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ISO Week Number Calculator

Find the ISO week number, week-year and weekday.

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  1. 01

    Add your input

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  2. 02

    Make it yours

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  3. 03

    Take the result

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ISO 8601 week calculator online

Check the week identifier used in a weekly report. ISO week-year can differ from calendar year near January and December boundaries.

How to use it

Enter Date (YYYY-MM-DD) or select Try example. Review the displayed input. Select Run tool and inspect the result before copying or downloading.

Worked examples

Check the week identifier used in a weekly report.

Worked example — ISO Week Number Calculator

Settings: No additional options

Input:

2026-10-10

Output:

2026-W41-6

Limitations and common mistakes

  • ISO week-year can differ from calendar year near January and December boundaries.

Frequently asked questions

How can I locate the ISO week number online?

Enter Date (YYYY-MM-DD) or select Try example. Review the displayed input. Select Run tool and inspect the result before copying or downloading.

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.

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