A time zone converter answers what a given local clock time is in another city: the time is shifted to UTC using the source zone's offset, then shifted again by the destination zone's offset. Offsets are read live from the IANA time zone database for today's date, so daylight saving is already applied, and the result flags when it lands on the next or previous day.
Meeting planner
Shaded = 9am–6pm · green column = everyone’s working · today’s date
9aUTC-4
2pUTC+1
Daylight saving is applied for today
Offsets come from the IANA time-zone database for today's date. A time months out can land on the other side of a DST switch — London is UTC+1 in July but UTC+0 in January — shifting London by an hour.
Check the day shift before you schedule
Crossing into the next or previous day is the classic scheduling slip. If London's time carries a "next day" or "previous day" note, the meeting isn't on the day you'd assume. Pair with Countdown for time until the call.
Ask a follow-up
Uses your inputs above
14:00 in london. Want to try a variation?
Type a question below to compare scenarios.
The math
Reviewed 2026
Formula
UTC = local − from_offset; destination = UTC + to_offset (offsets read live from the IANA tz database, DST included)
Daylight saving is applied for today's date; a time months away may fall on the other side of a DST change
Time Zone Converter uses the formula shown in the math card and cites IANA Time Zone Database. Inputs are validated for sensible ranges; results are computed client-side for instant feedback and do not leave your browser.
How do I convert a time between two time zones by hand?
Subtract the source zone's UTC offset from the local time to get UTC, then add the destination zone's offset. If the result crosses midnight, wrap it around 24 hours — the clock time is right but it falls on the neighboring day.
What does it mean that a city is hours ahead?
A zone is ahead when its UTC offset is larger, so its clocks show a later time. Tokyo at UTC+9 is 9 hours ahead of London at UTC+0: when it is 15:00 in London, Tokyo's clocks already read midnight.
Does this handle daylight saving time?
Yes. Offsets come from the IANA database evaluated for today's date, so a city on summer time shows its DST offset — London reads UTC+1 in July and UTC+0 in January. A time set months away could still fall on the other side of a DST switch.
Why can the converted time land on a different day?
The converter shows clock time only, so a result that wraps past midnight belongs to the next or previous calendar day — the card labels which. New York at 9:00 AM is 10:00 PM the same day in Tokyo, while a late-evening start can roll into tomorrow.
What does this calculator assume?
Daylight saving is applied for today's date; a time months away may fall on the other side of a DST change See the math card above for the full list.
How accurate is this time zone calculator?
The math is deterministic — the same inputs always produce the same output, and the formula is shown above. Accuracy of the answer for your situation depends on how well your inputs match reality and how well the formula models the question.