GMT
Greenwich Mean Time
UTC+0 — No daylight saving time
Abbreviation
GMT
UTC Offset
UTC+0
Full Name
Greenwich Mean Time
DST
No
About GMT — Greenwich Mean Time
Greenwich Mean Time (GMT) is the time zone at UTC+0, historically defined by the mean solar time at the Royal Observatory in Greenwich, London. It is the time standard from which all other world time zones are offset. In winter, the United Kingdom, Ireland, and Portugal observe GMT. In summer, these countries switch to daylight saving time (BST, WEST respectively). GMT itself does not change—it remains at UTC+0 year-round. Some countries (like Ghana and Iceland) use GMT as a permanent local time without seasonal adjustments.
Countries Using GMT
- United Kingdom (winter)
- Ireland (winter)
- Portugal (winter)
- Ghana
- Iceland
Major Cities in GMT
Conversion Examples for GMT
| UTC Time | GMT (UTC+0) |
|---|---|
| 00:00 UTC | 00:00 GMT |
| 06:00 UTC | 06:00 GMT |
| 09:00 UTC | 09:00 GMT |
| 12:00 UTC | 12:00 GMT |
| 15:00 UTC | 15:00 GMT |
| 18:00 UTC | 18:00 GMT |
| 21:00 UTC | 21:00 GMT |
Related Time Zones
Tools
About GMT (GMT)
GMT (UTC+0) is a standard time zone designation used by United Kingdom (winter), Ireland (winter), Portugal (winter), and 2 other countries. Time zone abbreviations like GMT refer to a specific UTC offset rather than a geographic region — multiple time zones around the world may share the same offset while using different local names.
When scheduling internationally, it is more reliable to refer to a city name or IANA time zone identifier (like America/New_York or Asia/Dubai) than to a short abbreviation, since abbreviations are not globally standardised and can be ambiguous — for example, CST refers to both Central Standard Time (UTC−6) in North America and China Standard Time (UTC+8).
Use the conversion table on this page to see what any UTC hour maps to in GMT, and use the tools below to convert between GMT and any other time zone or city in real time.
UTC Offset vs IANA Time Zone: What's the Difference?
UTC Offset
A UTC offset like UTC+4 or UTC−5 is a simple number expressing how many hours and minutes a location is ahead of or behind Coordinated Universal Time. It is fixed and does not carry any information about DST rules or transitions.
IANA Time Zone
An IANA identifier like Europe/London or Asia/Tokyo is a database entry that includes the full history of UTC offset changes, DST rules, and historical exceptions for that location. IANA identifiers should always be preferred in software and scheduling systems.
Convert GMT Time
GMT — Frequently Asked Questions
GMT (Greenwich Mean Time) is the time at UTC+0, historically defined by the mean solar time at the Royal Observatory in Greenwich, London. It is the baseline from which all other time zones are measured.
For practical purposes of telling the time, yes—both are UTC+0. The difference is technical: UTC is maintained by atomic clocks, while GMT is based on the Earth's rotation. They are never more than 0.9 seconds apart.
The UK and Ireland use GMT in winter (switching to BST in summer). Portugal uses WET (Western European Time, also UTC+0) in winter. Iceland and Ghana use UTC+0 year-round.
Iceland uses UTC+0 permanently. Most West African countries (Ghana, Ivory Coast, Senegal, Gambia, Togo, Burkina Faso, Guinea, Sierra Leone, Liberia) observe UTC+0 without DST.