For everyday scheduling they show the same clock time. Technically, they are very different things.
Coordinated Universal Time (UTC) is the world’s time standard, kept by a network of atomic clocks and occasionally adjusted with leap seconds to stay aligned with Earth’s rotation. Every timezone on the planet is defined as an offset from UTC — IST is UTC+5:30, EST is UTC-5. UTC itself is not a place’s local time; it’s the reference.
Greenwich Mean Time (GMT) is the historical predecessor — mean solar time at the Royal Observatory in Greenwich, London. Today “GMT” survives mainly as a timezone name: the UK, Ireland, Iceland, and parts of West Africa use a UTC+0 timezone often labeled GMT.
The UK observes daylight saving: GMT (UTC+0) in winter, BST (UTC+1) from late March to late October. So “London time” and “GMT” differ by an hour for seven months of the year. If someone schedules “3 PM GMT” in July and actually means London local time, you could be an hour off. Check the current time in London when in doubt.
For technical work, servers, logs, and international coordination: always UTC. It never changes, has no DST, and every tool understands it. Use our UTC converter to translate UTC into any local zone.
In everyday use, yes — both show the same clock time (UTC+0). Technically UTC is the atomic time standard and GMT is a timezone. The UK only uses GMT in winter; in summer it switches to BST (UTC+1).
No. UTC never changes. That is exactly why it is used for servers, aviation, and international coordination.
No. London is on GMT (UTC+0) only from late October to late March. The rest of the year it is on British Summer Time, UTC+1.