started with. A reading of 00:05 UTC becomes 00:05 GMT on the same calendar day, and 23:59 UTC becomes 23:59 GMT on the same calendar day. No midnight is crossed.
Four quick examples
Nine in the morning UTC is nine in the morning GMT. Noon UTC is noon GMT. A server job that fires at 04:15 UTC fires at 04:15 GMT. A certificate printed with the expiry 18:00:00 GMT expires at 18:00:00 UTC, which is what you get when you convert UTC to GMT. In every case the two numbers match to the second.
What the converter cannot know
A converter only knows the two scales you picked. It does not know where you live. If you want the time on a wall clock in Manchester in July, you need British Summer Time, which is UTC+1, and that is a different conversion. The same applies to Bucharest, New York or Mumbai: UTC and GMT both stand still, and local clocks move around them.
What UTC is
A compromise name
Coordinated Universal Time is the reference that every civil clock in the world is measured against. Its abbreviation is a diplomatic compromise. English speakers wanted CUT for “coordinated universal time”, French speakers wanted TUC for “temps universel coordonné”, and the International Telecommunication Union settled on UTC, which belongs to neither language.
Built from atomic clocks
UTC is computed by the International Bureau of Weights and Measures near Paris from a few hundred atomic clocks kept in about eighty national laboratories. The second it counts is the atomic second, defined by the radiation of caesium atoms. Because Earth’s spin is slightly irregular, UTC is nudged by leap seconds so that it never drifts more than 0.9 seconds from the Sun-based scale. Twenty-seven of them have been added since 1972, and the most recent was at the end of 2016.
Where you will see it
UTC is the working language of computing, aviation, astronomy and telecommunications. Network time servers distribute it, databases store it, and satellites broadcast it. Whenever a technical document avoids naming a city, the time in it is almost always UTC.
What GMT is
Born at an observatory
Greenwich Mean Time was the mean solar time at the Royal Observatory in Greenwich, east London. Averaged over a year, the Sun crossed that meridian at noon. British railways adopted it in the 1840s so that timetables could agree from one town to the next, and an 1880 Act of Parliament made it the legal time of Great Britain. In 1884 an international conference in Washington chose the Greenwich meridian as the zero line of longitude for everybody.
A day that once began at noon
For astronomers, a GMT day used to start at noon rather than midnight, a convention that lasted until the end of 1924. Navigators had kept it because it avoided changing the date in the middle of a night’s observations. After 1925 the day started at midnight, as it does for the rest of us.
Where you will see it
Today GMT is the legal winter time in the United Kingdom and a year-round clock in Iceland, Ghana, Senegal and a few neighbours. It also survives as a fixed label in web protocols and in the daily time signal known as the pips, broadcast by the BBC since 1924.
Putting the two side by side
Why the difference does not matter for the clock
One scale is counted by atoms, the other was originally read from the Sun, yet the two never differ by as much as a second. A calendar, a train ticket, a deadline or a log line cannot tell them apart. That is why dictionaries, standards bodies and most software treat GMT and UTC as interchangeable when they appear as a time zone label, and why you can convert UTC to GMT with confidence.
Where a purist would object
Scientists use UT1 for the true angle of Earth’s rotation, UTC for the civil clock and TAI for a continuous atomic count with no leap seconds. In that vocabulary GMT is a legacy term. If you write a research paper, use UTC. If you write a ticket or a message to a colleague, GMT is perfectly understood, and you can convert UTC to GMT in your head.
The same moment, eight ways
00:00 UTC is 00:00 GMT. 03:30 UTC is 03:30 GMT. 06:40 UTC is 06:40 GMT. 09:12 UTC is 09:12 GMT. 12:00 UTC is 12:00 GMT. 15:45 UTC is 15:45 GMT. 18:00 UTC is 18:00 GMT. 23:59 UTC is 23:59 GMT.
The British trap: summer time
UTC never changes its clock
UTC has no daylight saving. A reading in January and a reading in July mean exactly what they say. That constancy is the whole reason programmers use it.
Britain does change
The United Kingdom moves its clocks forward by an hour at 01:00 UTC on the last Sunday of March and back again at 01:00 UTC on the last Sunday of October. In 2026 those dates are 29 March and 25 October. Between them, London runs on British Summer Time, UTC+1, and for that stretch “London time” is not GMT even though people still say it is.
