Time Zone Converter
Convert a wall-clock time from one UTC offset to another, with the day shift shown explicitly.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
A time zone is just a fixed offset from UTC, so converting a time between two zones is a single addition: take the time you have, add the difference between the two offsets, and read the result off a 24-hour clock. When that addition carries past midnight or back before it, the clock wraps around and the date moves too — which is why the day shift is reported separately instead of being hidden inside the time. Use HH:MM or separate hour and minute fields. This compares fixed UTC offsets, not named time zones; daylight-saving changes must be supplied in the chosen offsets.
Worked example
calculated with the default values below
Time input HH:MM · Source time (HH:MM) 09:00 · Source UTC offset UTC+00:00 · Target UTC offset UTC+08:00 · Hours 9 · Minutes 0 Converted time 17:00 · Day shift 0 days · Difference between zones 8.00 hours
General background references
Disclaimer
These calculators give general date results. Public holidays, working-day conventions and time-zone rules are set locally and change, so confirm against the official calendar for anything legally or contractually binding.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
T = 60h + m + 60(U − F); t = T mod 1440; d = ⌊T ÷ 1440⌋
- h,m
- Source hour, minute
- F
- Source UTC offset
- U
- Target UTC offset
- d
- Day offset
Input must be HH:MM with 00–23 h and 00–59 min; t is formatted back to HH:MM.
Frequently asked questions
Where do the offsets come from?
From the time zone you select, expressed as a fixed offset from UTC. Offsets are not permanently fixed, because many regions change them for daylight saving and can change the rules at short notice. For anything scheduled more than a few weeks ahead, confirm the offset that will be in effect on the date itself rather than the one in force today.
How do I avoid mistakes with a meeting across several zones?
Quote the time in UTC as well as in each local zone, and state the date. Quoting only a local clock time leaves both sides guessing whose clock is meant, which is how the wrong hour gets into a calendar invitation. Distributing the UTC time alongside the local ones gives everyone a single unambiguous reference.