GMT (Greenwich Mean Time) is the mean solar time at the Greenwich meridian in London. The clock above shows the current GMT time, which matches UTC. Brasília is on GMT-3, that is, 3 hours behind.
Who is on GMT right now?
| Place | Time now | Offset now | On GMT now? |
|---|---|---|---|
| Reykjavik (Iceland) | 23:27:31 | UTC+0 | Yes |
| Accra (Ghana) | 23:27:31 | UTC+0 | Yes |
| Dakar (Senegal) | 23:27:31 | UTC+0 | Yes |
| London (United Kingdom) | 00:27:31 | UTC+1 | No |
| Dublin (Ireland) | 00:27:31 | UTC+1 | No |
| Lisbon (Portugal) | 00:27:31 | UTC+1 | No |
| Brasília (Brazil) | 20:27:31 | UTC-3 | No |
What GMT is
Greenwich Mean Time was defined in 1884 as the mean solar time at the Royal Observatory in Greenwich, east London, where the prime meridian (0° longitude) passes. For a century it was the world's reference clock, which is why airlines, weather services and the shipping world still say "GMT". Since 1972 the official reference is UTC, kept by atomic clocks, but GMT remains a legal time in the United Kingdom and a common label for the zone at offset zero.
GMT vs UTC
In everyday use, GMT and UTC show the same clock reading. The difference is technical: GMT follows the Earth's rotation (so it drifts slightly), while UTC is atomic time adjusted by leap seconds to stay within 0.9 seconds of the Earth's rotation. If you are scheduling a meeting or reading a timestamp, treat them as identical; for software, prefer UTC. Our UTC time page covers the standard in more detail.
The British summer-time nuance
Here is the trap: the United Kingdom is not on GMT all year. From the last Sunday of March to the last Sunday of October it uses British Summer Time (BST), which is UTC+1. In 2026 that period runs from Sunday, March 29, 2026 to Sunday, October 25, 2026, with the change at 01:00 UTC. So "London time" equals GMT only in winter. Ireland and Portugal do the same (their summer times are IST and WEST). Meanwhile Iceland, Ghana, Senegal and a handful of other countries stay on GMT permanently. That is why a London meeting that is 3 hours ahead of Brasília in winter is 4 hours ahead in summer.
What GMT-3 means
The suffix says how far a zone is from Greenwich. GMT-3 is 3 hours behind, which is Brasília's zone (UTC-3). To convert GMT to Brasília time, subtract 3 hours; to convert Brasília to GMT, add 3. Examples: 09:00 GMT = 06:00 in Brasília; 14:00 in Brasília = 17:00 GMT; 01:00 GMT = 22:00 the previous day in Brasília. Because Brazil has no daylight saving time, this never changes.
| GMT | Brasília |
|---|---|
| 00:00 | 21:00 (previous day) |
| 03:00 | 00:00 |
| 06:00 | 03:00 |
| 09:00 | 06:00 |
| 12:00 | 09:00 |
| 15:00 | 12:00 |
| 18:00 | 15:00 |
| 21:00 | 18:00 |
To convert between any two cities, use the time zone converter; for the full picture of offsets read the time zones guide, and for clock changes see daylight saving time.