Week Number Calculator
Find the week number of any date.
Result
ISO week numberExample
Week 44
of 2026
- Week runs
- Mon, 26 Oct 2026 to Sun, 1 Nov 2026
- ISO week date
- 2026-W44-6
- Day of the year
- 304
- Weeks in 2026
- 53
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Questions
What is an ISO week number?
ISO 8601 weeks start on Monday, and week 1 is the week with the year’s first Thursday (so it always contains 4 January). A year has 52 or 53 of them. Most of Europe and much of the world uses this.
Why can early January be in week 52 or 53?
Because the ISO week belongs to the year that holds most of its days. 1 January 2027 is a Friday, so it is in week 53 of 2026.
How does US numbering differ?
US weeks start on Sunday and week 1 is the week containing 1 January, however short. Spreadsheet WEEKNUM functions use this by default.
Is it free? Do I need an account?
It is free to use and there is nothing to sign up for. There are no watermarks and no daily limits.
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