A practical test
If the source is a machine, a protocol, a certificate or a scientific schedule, GMT means UTC and you copy the time. If the source is a person describing a meeting in London during the summer, ask whether they mean the clock on the wall. In that case subtract one hour to get UTC.
Why web headers say GMT
A label frozen in 1990s standards
HTTP requires dates in the form Tue, 13 Oct 2026 09:00:00 GMT. The same shape appears in Date, Last-Modified and Expires headers and in the expiry attribute of cookies. The standard was written when GMT was the everyday name for world time, and it kept the letters even after UTC replaced it in science. Every browser reads them as UTC.
Seeing it yourself
Open the developer tools, look at any response, and you will find a header that ends in GMT. Compare it with the log on the server: the clock readings will agree. A difference of one or two hours means somebody has applied a local time zone in between, not that GMT and UTC differ.
OpenSSL and certificates
Validity written in GMT
When you run openssl x509 -dates against a certificate, the output looks like notAfter=Oct 13 09:00:00 2026 GMT. The certificate itself stores the instant in UTC, using a compact encoding, and the tool prints the label GMT for readers. If your monitoring alerts at 09:00 UTC, you do not need to adjust anything to match it.
The renewal window
Administrators who renew a certificate “on the expiry day” should remember that the day ends at 23:59:59 UTC, which is 02:59:59 the next morning in Bucharest in summer and 01:59:59 in winter. The label is harmless, but the local clock decides when the deadline feels real. Run the converter first, then add the local offset.
Email headers
Numeric offsets win
A mail message carries a Date field, and modern software writes it with a numeric offset, such as Date: Tue, 13 Oct 2026 09:00:00 +0000. The older RFC syntax still allows the names GMT and UT. All three mean the same instant. A mail client then converts to your local zone for display.
A detail worth knowing
You may sometimes see -0000 instead of +0000. That is a convention meaning “the sender’s local zone is unknown, but this is UTC”. It does not change the time. When you convert UTC to GMT for a message, the number in the header is already what you want.
Programming languages and databases
Python, JavaScript and SQL
In Python you build an aware timestamp with datetime.now(timezone.utc). In JavaScript, toISOString() always returns UTC, and toUTCString() returns it with the suffix GMT. In PostgreSQL, a timestamp with time zone is stored internally as UTC, and SET TIME ZONE 'UTC' makes the output match. None of these distinguishes between GMT and UTC as an offset.
Names that mislead
The tz database has zones called Etc/GMT+5 and Etc/GMT-14. Their signs are inverted on purpose: Etc/GMT+5 is UTC−5, and Etc/GMT-14 is UTC+14, the clock used on Kiritimati in the Pacific. Do not read the plus sign the way you would on a ticket. For a real place, always pick a city zone such as Europe/London.
The International Space Station
One clock for many nations
The International Space Station is run by agencies in the United States, Russia, Europe, Japan and Canada, and it needs a single schedule. Crews operate on GMT, which the agencies treat as UTC. Orbits last about 92 minutes, so the crew sees an orbital sunrise every hour and a half, and a fixed ground-based clock keeps the daily routine intact.
Launch times you will read
Press releases for launches often quote an Eastern or Pacific time first and a GMT time second. Translating the GMT value to a local clock takes one extra step after you convert UTC to GMT: Bucharest is UTC+2 in winter and UTC+3 in summer, Madrid is UTC+1 and UTC+2, and Delhi is UTC+5:30 all year.
The pips and the BBC
Six short tones
The Greenwich Time Signal, nicknamed the pips, has been broadcast on BBC radio since 1924. It consists of six brief tones, the last of which marks the exact top of the hour. In winter the signal agrees with GMT. In summer it marks British Summer Time, so the pips are not a GMT broadcast during those months.
What listeners learn
The pips show well how the name GMT stuck in public speech. Many people say “GMT” when they mean the time in Britain, which is correct in winter and off by one hour in summer. That habit is the root of most of the confusion this page tries to remove.
Trading hours in the City of London
An example with clocks that move
The London Stock Exchange runs its main trading session from 08:00 to 16:30 London time. In winter, that is 08:00 to 16:30 UTC. In summer, when London is one hour ahead, the same session is 07:00 to 15:30 UTC. If your notes say “opens at 08:00 GMT” in July, the exchange is already open an hour earlier than the label suggests.
