Time Zone Converter

A time zone converter takes a moment described in one place and tells you how it is described in another. Not a different moment — the same moment, read on a different clock. When it is 9:00 PM in Mumbai it is 11:30 AM in New York, and those are one instant with two names.

Different places keep different clocks because the sun does not rise everywhere at once, and because a country would rather have noon near the middle of its day than match a neighbour. The lines between zones are political rather than geometric: China spans five geographic hours and uses one clock; India uses a half-hour offset so a single time works reasonably from Gujarat to Assam.

What makes conversion harder than subtraction is that the gap between two places is not constant. Around a third of the world moves its clocks twice a year, on dates that do not agree, so the difference between London and New York is five hours for most of the year and four for about a fortnight each spring. Everything in this tool is calculated for the date you choose, from the same time zone database your operating system uses.

Local time

What a clock on the wall says. It is meaningless on its own — “3 PM” is not a moment until you know where the wall is.

UTC

The reference every clock is defined against. An instant has exactly one UTC value, which is what makes UTC the right thing to store, log and agree on.

UTC offset

How far a local clock sits from UTC — +05:30, −04:00. Local time is UTC plus the offset, and conversion is just applying one offset and removing another.

Time zone rules

A zone is not an offset, it is a history and future of offsets. The IANA database records, for every zone, which offset applied when — including the changes each government has announced. That is why a converter should ask for a city rather than a number.

Date changes

Offsets span 26 hours from UTC−12 to UTC+14, so the same instant routinely falls on two different calendar dates. This is the single most common way a meeting is missed — by exactly 24 hours.

1India        12 August, 12:30 AM2New York     11 August, 3:00 PM

Daylight saving time

Twice a year many zones change their offset. That means an hour is skipped in spring and repeated in autumn, and it means any difference you memorised is wrong for part of the year.

Coordinated Universal Timeis the standard the world’s clocks are coordinated against. It is kept by a weighted average of around 400 atomic clocks in some 80 institutions, and it is nudged with the occasional leap second so it stays within a second of the time the Earth’s rotation implies.

Three things make it useful. It is not a place, so nobody owns it. It never observes daylight saving, so it never jumps. And every other zone is defined as an offset from it, so it is the one clock all the others agree about.

In practice that makes UTC the right thing to store and to log. A server that records local time has thrown information away — twice a year it will write the same hour twice and have no way to say which was which. A server that records UTC can always produce local time later, for any zone, correctly. Logs usually store that instant as a Unix timestamp, which the Unix timestamp converter turns back into a readable date in the zone you pick.

The odd initialism is a compromise: English wanted CUT, French wanted TUC, and UTC belongs to neither language.

An offset is how far a local clock runs from UTC, written with a sign, hours and minutes. Positive is east of Greenwich — ahead, seeing the sun sooner. Negative is west — behind.

1UTC+05:30   India — five and a half hours ahead2UTC+01:00   Central Europe in winter — one hour ahead3UTC+00:00   UTC itself, and the UK in winter4UTC-04:00   New York in summer — four hours behind5UTC-07:00   California in summer — seven hours behind

Offsets are not all whole hours, and code that assumes they are breaks in real places. India is +05:30. Nepal is +05:45. Newfoundland is −03:30. Chatham Islands sit at +12:45. The full range runs from −12:00 to +14:00 — twenty-six hours, which is why there are always two calendar dates in progress somewhere on Earth.

A zone has more than one offset. New York is −05:00 in winter and −04:00 in summer; both are New York. Quoting one without a date is quoting half the answer.

What it is

Moving the clock forward an hour for part of the year so that evening daylight lasts later. In spring the clocks jump forward and an hour disappears; in autumn they go back and an hour happens twice.

Why some countries use it

The original argument was energy: less lighting in the evening. The evidence for that has weakened as lighting became efficient and air conditioning did not, and the modern arguments are mostly about leisure and retail. Support is far from universal — the EU voted to abolish it in 2019 and has not implemented that, and most of Asia and Africa never adopted it at all.

Why UTC offsets change

Because the offset isthe clock’s relationship to UTC, and moving the clock moves that relationship. New York does not stop being Eastern Time in summer; Eastern Time changes from −05:00 to −04:00.

Why time differences change during the year

Because the two ends shift on different dates, or one shifts and the other does not:

• London and New York. Both observe it, on dates two weeks apart. Five hours becomes four for that fortnight each spring.
• India and New York. Only New York shifts, so the gap swings between 9:30 and 10:30 twice a year.
• London and Sydney. Both shift, in opposite seasons. The gap moves between 9, 10 and 11 hours across a year.

This tool never stores a difference. It reads both offsets for the date you chose and subtracts them, which is the only method that is right in December as well as in July.

1. 1. Pick the source zone.Search by city — “Mumbai”, “London”, “PST” all work. You do not need to know the IANA identifier, though it is shown so you can confirm the right one.
2. 2. Set the date and time.Or leave “use current time” on and the page tracks the clock live. The date matters: it decides which offset applies.
3. 3. Pick the destination. The converted time appears immediately, with the date beside it.
4. 4. Check the date badge.If the conversion crossed midnight, the result is marked “next day” or “previous day”. This is the part worth reading twice.
5. 5. Add the rest of the room. Any number of further zones up to twelve, all showing the same instant.
6. 6. Copy it. The copy button produces the whole list as text, ready to paste into an invitation or a message.

