UTC vs GMT: What Is the Difference?
UTC and GMT show the same time, but one is a standard and the other is a time zone. Here is the difference.
The short answer
For everyday use, UTC and GMT show the same time. The difference is what they are: UTC (Coordinated Universal Time) is the world's time standard, kept by atomic clocks. GMT (Greenwich Mean Time) is a time zone, used by the UK, Ireland, Portugal and parts of West Africa in winter.
Where GMT came from
GMT is the mean solar time at the Royal Observatory in Greenwich, London. Railways and shipping made it the world's reference in the 19th century, and in 1884 the Greenwich meridian became longitude 0.
Why UTC replaced it
The Earth's spin is slightly irregular, so a time based on the sun drifts. Since 1972, UTC has been kept by atomic clocks and adjusted with occasional leap seconds to stay within 0.9 seconds of solar time. Scientists, pilots, computers and the internet all use UTC.
GMT in summer
The UK switches to British Summer Time (BST, UTC+01:00) from late March to late October. So in summer, London is not on GMT, but UTC does not change. This is the most common mix-up: "GMT" in a summer meeting invite can be one hour off from London time.
| UTC | GMT | |
|---|---|---|
| What it is | Time standard | Time zone |
| Kept by | Atomic clocks | Defined as UTC+00:00 |
| Changes in summer | Never | UK moves to BST |
| Used by | Science, aviation, computers | UK and others in winter |
See the current UTC time.
Questions
Is UTC the same as GMT?
They show the same clock time, but UTC is a standard and GMT is a time zone. Use UTC when precision matters.
Does UTC change for daylight saving?
No. UTC never changes. Time zones move relative to it.
What does the Z in 14:30Z mean?
Z stands for Zulu time, which is UTC. 14:30Z is 14:30 UTC.
By the TimeNowTools team · Last reviewed 20 October 2026