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Date & Time

Time Zone Converter

Pick a source and target city, enter a clock time (24h), and instantly see what time it is on the other side — including the offset difference, whether the date rolls over, and the matching UTC timestamp. 30+ common cities, with DST handled automatically.

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Time difference

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UTC

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Zone data comes from the system IANA tz database — DST changes and historical offsets are handled automatically. If the entered time falls into a DST "spring-forward" gap, the calculator resolves it to the closest valid instant.

Formula

instant_utc = wall_time − offset(source_zone, wall_time) target_clock = instant_utc + offset(target_zone, instant_utc) DST transitions resolved via the IANA tz database (built into the runtime).

Frequently asked

What is the difference between GMT, UTC and HKT?

UTC (Coordinated Universal Time) is the current international time standard, maintained by atomic clocks and occasionally adjusted by leap seconds. GMT (Greenwich Mean Time) was originally based on mean solar time at the Royal Observatory; in everyday use it is essentially identical to UTC and still appears in British contexts and some legacy zone labels. HKT (Hong Kong Time) is UTC+8 year-round — Hong Kong has not observed DST since 1979.

Why does daylight saving time shift the difference each year?

North America, most of Europe and parts of Australia shift clocks forward by 1 hour in summer for longer evening daylight. For example, New York is UTC−5 in winter (EST) and UTC−4 in summer (EDT), so the difference vs. Hong Kong (a fixed UTC+8) is 13 h in winter but 12 h in summer. The exact switch dates differ — US / Canada: 2nd Sunday of March (spring forward) and 1st Sunday of November (fall back); Europe: last Sunday of March and last Sunday of October. This tool applies the correct rule for the date you enter.

Why does the target date sometimes jump forward or back a day?

When the time gap exceeds the hour-of-day, the target falls on the previous or next calendar day. Example: Hong Kong 5 Jan 10 pm (HKT) maps to New York 5 Jan 9 am EST — same day. But Hong Kong 5 Jan 1 am maps to New York 4 Jan noon — one day earlier. The tool flags this with a "one day later / earlier" hint next to the target time.

Can I pick any city — mine is not in the list?

The default list includes 30+ commonly used cities covering most populated zones. If your city is not listed, pick another city in the same IANA zone (e.g. Bangkok / Hanoi / Jakarta share UTC+7 timing rules; Sydney / Melbourne / Canberra share Australia/Sydney).

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