The difference between two zones is the difference between their offsets at a particular instant. The tool reads both from the IANA database for the date you selected and subtracts them — it never uses a remembered number.

112 March 2026    London is 4 hours ahead of New York212 July 2026     London is 5 hours ahead of New York3 4Both are correct. The US moved its clocks on 8 March5and the UK moved on 29 March, so for three weeks the6usual five-hour gap is four.

Half-hour and quarter-hour offsets are handled throughout, so India shows as 9 hours 30 minutes ahead of New York rather than being rounded to a number that would make you half an hour late.

This is a gap between two clocks, not between two dates. For the span between one calendar date and another — counted in years, months and days rather than hours — the age calculator has a date difference mode that never touches time zones at all.

Add up to twelve zones and the comparison shows all of them at the same instant — local time, weekday, date, UTC offset, abbreviation and daylight saving status. It is the view for the question “who is awake right now?”

1India          9:00 PM    UTC+05:302Singapore     11:30 PM    UTC+08:003Tokyo         12:30 AM    UTC+09:00   next day4Sydney         1:30 AM    UTC+10:00   next day5London         4:30 PM    UTC+01:006New York      11:30 AM    UTC-04:007Los Angeles    8:30 AM    UTC-07:00

Reorder the list so the people you work with most are at the top, star the zones you use often so they lead the search, and use the timeline view to see the whole day at once rather than a single moment.

The planner steps through the day in half-hour slots. For each one it works out the local time in every zone and checks it against that zone’s working hours, then reports the windows where they overlap.

Every window is graded, and the grades mean something specific:

• Excellent — everybody is inside their working hours.
• Good — everybody is working or within an hour of it. Somebody starts early or stays a little late.
• Acceptable — at least half the room is available and nobody has been asked to wake in the night.
• Outside working hours — no usable overlap.

Each zone can have its own hours, and a range that ends before it starts — 22:00 to 06:00 — is read as a night shift rather than as no hours at all.

Some pairs have no answer. India and California share no working day at any setting, and the tool says so rather than proposing something at 3am and calling it a compromise. When that happens the real options are a rotating early-or-late call, or async — and knowing which pairs are in that category is itself useful.

The pairs people look up most. Note that almost none of them has a single answer: where either side observes daylight saving, the difference depends on the date. Set the date in the converter and it works out which applies.

Common abbreviations, and what they actually mean:

• UTC — Coordinated Universal Time, the reference. No offset, no daylight saving.
• GMT — Greenwich Mean Time. The same clock as UTC in practice; still used in the UK and in a few zone names.
• IST — India Standard Time, +05:30. Also Irish Standard Time and Israel Standard Time.
• EST / EDT — US Eastern, −05:00 in winter and −04:00 in summer.
• CST / CDT — US Central, −06:00 and −05:00. CST is also China Standard Time at +08:00 and Cuba Standard Time.
• MST / MDT — US Mountain, −07:00 and −06:00. Arizona stays on MST all year.
• PST / PDT — US Pacific, −08:00 and −07:00.
• BST — British Summer Time, +01:00. Also Bangladesh Standard Time at +06:00.
• JST — Japan Standard Time, +09:00. No daylight saving since 1951.
• AEST / AEDT — Australian Eastern, +10:00 and +11:00. Queensland does not shift; New South Wales does.

Abbreviations are ambiguous and are not a standard. CST is three different offsets. IST is three different countries. BST is two. There is no registry, and different software resolves them differently — which is exactly how a meeting ends up scheduled twelve hours out.

When accuracy matters, use the IANA identifier: America/New_York rather than EST, Asia/Kolkatarather than IST. It names a place, it carries that place’s full history of rules, and it cannot be confused with anywhere else. Abbreviations are for conversation; identifiers are for anything written down.

Meetings

Send every invitation with the time in each participant’s zone written out, and let the calendar handle the conversion rather than doing it in your head. Name the city, not the abbreviation.

Standups

A daily synchronous standup across more than about six hours of spread will always be someone’s early morning or late evening. Rotate it, or write it down instead — the timeline view makes the size of the problem obvious.

Customer support

Follow-the-sun coverage is a time zone problem before it is a staffing one. Put each shift on the timeline and the uncovered hours show up as gaps.

Collaboration

Overlap is a budget. Two hours a day is enough for a standup and one conversation, and not enough for pairing. Knowing the number changes how you plan the work.

Project planning

A deadline of “Friday” is 24 hours wide across a global team. Say “Friday 17:00 UTC” and it is a moment. Remember that recurring meetings drift when one side changes clocks and the other does not — a weekly call can move by an hour twice a year with nobody editing anything.

• Always specify the date. A difference without a date is a guess that is wrong for part of the year.
• Consider daylight saving on both sides. Two zones, two sets of rules, two different change dates. The weeks between them are where mistakes live.
• Prefer city-based zones. America/New_York is unambiguous and carries its own rules; UTC−5 is a number that stops being true in March.
• Avoid abbreviations in writing. CST is three offsets and IST is three countries. Use them in conversation, not in an invitation.
• Check the calendar date, not just the clock. Being 24 hours out is far more common than being an hour out, and much more embarrassing.
• Consider working hours, not just overlap. A time that is technically available at 7am for one side and 9pm for the other is not a good meeting, and it will be quietly resented.
• Store UTC, display local. For anything a program has to remember, this single rule prevents most time zone bugs.