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Timezone Offset Transition Finder

Find timezone UTC-offset changes in a selected calendar year using browser timezone data.

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Find timezone UTC-offset changes in a selected calendar year online

Find timezone UTC-offset changes in a selected calendar year using browser timezone data. Use this to inspect or plan dates and time windows from explicit reference values. Fixed examples make the result independent of the date on which this page is opened.

How to use it

Enter a value or text in the format shown in the example. Set iana timezone. Choose Run tool. Review the output, then copy or download it.

Options and example settings

Option	Choices / value	Example default
IANA timezone	Enter iana timezone.	Europe/Tirane

Worked examples

Use this to inspect or plan dates and time windows from explicit reference values. Fixed examples make the result independent of the date on which this page is opened.

Reproducible worked example

Settings: IANA timezone: Europe/Tirane

Input:

With the input and settings above, the tool produces:

Output:

[
  {
    "instantUTC": "2026-03-29T01:00:00.000Z",
    "beforeOffsetMinutes": 60,
    "afterOffsetMinutes": 120
  },
  {
    "instantUTC": "2026-10-25T01:00:00.000Z",
    "beforeOffsetMinutes": 120,
    "afterOffsetMinutes": 60
  }
]

The example returns 2 top-level items in an array. Each item is a record; the first record contains “instantUTC”, “beforeOffsetMinutes”, “afterOffsetMinutes”.

Limitations and common mistakes

Uses the browser’s installed timezone database and a three-hour scan with minute refinement, for years 1970–2100. It does not fetch current law or certify historical transition completeness.
Combined input is bounded to 150,000 characters; output text is bounded to 1.2 million characters. Some algorithms impose smaller limits, stated in their error messages.

Frequently asked questions

What format should I enter?

Enter a value or text in the format shown in the example. The worked example shows the supported structure and actual output.

How can I locate timezone UTC-offset changes in a selected calendar year online?

Enter a value or text in the format shown in the example. Set iana timezone. Choose Run tool. Review the output, then copy or download it.

Where is my input processed?

The bundled tool processes input in your browser. It does not upload tool input to a conversion service. Other site plugins, analytics, advertising and browser extensions may have separate behavior.