UTC to GMT
the prime meridian to London.
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All date & timeQuestions
What time is GMT when it is 12:00 UTC?
12:00. Greenwich Mean Time is no difference the same time as Coordinated Universal Time in January and 1 hour ahead of it in July. The gap moves because London observes daylight saving and the prime meridian does not, so the difference between them is not a fixed number. A 9-to-5 day in the prime meridian overlaps a 9-to-5 day in London for 8 hours, between 09:00 and 17:00 UTC.
Is the difference between UTC and GMT the same all year?
No, and this is the pair where that matters. Greenwich Mean Time is no difference the same time as Coordinated Universal Time in January and 1 hour ahead of it in July. The gap moves because London observes daylight saving and the prime meridian does not, so the difference between them is not a fixed number. Booking a recurring call across these two and assuming one number will drift by an hour twice a year — check the date, not just the zones.
What do UTC and GMT actually stand for?
UTC is Coordinated Universal Time, the zone covering the prime meridian, currently UTC+0 in January. GMT is Greenwich Mean Time, covering London, at UTC+0. UTC never changes for daylight saving, which is why servers, aviation and broadcasting all run on it. It is the reference every other zone is defined against, including GMT — the two are the same clock time, but GMT is a time zone and UTC is a time standard.
Anything worth knowing about Greenwich Mean Time?
GMT and UK time are the same thing only in winter. From late March to late October London runs on British Summer Time, an hour ahead of GMT, so a meeting booked as 'GMT' with someone in London is an hour out for most of the year.
When is a good time to call between the prime meridian and London?
A 9-to-5 day in the prime meridian overlaps a 9-to-5 day in London for 8 hours, between 09:00 and 17:00 UTC. If the call has to happen outside that, the fairer arrangement is usually to alternate which side takes the awkward hour rather than always asking the same one.
How it works, and more about utc → gmt
The difference, and whether you can rely on it
Coordinated Universal Time and Greenwich Mean Time read the same clock in January. In July it is 1 hour ahead instead. That is the part worth carrying away: this is not a pair you can memorise a single number for.
Why the gap moves
London observes daylight saving; the prime meridian does not. So the clocks in one city move twice a year while the other stays put, and the distance between them changes with them. Any calculation you did in one season is wrong in the other. The converter above uses the date you give it rather than today’s offset, which is the only way to get a future meeting right when it falls on the other side of a changeover.
When you can both be at a desk
A standard working day in the prime meridian overlaps one in London between 09:00 and 17:00 UTC — 8 hours. Anything outside that asks somebody to start early or finish late.
Reading the abbreviations literally will mislead you
UTC strictly means one fixed offset, but almost nobody uses it that way. People write it to mean the time in the prime meridian, which shifts if the city observes daylight saving, which this one does not. This page follows the common usage rather than the strict one, because the strict reading gives an answer that is wrong for a good part of the year.
UTC never changes for daylight saving, which is why servers, aviation and broadcasting all run on it. It is the reference every other zone is defined against, including GMT — the two are the same clock time, but GMT is a time zone and UTC is a time standard. GMT and UK time are the same thing only in winter. From late March to late October London runs on British Summer Time, an hour ahead of GMT, so a meeting booked as 'GMT' with someone in London is an hour out for most of the year.
Scheduling something recurring
For a one-off, the converter above is the whole job. For a standing meeting across these two zones, where the gap changes, it is worth putting the invitation in a calendar that stores the zone rather than the time — then the changeover is handled for you and nobody has to remember. If you are trying to find a slot across more than two places at once, the meeting planner shows a whole day at a glance instead.