Week Number Calculator — ISO Week of Any Date
Find the ISO week number for any date
How to Use Week Number Calculator
Find the ISO week number for any date No signup, and nothing gets uploaded for most use.
- 1
Enter your numbers in the input fields.
- 2
Choose the calculation options or frequency.
- 3
The result updates instantly as you type.
- 4
Review the breakdown, chart, or schedule, and copy the answer.
Why you might like it
- Nothing to upload — the work happens on your device.
- Free with no signup, no watermarks, and no daily limits.
- Works in any modern browser on any device — nothing to install.
- Usually done in a few seconds, so it doesn't get in your way.
Frequently Asked Questions
What is an ISO week number?▾
ISO 8601 numbers weeks so week 1 is the week containing the first Thursday of the year. This means the first week can start in the previous calendar year.
Why can the ISO year differ from the calendar year?▾
Days near January 1 can belong to week 52 or 53 of the previous year, or week 1 of the next year, so the ISO year may differ from the calendar year for those dates.
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