data tool
Time zone converter
Enter a date, a time and the zone it is in, and read the same moment in every zone on your list, with a mark wherever the date is a day ahead or behind. Offsets come from your browser's own time zone database for that exact date, so daylight saving is applied the way it will be on the day.
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- Runs on your device, nothing is uploaded
- Free, no sign in
- No watermark, no file limit
How it works
- 1
Set the date and time
Pick them in Date and Time, or press Now. Start from UTC switches the starting zone to UTC and keeps your old one on the list.
- 2
Say which zone it is in
In this time zone starts as your own zone. Type a city or an IANA name and choose from the suggestions.
- 3
Build the list
Type a zone in Add a time zone and press Add or Enter. Each row has a remove button, so the list can be cut down to the people who matter.
- 4
Read and copy
Each row shows the time, the date, the abbreviation and the UTC offset, with Next day or Previous day where the date has changed. Copy all times gives one line per zone.
Why the date matters as much as the time
An offset is not fixed for a zone; it depends on the day. Sydney is UTC+10 in July and UTC+11 in January, London moves between UTC and UTC+1, and the two switch on different weekends in opposite directions. So a converter that applies today's offset to a date next month can be an hour out, and for a few weeks each spring and autumn it can be two. This tool asks the browser for the offset in force at the exact instant you entered, in every zone separately, which is the only way to get a date in March or October right.
The day boundary
The most expensive mistake in cross zone scheduling is the date, not the hour. In January, a 9:00 call on Monday in Melbourne is 17:00 on Sunday in New York and 22:00 on Sunday in London. Every row that lands on a different calendar date from the starting zone carries a mark: Next day in blue, Previous day in amber, and a day count for the rare jump of two. When you send a time to people in several zones, copy the lines out with their dates, rather than the time alone.
Deadlines and expiry across zones
A deadline written as a date alone, such as sign by 14 March, means a different moment in each zone. Systems avoid that by storing an instant. An e-sign envelope, for example, expires 30 days after it is created, counted from that moment, so a signer far ahead or behind the sender sees the cut off at a different local hour and sometimes on a different local date. When a deadline matters, give the time and the zone, or convert it here and send each person their own local time.
Zone names and abbreviations
IANA names such as America/New_York follow the city whose clocks a whole region keeps, and they carry the full history of that region's offsets. Abbreviations such as EST, IST or CST are shorter but ambiguous: IST is used for India, Ireland and Israel, and CST for both central North America and China. The tool shows the abbreviation the browser gives for that date beside the numeric offset, and the numeric offset is the one to trust.
Limits worth knowing
Every offset comes from the time zone database built into your browser, which is updated with the browser itself. When a government changes its rules at short notice, which happens several times a year somewhere, an out of date browser can be an hour wrong for that place until it updates. Nothing is uploaded and nothing is stored, ever, including the list of zones you build.
Limits
- Uses the browser's IANA time zone database, so a rule change, such as a country dropping daylight saving, lands when the browser updates.
- A time skipped when clocks go forward is moved to the next valid time, and a time that happens twice when clocks go back shows the first of the two. Both are flagged.
- The list of zones is not saved; a refresh brings back the starting list.
What it does not do
- It does not find a meeting slot that suits everyone; it converts the time you give it.
- It does not read calendar invitations or add events to a calendar.
- It does not convert historic dates reliably before about 1970, where the zone database is less complete.
Questions people ask
What is the difference between GMT and UTC?
For converting times, none. UTC is the atomic time standard that civil time is based on, and GMT is the old name for the mean solar time at Greenwich, now used as the winter time zone of the United Kingdom. The two never differ by more than a second, so 09:00 UTC and 09:00 GMT are the same moment.
How do I pick a meeting time that works for three time zones?
Put all three zones on the list and try times in the zone with the most awkward spread, usually the one furthest east or west. Change the hour until every row lands between about 8:00 and 18:00. When the spread is more than about 14 hours no slot fits everyone, so rotate the early or late call between people.
Why do some zones have half hour or 45 minute offsets?
Countries choose an offset that matches local daylight or a neighbour. India is UTC+5:30, Newfoundland is UTC-3:30, and Nepal is UTC+5:45, with the Chatham Islands of New Zealand at UTC+12:45 outside summer. The tool handles these exactly, since it reads the offset from the zone database rather than assuming whole hours.
Do all countries use daylight saving time?
No. Most of Asia, Africa and South America keep one offset all year, as do Queensland and the Northern Territory in Australia and Arizona in the United States. The European Union has debated ending clock changes for years without settling it. Using IANA zone names rather than fixed offsets keeps all of this correct automatically.
Does the converter know where I am?
It reads only the time zone your device is set to, through a browser setting that every page can see, to fill in the starting zone. It does not use location services, and the zone name never leaves the page. Nothing you add to the list is stored, so the next visit starts fresh.
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Background reading: the question page on this.
Written and checked by the OneCraft team. Last checked .