How this calculator works
Every place on Earth reads the same instant as a different wall-clock time because its time zone is an offset from UTC. The offset can change through the year where daylight saving time is observed, so a zone is not a single fixed number. This page uses the IANA time zone database, which records the rules for each named zone and the dates on which they changed. A local time is first turned into an instant using the source zone offset, then the instant is rendered in each destination zone with the offset that is in force at that moment.
Formula
instant = local wall time minus the source offset. destination wall time = instant plus the destination offset. The offset is shown as UTC plus or minus whole hours, or hours and minutes where a half-hour zone applies, such as UTC+5:30 for India. Daylight saving adds one hour for the months in which a zone observes it.
Worked example
12:00:00 in Toronto on 1 January 2026 is 17:00:00 UTC, because Eastern Standard Time is UTC-5. The same instant is 12:00 in London, 13:00 in Paris, 17:30 in Kolkata, 21:00 in Tokyo and 23:00 in Sydney. In July, Toronto uses UTC-4 and the same local noon is 16:00 UTC.
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Frequently asked questions
Why is the offset different in summer and winter?
Daylight saving time moves the clock forward by an hour for part of the year in many zones. The page looks up the rule for the date you enter, so the offset shown matches that date rather than a single annual value.
What happens at a daylight saving gap?
When clocks spring forward, a local time such as 02:30 may not exist. The page detects that the entered time cannot be reached in the source zone and asks for another time instead of guessing.
What happens during the autumn overlap?
When clocks fall back, a local time such as 01:30 occurs twice. The page chooses one of the two instants using the zone rules; the converted outputs then refer to that instant. A wall-clock time alone cannot distinguish the two.
Are the zone names and rules fixed forever?
No. Governments change offsets and daylight saving dates from time to time. The IANA database is updated when those changes are announced, and the browser running this page supplies the rules it has.