GMT to UTC converter
Convert GMT to UTC. They are the same time in winter; in summer the UK moves to BST, so London is one hour ahead of UTC.
UTC and London show the same time (GMT vs UTC).
When the GMT versus UTC question matters
GMT and UTC are so close that most people treat them as the same clock, and for conversion purposes they are. 12:00 GMT is 12:00 UTC. The difference is one of definition: GMT is the time zone of the Royal Observatory at Greenwich and the UK’s winter clock, whereas UTC is the atomic-time standard that civil clocks are measured against.
The practical catch is the word "London". If you mean the actual time on a London wall clock, it equals UTC from late October to late March and is UTC plus one hour from late March to late October, when the UK is on British Summer Time. This page treats GMT as the UK clock, so it shows both situations.
For most readers the answer is "no difference", but there are a few cases where precision matters.
UK schedules written in GMT
Broadcasters, universities and councils often write "GMT" for UK time all year.
- A "9 AM GMT" meeting in January is 09:00 UTC
- A "9 AM GMT" meeting in July is usually 08:00 UTC (9 AM BST)
- Check the invite: a literal GMT time in July is 10:00 BST
If the date falls in summer, ask whether the sender means London time or true GMT.
Software and data
Most programming languages treat "GMT" and "UTC" as the same offset, and some libraries use one name for the other.
- A timestamp ending in Z or "UTC" is zero offset
- An HTTP header such as Date uses GMT as the label
- An Etc/GMT zone is simply UTC with a different name
HTTP dates in GMT are always equal to UTC, whatever the season in London.
Aviation and shipping
Pilots and mariners use "Zulu" time, which is UTC, and older charts sometimes say GMT.
- A 1430Z forecast is 14:30 UTC and 14:30 GMT
- A flight plan in UTC does not change in summer
- A London departure at 1430 local in July is 13:30 UTC
In summer the London departure time and the Zulu time differ by an hour.
Deadlines in GMT
A competition deadline written as noon GMT means 12:00 UTC. In summer, a UK-based organiser may still say GMT while thinking in London time, so a call that says "noon GMT, 1 July" could mean 12:00 UTC or 11:00 UTC. The safe approach is to write the UTC time.
For exam boards, ticket releases and flights from London, the local time governs. A ticket release at 10:00 AM London time is 09:00 UTC in summer and 10:00 UTC in winter. Use the converter on this page for the exact date.
Zero hours in winter, one hour in summer
The UK changes its clocks at 1:00 AM UTC on the last Sunday of March and again on the last Sunday of October. Between those dates London is on BST, UTC+1. GMT and UTC differ by one hour on the London wall clock for roughly 7 months of the year.
- Mar 28, 2027: London moves to BST (UTC+1); the gap becomes 1 hour
- Oct 31, 2027: London moves to GMT (UTC+0); the gap becomes zero
UTC itself never changes. If you hold a meeting at a fixed UTC time, the UK participants will see it move by an hour in March and October. If you hold it at a fixed London time, everyone outside the UK sees the UTC time move instead.
London to UTC, every hour
Times are for Nov 6, 2026, when UTC and London show the same time. The gap changes on the dates listed above. Green rows are the hours when both places are inside a 9-to-5 day.
| London (GMT) | UTCUTC, 0 hrs |
|---|---|
| 12:00 AM (midnight) | 12:00 AM |
| 1:00 AM | 1:00 AM |
| 2:00 AM | 2:00 AM |
| 3:00 AM | 3:00 AM |
| 4:00 AM | 4:00 AM |
| 5:00 AM | 5:00 AM |
| 6:00 AM | 6:00 AM |
| 7:00 AM | 7:00 AM |
| 8:00 AM | 8:00 AM |
| 9:00 AM | 9:00 AM |
| 10:00 AM | 10:00 AM |
| 11:00 AM | 11:00 AM |
| 12:00 PM (noon) | 12:00 PM |
| 1:00 PM | 1:00 PM |
| 2:00 PM | 2:00 PM |
| 3:00 PM | 3:00 PM |
| 4:00 PM | 4:00 PM |
| 5:00 PM | 5:00 PM |
| 6:00 PM | 6:00 PM |
| 7:00 PM | 7:00 PM |
| 8:00 PM | 8:00 PM |
| 9:00 PM | 9:00 PM |
| 10:00 PM | 10:00 PM |
| 11:00 PM | 11:00 PM |
“next day” and “previous day” mean UTC is on a different calendar date from London.
Quick answers
Is GMT the same as UTC?
For conversion, yes: 12:00 GMT equals 12:00 UTC. GMT is a time zone and UTC is the atomic time standard.
Is London on GMT all year?
No. London uses GMT in winter and BST (GMT plus one hour) in summer.
What is 3 PM GMT in UTC?
15:00 UTC.
Why does the converter show a one hour gap in summer?
Because London is on BST in summer, one hour ahead of UTC. The label "GMT" is used here for UK time.
Which should I use in an invite, GMT or UTC?
Use UTC for a fixed global time, or write "London time" if you mean the local clock.