Useful Utilities

Time Zone Converter

Convert a date and wall-clock time from any timezone or city to another zone, returning the target wall clock, the day change and the daylight-saving-correct GMT offsets for that exact date.

Fill in the values and calculate

From zone*City entries are shortcuts to that city's zone; anything else is an exact zone name
To zone*The zone whose wall clock you want
Date at the source*Year-month-day, or words like today and tomorrow
Time at the source (24-hour)*Wall clock at the source zone, HH:MM

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About Time Zone Converter

Your time is first placed on the source zone's calendar: a search over whole-minute offsets pins the exact UTC instant where that source zone's own clock reads your input, which is where daylight-saving switchovers actually happen. That instant is then read back through the target zone, so a date straddling a DST change shows the offset the target holds on that day rather than today's.

Every offset is minutes away from UTC (GMT+1 is +60, GMT-4 is -240). The day change is the count of local calendar dates separating the two clocks. A zone's standard offset is taken as whichever of its January and July offsets is smaller, and any larger offset on the chosen date is reported as daylight saving.

City shortcuts are just the built-in city list's zone names. Offsets before 1970 or after rule changes the zone table has not caught up with may be wrong, because time-zone rules are local law, not geometry; the bisection only resolves whole-minute offsets.

Questions about Time Zone Converter

Why does the offset change with the date?

Because offsets are resolved for the exact date entered: the two zones are read where daylight saving actually is on that day, so the same pair converts differently in January and in July.

What is the day change?

How many local calendar dates the target is ahead of or behind the source. Long eastward hops land tomorrow; westward ones land yesterday.

Does it know future daylight-saving changes?

Only what the zone table on your system contains. Governments change rules with little notice, so very distant dates can be wrong.

Can I pick a place that is not on the city list?

Yes. Every zone name in the full list works; the city entries are only shortcuts to their zones.

What if my time falls in a skipped hour?

Spring-forward clock changes skip an hour that never exists. The tool keeps the closest real instant and explains that in the notes.

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