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Time Zone Converter

Converts a wall-clock date and time from one IANA time zone to another using the tz database rules built into ICU, so the daylight-saving offsets in force on that date are applied automatically. Reports both UTC offsets, the UTC instant, the weekday and the day difference.

When to use

You need to know what time an event scheduled in one city corresponds to in another city or in UTC on a specific date.

Do not use when: You need the same instant in many zones at once (use world-clock), an epoch value (use unix-timestamp), or the elapsed time between two clock times (use time-duration).

Formula

utc = date + time − offset_from(date, time); converted = utc + offset_to(utc); time_difference_hours = (offset_to − offset_from) / 60

Offsets come from the IANA tz database as shipped with ICU (Intl.DateTimeFormat), including historical and future daylight-saving rules known at build time. A source time that does not exist because clocks jumped forward is moved forward by the gap; a time that occurs twice during a fall-back hour takes its first occurrence.

Inputs

Parameter	Type	Required	Description
`date`	date	default today	Calendar date of the source time in from_zone (YYYY-MM-DD); defaults to the current UTC date.
`time`	string	yes	Wall-clock time in from_zone, 24-hour HH:MM (seconds optional).
`from_zone`	string	yes	IANA time zone of the source time, e.g. Australia/Adelaide, Europe/Berlin or UTC.
`to_zone`	string	yes	IANA time zone to convert to, e.g. America/New_York or Asia/Tokyo.

Outputs

Output	Type	Unit	Description
`converted_date`	date		Calendar date in to_zone.
`converted_time`	string		Wall-clock time in to_zone (HH:MM).
`converted_datetime`	string		ISO 8601 date-time in to_zone including its UTC offset.
`converted_weekday`	string		Day of the week of converted_date.
`from_utc_offset`	string		UTC offset of from_zone at that instant (±HH:MM).
`to_utc_offset`	string		UTC offset of to_zone at that instant (±HH:MM).
`from_abbreviation`	string		Short zone name from ICU (e.g. EDT); 'GMT+9:30' style when the zone has no common English abbreviation.
`to_abbreviation`	string		Short zone name of to_zone at that instant.
`utc_datetime`	string		The same instant in UTC (ISO 8601).
`day_difference`	integer	days	converted_date minus date: −1, 0 or +1.
`time_difference_hours`	number	h	to_zone offset minus from_zone offset at that instant; positive when to_zone is ahead.

Example

09:00 Adelaide → New York on 2026-09-23: {"date":"2026-09-23","time":"09:00","from_zone":"Australia/Adelaide","to_zone":"America/New_York"} → {"converted_date":"2026-09-22","converted_time":"19:30","converted_weekday":"Tuesday","from_utc_offset":"+09:30","to_utc_offset":"-04:00","utc_datetime":"2026-09-22T23:30:00Z","day_difference":-1,"time_difference_hours":-13.5}

12:00 Los Angeles → Kolkata on 2026-07-04: {"date":"2026-07-04","time":"12:00","from_zone":"America/Los_Angeles","to_zone":"Asia/Kolkata"} → {"converted_date":"2026-07-05","converted_time":"00:30","from_utc_offset":"-07:00","to_utc_offset":"+05:30","utc_datetime":"2026-07-04T19:00:00Z","day_difference":1,"time_difference_hours":12.5}

GET https://tttkmbb.com/api/v1/calculate/time-zone-converter?date=2026-09-23&time=09%3A00&from_zone=Australia%2FAdelaide&to_zone=America%2FNew_York

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/time-zone-converter (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/time-zone-converter · Markdown: https://tttkmbb.com/time/time-zone-converter.md · JSON definition: https://tttkmbb.com/time/time-zone-converter.json
MCP: server https://tttkmbb.com/mcp, tool convert_time_zone
OpenAPI operationId: convert_time_zone
Freshness: daily. Authentication: none. Rate limit: fair use (see rate limits).

Sources

IANA Time Zone Database (tz) (standard)
List of tz database time zones (Wikipedia) (reference)

FAQ

Which zone names are accepted?

IANA names such as Europe/Paris, America/Chicago, Asia/Singapore or Australia/Perth, plus UTC and fixed zones like Etc/GMT+5 (note the reversed sign). Abbreviations such as 'CST' are ambiguous and mostly not accepted.

How is daylight saving handled?

Automatically: the offset of each zone on the given date is looked up in the tz database, so a 9:00 Adelaide meeting in September lands at 19:30 the previous evening in New York, but at 18:30 once Adelaide starts daylight saving in October.

Related calculators

World Clock Calculator — Show one instant in a whole list of cities.
Unix Timestamp Converter — Turn the same instant into Unix epoch seconds.
Time Duration Calculator — Hours and minutes between two clock times.