How the conversion works
Every time zone is defined by its offset from UTC, the world's reference time. Converting between two zones is just arithmetic with those offsets:
The hard part is knowing what the offsets actually are on a given date, because most zones change them twice a year for daylight saving, on dates that differ from country to country. This converter reads the offsets from your browser's built-in copy of the IANA time zone database, the same rule set operating systems and servers use, so the daylight saving switch is applied for the exact date you pick. Everything runs in your browser and nothing is uploaded.
Worked examples
Daylight saving moves the goalposts
The gap between two zones is not fixed. London and New York are 5 hours apart for most of the year, but the US puts its clocks forward on the second Sunday in March while the UK waits until the last Sunday, so for a couple of weeks each spring the gap shrinks to 4 hours. That fortnight is a classic source of missed calls, because a meeting booked as "3pm London, 10am New York" silently stops lining up. The southern hemisphere flips the other way: Sydney is 11 hours ahead of London around Christmas but only 9 ahead in June, because the two cities do daylight saving in opposite halves of the year.
The clock changes themselves create odd moments. When clocks go forward an hour of wall time simply never happens, and when they go back an hour happens twice. If you enter a time inside a spring-forward gap, the tool tells you and converts the time the clocks actually showed. For scheduling across zones, the safest habit is to agree the time in one named zone (or in UTC) and let each person convert, which is exactly what this page is for.
Half hours and other quirks
Offsets are decisions made by governments, so they are not all neat whole hours. India runs the whole country on UTC+05:30, Nepal goes one better at UTC+05:45, and South Australia uses a half-hour offset too. Some places skip daylight saving entirely (Japan, India, most of Australia's north), which is why the zone list here names cities rather than countries: the rules genuinely differ region by region, and the IANA database tracks each one separately.
UTC itself never changes and makes a handy neutral reference, which is why aviation, shipping and computing all log time in it. If you work with Unix timestamps, which count seconds since 1 January 1970 UTC, our Unix timestamp converter translates those into readable dates, and the countdown tool can tick down to a deadline once you have converted it into your own local time.
Frequently asked questions
Does the converter handle daylight saving time?
Yes. It uses your browser's built-in time zone database to find the UTC offset actually in force in each zone on the date you enter, so a London to New York conversion gives a 5 hour gap for most of the year and correctly drops to 4 hours for the couple of weeks in spring when the US has changed its clocks but the UK has not.
What is the difference between UTC and GMT?
For everyday purposes they are the same time. UTC (Coordinated Universal Time) is the modern standard kept by atomic clocks, while GMT is the historical name and survives as the UK's winter time zone. In summer the UK is on BST, one hour ahead of UTC, so London time is only sometimes the same as UTC.
Why are some zones offset by half an hour?
Offsets are political choices, not laws of nature. India uses UTC+05:30 as a single compromise zone for the whole country, Nepal uses UTC+05:45, and parts of Australia use half-hour offsets too. That is why the converter works in minutes rather than whole hours.
What happens if I enter a time that does not exist?
When clocks go forward, one hour vanishes: in London the small hours of the last Sunday in March jump from 01:00 straight to 02:00. If you enter a time inside that gap the tool warns you and converts the time the clocks actually showed instead.
Is anything sent to a server?
No. The conversion runs entirely in your browser using its built-in copy of the IANA time zone database, which is the same data operating systems use. Keeping your browser up to date keeps the daylight saving rules current.