UTC vs GMT: what is the difference?
Two familiar names, one useful reference. Understand UTC, GMT, and what an offset actually means.
The useful answer for everyday conversion
UTC and GMT both correspond to a zero-hour offset in ordinary time zone conversion. If an invitation specifies 14:00 UTC or 14:00 GMT, the converter treats that as the same instant.
Their underlying definitions differ: UTC is the international time reference, while GMT refers to Greenwich Mean Time. For technical timestamps and international scheduling, UTC is generally the clearer label.
London is not always GMT
GMT is a zero offset. London is a place whose civil time changes seasonally under its time zone rules. During British Summer Time, London is one hour ahead of UTC.
If someone says “10 am London time,” select London and the appointment date. If they explicitly say “10:00 UTC,” select UTC. The converter will handle the difference.
Reading an offset
UTC+5:30 means five hours and thirty minutes ahead of UTC. At 12:00 UTC, the local time at that offset is 17:30. UTC−8 means eight hours behind UTC, so the same instant is 04:00.
The sign changes the clock reading, not the instant. Adding an offset may also move the local date forward, or subtracting one may move it to the previous day. Always include the date for cross-border plans.
Why a city is often better than an offset
An offset tells you the difference at one instant. A city time zone supplies rules that determine the correct offset for a date. Those rules can include daylight saving changes and other government decisions.
Use UTC for a universal reference. Use a named city for local appointments. Avoid treating a country as a single time zone: countries such as the United States and Australia span several zones.
Put it into practice.
Compare your cities, choose a date, and find a moment that works.
Open the time converter →Sources & further reading
Time zone rules and identifiers: IANA Time Zone Database. Time standards and clock terminology: NIST Time of Day FAQs. See how our converter calculates time for implementation details and limitations.