MasterTool

Time Zone Converter

Convert a date and time between 40+ IANA time zones — daylight saving handled automatically by the built-in timezone database.

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What this tool does

Convert a date and time between 40+ IANA time zones — daylight saving handled automatically by the built-in timezone database. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.

How to use the Time Zone Converter

  1. Enter or select date and time (yyyy-mm-ddthh:mm).
  2. Enter or select from time zone.
  3. Enter or select to time zone.
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

the entered wall-clock time is resolved to a UTC instant using the source zone's offset from the browser's built-in Intl/IANA database (iterated twice so DST transitions resolve correctly), then re-rendered in the destination zone; the time difference is destination offset − source offset
datetime
Date and time (YYYY-MM-DDTHH:MM)
from
From time zone
to
To time zone

Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.

Worked example

For time zone converter, the following measurements illustrate the exact method: Date and time (YYYY-MM-DDTHH:MM): 2026-06-01T12:00; From time zone: America/New_York; To time zone: Europe/London.

Inputs

  • Date and time (YYYY-MM-DDTHH:MM)2026-06-01T12:00
  • From time zoneAmerica/New York
  • To time zoneEurope/London

Result

  • Converted time (Europe/London)2026-06-01 17:00
  • Converted dayMonday, June 1, 2026
  • Source UTC offsetUTC-04:00
  • Destination UTC offsetUTC+01:00
  • Time difference (hours)5
  • Same moment in UTC2026-06-01 16:00 UTC

Results explained

Converted time (Europe/London)
Converted time (Europe/London) from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.
Converted day
Converted day from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.
Source UTC offset
Source UTC offset from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.
Destination UTC offset
Destination UTC offset from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.
Time difference (hours)
Time difference (hours) from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.
Same moment in UTC
Same moment in UTC from the formula above. Uses only the IANA timezone database built into your browser via Intl.DateTimeFormat — no API and no live data. Offsets are correct for the entered date, including DST. Historical dates use the rules recorded in that database.

Frequently asked questions

Offsets are looked up for the exact date you enter in the IANA database built into your browser, so a New York noon converts to 17:00 in London during British Summer Time but 17:00 can become a different gap in the weeks when the US and UK change clocks on different weekends.

Several zones use half-hour or 45-minute offsets — India is UTC+05:30, Nepal UTC+05:45, St. John's UTC−03:30 (standard time). The difference output keeps those fractions exactly.

No. Everything runs locally with Intl.DateTimeFormat, which ships the full IANA timezone database in every modern browser. That is also why conversions work offline and for historical dates.

Yes — crossing enough zones or the International Date Line moves the calendar date. The converted day output shows the weekday and full date at the destination so a next-day or previous-day result is obvious.

It is the time as shown on a clock in that zone on that date — 12:00 in New York means local noon there, whatever the UTC offset happens to be that day. The tool resolves that local reading to one exact UTC instant before converting.