Everyday Life · Time & Date
Timezone Converter
Convert a time from one timezone to another by applying UTC offsets.
Calculator
Formula
T_source is the source time in hours, UTC_target is the target timezone offset in hours from UTC, and UTC_source is the source timezone offset in hours from UTC. The result is adjusted modulo 24 to stay within a valid 24-hour range.
Source: ISO 8601 / IANA Time Zone Database standard.
How it works
Every timezone is defined by its offset from Coordinated Universal Time (UTC). For example, New York (EST) is UTC−5 and Paris (CET) is UTC+1. To convert between them, you calculate the difference in offsets and add it to the source time.
The result is taken modulo 24 hours (or 1440 minutes) to handle rollovers past midnight or before midnight, ensuring the output is always a valid time of day. Note that this calculator does not account for Daylight Saving Time (DST) automatically — you should manually adjust offsets when DST is in effect.
Worked example
Suppose it is 14:30 in New York (UTC−5) and you want to know the time in London (UTC+0).
Offset difference = 0 − (−5) = +5 hours.
Target time = 14:30 + 5:00 = 19:30 in London.
Now suppose it is 23:00 in Tokyo (UTC+9) and you want the time in Los Angeles (UTC−8). Offset difference = −8 − 9 = −17 hours. 23:00 − 17:00 = 6:00, so it is 06:00 in Los Angeles.
Limitations & notes
This calculator uses fixed UTC offsets and does not automatically apply Daylight Saving Time rules, which vary by country and year. Always verify current DST status for the relevant regions. It also does not track date changes — a result past midnight or before midnight represents the next or previous calendar day respectively, which this tool does not display explicitly.
Frequently asked questions
What is a UTC offset?
A UTC offset is the difference in hours (and sometimes half-hours) between a local timezone and Coordinated Universal Time. For example, UTC+5:30 is used in India.
How do I account for Daylight Saving Time?
Manually adjust the UTC offset by +1 hour when DST is in effect for that region. For example, Eastern Time shifts from UTC−5 (EST) to UTC−4 (EDT) during summer.
What if my result shows a time past 23:00 or before 00:00?
The calculator wraps results using modulo 1440 minutes, so the time always stays within 00:00–23:59. However, this means the result may fall on the next or previous calendar day.
Can I use half-hour or quarter-hour offsets?
Yes — enter offsets as decimals, such as 5.5 for UTC+5:30 (India) or 9.75 for UTC+9:45 (parts of Australia). The calculator handles non-integer offsets correctly.
What is the difference between UTC and GMT?
GMT (Greenwich Mean Time) and UTC are effectively the same for everyday timekeeping purposes. UTC is the modern scientific standard, while GMT is the historical predecessor still commonly referenced.
Last updated: 2025-01-15 · Formula verified against primary sources.