Why traders prefer UTC
Global desks record every order in UTC. A trade stamped 14:30:00 UTC means the same instant in New York, Frankfurt and Singapore, and nobody has to remember which of the three has changed its clock that week.
Network time and leap seconds
NTP speaks UTC
The Network Time Protocol keeps computers within milliseconds of UTC. When a device synchronises, it takes a UTC value from a nearby server and then displays it in the local zone. No GMT conversion is involved, although operating systems label the clock “GMT” in a few menus.
Leap seconds and smearing
When a leap second is inserted, the last minute of the day has 61 seconds. Some operators “smear” the extra second across several hours so that software never sees 23:59:60. The standards bodies voted in 2022 to stop adding leap seconds by 2035, which will make UTC steadier and simplify exactly this kind of work.
The countries that stay on GMT all year
Africa and Iceland
Iceland sits on UTC+0 throughout the year, even though it lies far west, and it has no daylight saving. So do Ghana, Senegal, Mali, Guinea and Côte d’Ivoire. For travellers to these countries, the wall clock is the same as the server clock, and they can keep one watch for both.
Europe’s western edge
Portugal, Ireland and the United Kingdom use UTC+0 only in winter. In summer they move to UTC+1, and the label changes with them, even if informal speech does not.
Working with American colleagues
Two ways to describe a gap
New York is five hours behind UTC in winter (EST, UTC−5) and four hours behind in summer (EDT, UTC−4). A call at 14:00 GMT is at 09:00 in New York in January. In the three weeks between the US spring change on 8 March 2026 and the British one on 29 March, the same call at 14:00 UTC is at 10:00 in New York, because the US has moved but Britain has not.
Why keep UTC as the pivot
Fix the meeting in UTC, publish it in UTC, and let each person convert to the local zone. After you convert UTC to GMT, the extra step is the same for everybody, and nobody has to guess which calendar the organiser was looking at.
Reading a time zone map
What the zero column shows
On a standard time zone map the central band that runs from the Arctic to the Antarctic is labelled UTC±0 or GMT. It covers the western part of Europe, the Atlantic islands and a long strip of West Africa. The band is only a convention; the legal clocks in each country decide which zone it uses.
Why the band is crooked
Spain, whose capital Madrid lies west of the Greenwich meridian, uses Central European Time, an hour ahead of the zero band, and so does France. The reasons are historical and political, and they remind us that time zones follow borders and decisions, not just geography.
Shift workers and handovers
A support team in three places
A follow-the-sun support desk might hand over from Singapore at 08:00 UTC to Dublin and then to Austin. The rota is written in UTC so it never changes with the seasons. Staff in Dublin see their handover move by an hour in October, while the rota itself stands still. Anyone who labels the rota “GMT” is giving the same information, as long as the label is not read as the clock in Dublin.
A simple rule for rotas
Write the shift in UTC, add the local equivalent in brackets for each site, and update the brackets in spring and autumn. Do not change the base line.
Aviation: Zulu time
The letter Z
Pilots call UTC Zulu time, after the phonetic word for the letter Z. A forecast issued at 1200Z means 12:00 UTC. Flight plans, weather reports and airspace notices all use this convention so that crews from any country read the same hour. A passenger who sees 0840Z on a technical document can treat it as 08:40 GMT.
Landing times on tickets
Your own boarding pass shows local times at the departure and arrival airports. The aircraft’s flight data uses Zulu. When you compare the two, the gap is simply the local offset at each end on that date.
Daylight saving is a political decision
Rules that change
Governments alter their daylight saving rules from time to time. The European Union has debated ending clock changes for years, and the United States has considered making summer time permanent. UTC is the one stable column, which is why long-lived systems store it. When laws change, data stored in UTC stays correct, while data stored in local time may need repair.
What this means for your notes
If you are archiving timestamps that need to be read in ten years, write them in UTC with the Z suffix. A reader then needs no table of historical rules to understand what you meant.
Hand-checking the result
A thirty-second test
Pick one reading, say 07:20 UTC. Look at a trusted clock set to GMT, such as the one on a time-and-date site or a system tool, and compare it with a clock set to UTC. They agree. Now ask yourself whether a human being in London said the time. If so, check the date: from 29 March to 24 October 2026 the Londoner’s clock is an hour ahead.
