How to Convert Between Time Zones Using UTC Offsets
Converting a time between two cities is confusing when you think in terms of "hours ahead" and "hours behind", because the direction is easy to flip. A cleaner approach is to pass every conversion through one common reference: UTC, Coordinated Universal Time. Every time zone is described as an offset from UTC, so two additions or subtractions get you anywhere.
This guide gives the method, shows a full worked example across five zones, covers offsets that are not whole hours, and explains how to find a sensible meeting time for people in several places.
The two-step method
A time zone's offset says how far its local clock is from UTC. New York in winter is UTC−5, so its clock is 5 hours behind UTC. Tokyo is UTC+9, so its clock is 9 hours ahead. Then:
UTC = local time − offset; target local time = UTC + target offsetSubtracting a negative offset means adding.
Worked example: it is 15:00 on Tuesday 12 January 2027 in New York (UTC−5).
- To UTC: 15:00 − (−5) = 15:00 + 5 = 20:00 UTC.
- To Tokyo (UTC+9): 20:00 + 9 = 29:00, which is 05:00 the next day.
- To India (UTC+5:30): 20:00 + 5:30 = 25:30, which is 01:30 the next day.
| Place | Offset in January | Local time when New York shows 15:00 Tue |
|---|---|---|
| New York | UTC−5 | 15:00 Tue |
| London | UTC+0 | 20:00 Tue |
| India | UTC+5:30 | 01:30 Wed |
| Tokyo | UTC+9 | 05:00 Wed |
| Sydney | UTC+11 | 07:00 Wed |
Sydney is on summer time in January, which is why its offset is UTC+11 rather than its winter value of UTC+10. Whenever the result goes past 24:00, subtract 24 and move the date forward by one day; if it goes below 00:00, add 24 and move the date back.
Offsets that are not whole hours
Most offsets are whole hours, but not all. India is UTC+5:30 all year, Nepal is UTC+5:45 and parts of Australia use half-hour offsets. Treat the minutes like any other minutes: convert 20:00 UTC to Nepal time and you get 20:00 + 5:45 = 25:45, or 01:45 the next day.
The offsets in use run from UTC−12 to UTC+14, a spread of 26 hours, so two places can be on different calendar dates at the same moment. Tokyo and New York are 14 hours apart in January, so for 14 hours of every day Tokyo's date is a day ahead. Always include the date when you send a converted time to someone.
Finding a meeting time that works
To schedule across zones, convert each person's available hours to UTC and look for the overlap.
Worked example: a team in London (UTC+0 in winter) and one in New York (UTC−5), both available 09:00 to 17:00 local time.
- London 09:00 to 17:00 is 09:00 to 17:00 UTC.
- New York 09:00 to 17:00 is 14:00 to 22:00 UTC (add 5 to each).
- The overlap is 14:00 to 17:00 UTC, which is 14:00 to 17:00 in London and 09:00 to 12:00 in New York.
Add a third team in Tokyo (UTC+9), available 09:00 to 17:00 local, which is 00:00 to 08:00 UTC. There is no overlap with London at all, since London starts at 09:00 UTC. Someone in that group has to start early or stay late, and the fair way to decide is to rotate the burden.
Writing times so nobody misreads them
A time without a zone is ambiguous, and abbreviations do not always help. IST can mean India, Irish or Israel Standard Time, and CST can mean US Central, China or Cuba Standard Time. Better options:
- Name the place: "15:00 New York time on 12 January".
- State the offset: "15:00 UTC−5".
- Use UTC with a date, such as 2027-01-12 20:00 UTC, in international schedules.
- In data and software, use the full ISO form, for example 2027-01-12T20:00:00Z, where the Z means UTC.
One more caution: many regions change their offset during the year for daylight saving time, and they do not all change on the same date. The offsets in this article apply to the dates shown, so always check them for the date you are converting. The article on daylight saving time and 23- or 25-hour days shows how the gap between two cities can shift.
The time zone converter applies the right offset for any date, and the 24-hour to 12-hour converter helps when a schedule is written on a different clock style.
- Time Zone Converter: Enter a date and time, choose the zone it is in and the zone you want, and read the converted time in your own locale format and on a 24 hour clock.
- 24 Hour to 12 Hour Time Converter: Choose a direction, type a time such as 17:30 or 5:30 PM, and the converted time appears underneath. The chart below lists all 24 hours for a quick lookup.
This article is general information, not professional advice. See our Disclaimer and Editorial Policy.
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