Time Zone Converter

How the conversion works

A time zone is not a fixed offset. Each one is a history of rules — when daylight saving starts and ends, when a country changed its standard time — kept in the IANA time-zone database that every major operating system and browser ships. This converter uses your browser's own copy through the Intl API and asks it for the offset at the exact instant being converted. That is why 09:00 in New York converts to 14:00 in London in January but to 13:00 in mid-March, and why nothing here needs updating when a government changes its clocks: browser updates bring the new rules.

The reverse direction is the hard part, and it is where converters quietly go wrong. Turning '14:00 in New York' into an instant means finding the offset in force at a moment you do not yet know. The converter checks the offsets on either side of any nearby clock change and keeps only the readings that genuinely come back as 14:00 in New York. Usually exactly one survives.

Daylight saving: times that never happen, and times that happen twice

When clocks spring forward, an hour of local time is skipped. In New York on 8 March 2026 the clocks go from 01:59 straight to 03:00, so 02:30 that morning never exists; in London the same happens to 01:00–01:59 on 29 March 2026. Ask for a skipped time and the converter says so and shows the moment it would have been — 02:30 becomes 03:30 — which is how calendar software handles it too.

When clocks fall back, an hour happens twice. In New York, 01:30 on 1 November 2026 occurs first in summer time (UTC−4) and again an hour later in standard time (UTC−5). The converter tells you the time is ambiguous, shows the first, and offers the second with one click. If you are scheduling anything in that hour — a server job, a night shift, a flight — say which one you mean, or use UTC. On those days the planner has 23 or 25 columns instead of 24, because that is how long the day really is.

Why the gap between two cities changes during the year

Countries that use daylight saving do not all change on the same day. The United States moves its clocks on the second Sunday of March and the first Sunday of November; the UK and the European Union on the last Sundays of March and October. So for about three weeks in March and one week around the start of November, New York is four hours behind London rather than the usual five — the classic cause of people joining a transatlantic call an hour early or late.

The southern hemisphere does it the other way round. Sydney is on summer time from early October to early April, almost exactly when London is not, so the gap between them swings between 9, 10 and 11 hours across the year. Many places — India, China, Japan, most of Africa and the Australian state of Queensland — never change their clocks, so their gap to a daylight-saving country changes twice a year even though their own time does not.

Half-hour zones and ambiguous abbreviations

Not every zone is a whole number of hours from UTC. India is UTC+5:30, Nepal UTC+5:45, Iran UTC+3:30, Afghanistan UTC+4:30, Myanmar UTC+6:30, Newfoundland UTC−3:30 (−2:30 in summer) and central Australia UTC+9:30, with Adelaide moving to +10:30 in its summer; New Zealand's Chatham Islands sit at UTC+12:45. The converter shows these offsets exactly, and the planner counts an hour that starts at 08:30 as working time, because most of it falls after 09:00.

Abbreviations are a trap. IST means India Standard Time, Irish Standard Time or Israel Standard Time; CST is Central Standard Time in North America and also China Standard Time; BST is British Summer Time and also Bangladesh Standard Time. The converter shows an abbreviation only where your browser's locale data supplies a genuine one, and always shows the numeric UTC offset beside it, because the offset is the unambiguous part. You can still search by abbreviation: typing PST, IST or AEST finds the zone most people mean.

Scheduling across time zones without mistakes

Send calendar invitations rather than times in text. An invitation stores the instant and shows each guest their own local time, which removes the arithmetic entirely. When you must write a time, write it with the city or the offset — '15:00 London time (UTC+1)' — rather than an abbreviation, and include the date, because 18:00 on a Monday in California is Tuesday morning in Asia.

Check the planner before proposing a time. Green cells are 09:00–17:00 locally, amber cells early morning or evening, grey cells night, and the line underneath names the hours when everyone is working — or the closest compromise when nobody's working day overlaps. For teams spread from the Americas to Asia there is often no shared working hour at all, and the fair answer is to rotate who takes the early or late call. For anything technical — server logs, deadlines, timestamps — use UTC, which never changes its clocks.

The converter is as current as your browser's copy of the time-zone database, which updates with the browser; an out-of-date browser can be wrong about a rule change announced at short notice, and dates before 1970 are less reliable for some regions. Your list of zones is saved in this browser for next time, and nothing is sent anywhere.