World Time Zone Converter
Convert any local time to its equivalent in another time zone, with automatic daylight saving time adjustments built in. Ideal for scheduling calls, flights, or events across international locations.
About this calculator
Converting between time zones requires knowing each zone's UTC offset — a fixed number of hours (and sometimes half-hours) added to or subtracted from Coordinated Universal Time (UTC). The core formula is: Target Time = (sourceHour + sourceMinute/60 + targetOffset − sourceOffset + dstAdjustment + 24) % 24, where the modulo 24 operation wraps the result into a valid 0–23 hour range. DST adds +1 hour to the source zone (dstAdjustment = 1), −1 hour to the target zone (dstAdjustment = 2), or both (dstAdjustment = 3). For example, UTC+0 to UTC+5:30 requires adding 5.5 to the source time. The +24 before the modulo prevents negative results from large westward conversions.
How to use
Suppose it is 14:45 in London (UTC+0) and you want the time in Tokyo (UTC+9), with no DST active. Enter sourceHour = 14, sourceMinute = 45, sourceOffset = 0, targetOffset = 9, dstAdjustment = 0. The calculator computes: (14 + 45/60 + 9 − 0 + 0 + 24) % 24 = (14.75 + 9 + 24) % 24 = 47.75 % 24 = 23.75, which equals 23:45 — meaning it is 11:45 PM in Tokyo when it is 2:45 PM in London.
Frequently asked questions
How does daylight saving time affect time zone conversion calculations?
Daylight saving time (DST) shifts a region's clocks forward by one hour in spring and back in autumn. When converting times, you must account for whether the source zone, the target zone, both, or neither is currently observing DST. In this calculator, dstAdjustment = 1 adds one hour (source observes DST), dstAdjustment = 2 subtracts one hour (target observes DST), and dstAdjustment = 3 applies both. Ignoring DST can cause a one-hour error in your converted time, which matters greatly for international meetings or flight connections.
What is a UTC offset and how is it used in time zone conversion?
A UTC offset expresses how many hours (and sometimes 30 or 45 minutes) a time zone differs from Coordinated Universal Time (UTC). For example, UTC+5:30 means local time is 5 hours and 30 minutes ahead of UTC. To convert between two zones, you simply add the difference between their offsets to the source time. UTC offsets range from UTC−12:00 (Baker Island) to UTC+14:00 (Line Islands). Half-hour and quarter-hour offsets exist in places like India (UTC+5:30) and Nepal (UTC+5:45).
Why does the conversion formula use modulo 24 and add 24 before dividing?
The modulo 24 operation (% 24) wraps any result outside the 0–23 hour range back into a valid time of day, since a clock cycles every 24 hours. Adding 24 before taking the modulo is a safeguard against negative intermediate values: if your source is UTC+8 and your target is UTC−5, the raw difference is −13, which would produce a negative hour without the +24 buffer. This ensures the formula always returns a non-negative result. It is a standard technique in circular arithmetic used throughout time-keeping software.