Why the test is enough
Nearly every mistake when people convert UTC to GMT comes from the Londoner’s summer clock, not from UTC or GMT themselves. Once you have separated the two ideas, you can convert UTC to GMT without further worry.
A checklist before you convert UTC to GMT
Questions to ask first
Who produced the time?
A machine, a protocol or a scientific schedule gives you a reading that already is UTC, whatever it calls itself. A person describing a meeting in London may be describing a wall clock. Settle that before you convert UTC to GMT, and the answer is straightforward in both cases.
Which date applies?
The date decides whether London is on GMT or BST. In 2026 the window is 29 March to 24 October. Outside it, a Londoner’s wall clock and GMT agree. Inside it, they are an hour apart.
After the conversion
What the result should look like
The hours and minutes should be identical to the input and so should the date. If either has changed, you have performed some other conversion by mistake. Correct output when you convert UTC to GMT is always the same clock reading.
How to write it down
State the label you chose once, either UTC or GMT, and add the date. In technical notes prefer UTC. In a message to a friend, GMT is fine. In a contract, give the offset as +00:00 and avoid the city.
Spreadsheets, shells and scripts
Everyday tools that do this for you
In a spreadsheet, the formula =A1 is all you need to convert UTC to GMT, because the offset is zero. In a Linux shell, running TZ=UTC date and TZ=GMT date prints the same clock reading with different labels. In SQL, AT TIME ZONE 'UTC' and AT TIME ZONE 'GMT' return identical values. In Python, ZoneInfo('GMT') resolves to a fixed zero offset, just as timezone.utc does.
A ten-second experiment
Run the two shell commands one after the other and compare the output. The hours and minutes match, and only the abbreviation at the end differs. It is the quickest proof that a request to convert UTC to GMT changes nothing but the label.
Why phones and apps show “GMT+0”
Labels chosen by software
Operating systems choose their own label. Some show UTC, some show GMT, some show a bare Z, and some show GMT+0 in the time zone picker. The clock behind each is the same. That variety is one reason so many people look up how to convert UTC to GMT even though the answer is that nothing needs to change.
Cities that sit near the zero line
Reykjavik stays on UTC+0 all year. Casablanca uses UTC+1 most of the year and drops to UTC+0 only during Ramadan. Lisbon and Dublin use UTC+0 in winter and UTC+1 in summer. If a list offers a city instead of the name GMT, check the date before you trust the offset.
Common mistakes when you convert UTC to GMT
Adding or subtracting an hour out of habit
People who spend all day converting between zones tend to adjust the hour reflexively. Between UTC and GMT nothing should change. If your result differs from the input, you have mixed up GMT with London time in summer.
Treating GMT as the clock in London all year
London follows GMT from late October to late March and British Summer Time the rest of the year. A message that says “see you at 15:00 GMT” in June is ambiguous unless you know whether the writer was thinking of the clock in London.
Mixing up the sign of Etc zones
Etc/GMT+3 is three hours behind UTC, not ahead. Software that uses these names inverts the sign, and the mistake can move a schedule by six hours.
Forgetting that the date can still change in the next step
The UTC to GMT step never changes the date, but the step after it might. A job at 23:30 UTC runs at 01:30 the next day in Bucharest in winter, and at 02:30 in summer.
Frequently asked questions
Are UTC and GMT really the same?
For telling the time, yes. Their definitions differ, but the readings stay within a second of each other, so the offset is zero.
How do I convert UTC to GMT by hand?
Copy the hours and minutes unchanged and keep the same date.
Is London always on GMT?
No. London uses GMT in winter and British Summer Time, which is UTC+1, from the last Sunday in March to the last Sunday in October.
Why do web headers say GMT?
Because the standard was written when GMT was the common name for world time, and the label has been kept for compatibility.
Does anything I type leave my device?
No. The calculation runs in your browser.
More time zone conversions
Related converters include Convert UTC to CET, Convert UTC to EST, Convert CST to GMT, Convert EET to GMT, Convert GMT to EST, Convert CST to UTC, Convert CET to WET, Convert EET to EST, Convert CET to EST. The opposite direction is Convert GMT to UTC.
In short, to convert UTC to GMT you copy the clock, because the offset is zero, and you remember that the clock in London is a different thing in summer. The calculation is done locally, with no sign-up and no upload.