About the Time Zone Calculator
A time zone calculator converts a time from one UTC offset to another. It is the calculation behind scheduling a meeting across countries, and getting it wrong is one of the most common coordination failures in distributed work.
The formula
Target time = source time − source offset + target offsetUTC offsets range from −12 to +14 hours. Most are whole hours, but India is +5:30, Nepal +5:45, and parts of Australia +8:45 or +9:30.
How to use this calculator
- 1Enter your Hour (0–23). The field starts at
12, which you can overwrite. - 2Enter your Minute (0–59). The field starts at
0, which you can overwrite. - 3Enter your Your UTC Offset (e.g. -5 for EST, +5.5 for IST). The field starts at
0, which you can overwrite. - 4Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Hour (0–23) | 12 |
| Minute (0–59) | 0 |
| Your UTC Offset (e.g. -5 for EST, +5.5 for IST) | 0 |
Result
UTC: 12:00 PM
EST (New York): 7:00 AM
CST (Chicago): 6:00 AM
MST (Denver): 5:00 AM
PST (Los Angeles): 4:00 AM
GMT (London): 12:00 PM
CET (Paris): 1:00 PM
IST (Mumbai): 5:30 PM
CST (Beijing): 8:00 PM
JST (Tokyo): 9:00 PM
AEST (Sydney): 10:00 PM
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
Converting through UTC is the reliable method: subtract the source offset to reach UTC, then add the target offset. Attempting to compute the difference between two zones directly invites sign errors, particularly when one is ahead of UTC and the other behind.
Daylight saving is what makes time zones genuinely hard. Offsets change on dates that differ between countries, the southern hemisphere shifts in the opposite direction from the northern, and some places do not observe it at all. New York and London are usually five hours apart but four for a few weeks each spring, because the two switch on different dates.
Things worth knowing
- Always convert via UTC rather than computing a difference between two local times directly.
- Not all offsets are whole hours — India is +5:30 and Nepal +5:45.
- The gap between two cities changes during the weeks when one has switched to daylight saving and the other has not.
- The International Date Line means some zones are on a different calendar day, not just a different hour.
- For scheduling, state the time zone explicitly and prefer UTC or an IANA zone name over abbreviations like CST, which are ambiguous.
Frequently asked questions
How do I convert between time zones?+
Subtract the source UTC offset to get UTC, then add the target offset. Going through UTC avoids the sign errors that direct differences invite.
What is UTC?+
Coordinated Universal Time, the global reference from which all time zones are defined as offsets. It does not observe daylight saving, which is why it is used as the anchor.
Why do time zone differences change during the year?+
Because daylight saving start and end dates differ between countries, and the southern hemisphere shifts in the opposite direction. New York and London are five hours apart most of the year but four for a few weeks in spring.
Do all time zones use whole hours?+
No. India is UTC+5:30, Nepal is UTC+5:45, and parts of Australia use +8:45 or +9:30. Assuming whole hours is a common source of scheduling errors.