How far a place's clock is from UTC at a given moment — which is not a constant.
A UTC offset is the difference between a place's civil time and Coordinated Universal Time, written as +05:30 or −08:00. It is the number you actually need to convert a time, and it is a property of a moment rather than of a place.
The same place has different offsets at different times of year wherever daylight saving applies. Storing an offset instead of a zone freezes a conversion that was only true when it was made, which is why systems that record '+01:00' rather than 'Europe/London' start producing wrong answers at the end of March.
Offsets are also not all whole hours, which surprises people writing conversion code for the first time.
One instant, four clocks. Each is the same moment written in a different place's civil time — and two of them are not on a whole hour.
| 🇬🇧 | 09:00, Monday 15 March 2027United Kingdom | UTC+00:00Still on standard time — the UK does not move its clocks until 28 March that year. |
| 🇮🇳 | 14:30, Monday 15 March 2027India | UTC+05:30The same instant. India keeps one zone across the whole country, on a half-hour offset. |
| 🇳🇵 | 14:45, Monday 15 March 2027Nepal | UTC+05:45Fifteen minutes ahead of India, and the reason a quarter-hour field is not optional. |
The zone is the region and its rules. The offset is what those rules produce at one instant, and it changes.
Standard time is a place's offset outside any summer-time period. The current offset may be that or an hour more.
See also time zone · standard time · half hour offset · daylight saving time
We hold this as derived from the presentation zone at the date being asked about. See what we hold.