Time Zone Converter

What a time zone converter actually computes

Every zone is an offset from Coordinated Universal Time. New York is UTC-5 in winter and UTC-4 in summer; India is UTC+5:30 all year. Converting between two places is arithmetic on those offsets, and the arithmetic is the easy part. What goes wrong is knowing which offset applies on the date you care about. An offset is not a property of a place, it is a property of a place at a moment: around half the world moves its clocks twice a year, the switch dates differ by country, and governments change the rules.

The naive method fails in a repeatable way. You look up “New York is five hours behind London”, book a call three weeks out, and on that date the United States has already moved its clocks while the United Kingdom has not. That week the gap is four hours, and one of you joins an hour late. Time zone math done from memory is a bet that no country shifted between today and the meeting.

So this page asks for a date as well as a time. Each city is formatted with Intl.DateTimeFormat, the browser API that reads your device’s copy of the IANA time zone database, which means the offset on each card is the one that will be in force on the day you picked. Times use a 24-hour clock.

Which cities and zones to add

• A recurring team call: one city per person, not one per country. The United States, Canada, Australia, Brazil, Mexico, Indonesia and Russia all span several zones, so “the US team” is not a time.
• A team spread over more than two zones: add UTC as well. It never shifts, so it is the one line you can quote in a document and still be right six months later.
• Anything that arrives as an abbreviation: add the city instead. CST on its own could be Chicago, Shanghai or Havana.
• Places that look identical but are not: Phoenix stays on standard time all year while Denver shifts, so for half the year they are an hour apart even though both are called Mountain. Brisbane and Sydney are the same trap.
• Half-hour and quarter-hour zones: India (UTC+5:30) and Nepal (UTC+5:45) are rounded to the wrong hour more than any others. Iran, Afghanistan, Myanmar, Newfoundland and the Chatham Islands are in the same family.
• A stable anchor: Tokyo, Taipei, Singapore, Hong Kong, Honolulu and Brisbane never change their offset, which makes them useful reference points when everything else is moving.

How to find a slot for New York, London and Tokyo

1. Use Add city to put New York, London and Tokyo in the list, and drop anything you do not need with the cross on the card.
2. Pick the real date of the meeting, not today. This is the step that protects you from a clock change you did not know about.
3. Move the hour until no city sits in the middle of its night. For these three the band is narrow: early morning in New York is early afternoon in London and evening in Tokyo. Around 08:00 in New York it is about 13:00 in London and 21:00 or 22:00 in Tokyo, depending on the season. An hour later and Tokyo is near bedtime; an hour earlier and New York is getting up in the dark.
4. Read the date on each card, not only the clock. A meeting that is Tuesday evening in New York is Wednesday morning in Tokyo, and the invitation has to say which day.
5. Write the slot down with a zone attached to every figure: “Tue 08:00 New York / 13:00 London / 21:00 Tokyo”.

How to convert a flight or a webinar time

Airlines, conference organizers and streaming schedules publish local time at the venue and offer no conversion. Add the venue city and your own, set the date and time to the published figure, and read your own card.

1. Flights: departure and arrival times on a ticket are each local to their own airport. Add both cities and enter the departure time to see what the arrival clock will say. The gap between the two readings is not the length of the flight: a trip west can land close to the hour it took off, and a trip east can cost you most of a day.
2. Webinars and launches: enter the advertised time in the advertised city. If the listing gives only an abbreviation such as PT or CET, find out which city the organizer is in first.
3. Deadlines: a submission that closes at 23:59 closes at 23:59 in somebody’s zone. Convert it, then set your reminder an hour earlier than the converted figure.

Sharing the converted times

• Copy it as text: select the time on a card and copy it the usual way, Ctrl+C on Windows, Cmd+C on a Mac, or press and hold then tap Copy on a phone. Take the city name with it. A bare time in a chat message is the mistake this tool exists to prevent.
• Put it in a calendar invitation: the most reliable option, because Google Calendar, Outlook and Apple Calendar store an event with a zone and every guest sees it converted on their own device. Create it in the zone you agreed on, then check the event’s zone before sending.
• Write it in a document or a ticket: ISO 8601 with an explicit offset, such as 2026-06-22T10:00+08:00, is unambiguous, sorts correctly and can be read by software.
• Put it in the subject line: “Sync, Tue 08:00 New York / 13:00 London” survives being forwarded, which a time buried in a calendar description does not.

Where the answer differs: calendars, invites and apps

• Google Calendar and Outlook: an event carries a time zone, so guests abroad see their own local time without doing anything. Both can show a second zone beside the first in the calendar view, and both let you set the zone on an individual event, which is what you want when booking something in a city you are not in.
• Recurring meetings: a repeating series is anchored to the zone it was created in. When that country changes its clocks and the other participant’s country has not yet, the series moves by an hour for everyone except the organizer. That is expected behavior rather than a bug, and it is why a standing call is worth re-checking in March, April, October and November.
• Apple Calendar: time zone support is a setting. With it off, events can behave as though they belong to whatever zone the device is in, which is confusing while you travel. Turning it on lets you pin an event to a named city.
• Browsers: this page, like every website, takes its idea of “your” zone from the operating system, and a VPN does not change it. If the local card looks wrong, the device clock or its zone setting is wrong, and every other site will agree with the device rather than with you.
• Apps that show abbreviations: chat tools, meeting apps and event listings print EST, PT or CET next to a time. Treat that as a hint about where the organizer is, then confirm it against a city.
• Devices that are out of date: the time zone database is revised several times a year as countries change their rules, and it reaches you through system updates. A phone, laptop or server left un-updated can be an hour out for a country that changed recently.

Things to watch out for

Your device clock is the starting point. If its zone is wrong, every card is wrong by the same amount, so check that setting first whenever a result surprises you.

Two hours a year do not behave. On the spring forward date one local hour never happens, and on the fall back date one local hour happens twice. A meeting booked inside either window is genuinely ambiguous, so pick a different hour instead of arguing afterwards about which one was meant.

Rules change, sometimes at short notice. Countries have abolished, restored and moved their daylight saving rules in recent years, and ending seasonal clock changes has been debated in both the United States and the European Union. Everything here about switch dates describes what is usual, so check the current year before planning far ahead, and treat dates from before a rule change with extra care.

Reading the output. Times use a 24-hour clock, so 14:30 is half past two in the afternoon. Dates spell the month out because 09/12 means 12 September in some countries and 9 December in others, and a converter is the wrong place to add a second ambiguity.