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CALCPARK

Time Zone Converter

Convert a date and time between any two time zones, with each zone’s UTC offset and daylight-saving status, plus a four-zone meeting planner for overlapping hours.

Runs on your device
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How to use it

  1. Pick the date and time, or press Now. Your browser’s zone is preselected as the source.
  2. Choose the source and target zones – common cities first, then every IANA zone; type the first letters to jump.
  3. Read the converted time with the day (previous/next when the date changes), the abbreviation, the UTC offset and whether DST applies in each zone.
  4. Add up to four zones to the meeting planner: the 24-hour strip shows each zone’s local hours, with 09:00–17:59 shaded, so overlapping working hours stand out.
  5. Copy the result or the link; the link carries the date, time and zones.

Example

Monday 19 October 2026, 09:30 in London (BST, UTC+1) is 04:30 in New York(EDT, UTC−4), 17:30 in Tokyo (JST, UTC+9) and 19:30 in Sydney (AEDT, UTC+11) – the difference to New York is −5 h. The same London time on 5 April 2026 is 03:30 in New York: London is already on BST while the US has been on daylight time since 8 March, so the gap is 5 hours; between 8 and 29 March it was only 4.

How the conversion works

instant (UTC) = wall time in source zone − offset(source zone, instant)
target wall time = instant + offset(target zone, instant)

The browser formats a trial instant in the source zone, the difference between that wall clock and UTC gives the offset, and the instant is refined until the wall clock matches the input (three steps at most). Offsets are then read for the target zone and the planner zones at that same instant, so daylight-saving changes on either side are handled by the IANA rules rather than by fixed numbers.

A wall time inside a spring-forward gap (02:30 on the night clocks jump from 02:00 to 03:00) does not exist; the tool moves it to the next valid minute and says so. A time inside an autumn overlap exists twice; the first occurrence (still on daylight time) is used. “DST” means the offset is larger than the zone’s standard offset for that year, which works for both hemispheres. Abbreviations are the browser’s English names (BST, EDT, GMT+9) and can differ between browsers for less common zones.

Dates from 1900 to 2100 are accepted; historical rules before about 1970 are only partly recorded in the database, and future DST rules can change by law. Zones with a 30- or 45-minute offset (India, Nepal, Newfoundland, central Australia) are shown with minutes, e.g. UTC+5:30.

Sources: IANA Time Zone Database, MDN – Intl.DateTimeFormat and timeZone, Daylight saving time by country.

Questions

What is the time difference between EST and GMT?
Five hours in winter (EST is UTC−5, GMT is UTC±0). In summer both sides move: New York is on EDT (UTC−4) and London on BST (UTC+1), so the gap is still five hours – except for the few weeks in spring and autumn when only one of them has switched.
Why does the result show the previous or next day?
When the offset difference carries the time past midnight the date changes: 19:00 Monday in Los Angeles is 11:00 Tuesday in Tokyo. The caption flags it, and the planner marks such hours in the cell tooltip.
Which zone should I pick for “Central Time” or “IST”?
Pick the city: America/Chicago for US Central Time, Asia/Kolkata for India Standard Time, Europe/Dublin for Irish Standard Time. Abbreviations are reused across continents, which is why the tool lists IANA city names instead.
Does the converter need an internet connection for the rules?
No. The time zone rules are part of your browser (the IANA database it ships with), so conversions run locally and work offline once the page is open.