ISO Week Number
Look up an ISO 8601 week number, week-based year and weekday for any date.
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What is ISO Week Number?
ISO Week Number identifies the ISO 8601 week, week-based year and weekday for a calendar date.
How to use ISO Week Number
- 01
Choose the date you want to classify.
- 02
Review whether its ISO week-based year differs from its calendar year near New Year.
- 03
Copy the ISO week label and numeric details.
ISO Week Number FAQ
Why can January 1 belong to the previous ISO year?
The ISO week-based year follows complete Monday-to-Sunday weeks, so dates near New Year can belong to an adjacent week-year.
Is ISO Week Number private to use?
Yes. Date, time and schedule calculations run locally in your browser and are not sent to Toolnera.