GMT — Greenwich Mean Time
Greenwich Mean Time — UTC+0, no daylight saving. The historical reference for the world's timezones and the current civil time of the UK in winter.
GMT in major cities right now
What is GMT?
GMT (Greenwich Mean Time) is the mean solar time at the Royal Observatory in Greenwich, London. Historically, it was the world’s time standard before being replaced for scientific purposes by UTC in 1972. It remains in common use as the civil time of the United Kingdom in winter and across several countries in West Africa year-round.
GMT has a UTC offset of +0. There is no daylight saving variant of GMT itself — when the UK observes daylight saving time in summer, the country switches to BST (British Summer Time), which is UTC+1.
Who uses GMT?
GMT is the standard time of:
- United Kingdom (in winter; switches to BST in summer)
- Ireland (under the name Irish Standard Time, equivalent to GMT in winter)
- Iceland (year-round, no DST)
- Portugal (in winter; switches to WEST in summer)
- Several West African countries including Ghana, Senegal, Côte d’Ivoire, Mali, Burkina Faso, and Liberia, where it’s used year-round with no DST
- The Canary Islands (Spain, in winter)
It is also used informally as a synonym for UTC in everyday speech, broadcasting, and aviation.
GMT vs UTC
For day-to-day purposes GMT and UTC are interchangeable — both are UTC+0. But UTC is the modern scientific standard, defined by atomic clocks and adjusted with leap seconds, while GMT is the historical mean solar time at Greenwich. Read the full comparison.