🗓️Week Number Calculator
ISO week number for any date.
About the Week Number Calculator
Find the ISO 8601 week number and day of the year for any date. Useful for scheduling, reporting and project planning. Free online week number calculator.
How to use the Week Number Calculator
- 1Pick your date(s) or time(s) in the Week Number Calculator above.
- 2Adjust any options for your calculation.
- 3Read the result instantly.
- 4Runs entirely in your browser.
Why use this tool?
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Private by design
The Week Number Calculator runs entirely in your browser — nothing you enter is uploaded to a server.
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Free, no signup
Use it as much as you like. There's no account, no paywall and no watermark.
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Fast & instant
Results appear the moment you type or click — no waiting, no page reloads.
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Works anywhere
Any device or browser, even offline once the page has loaded.
Frequently asked questions
Which week-numbering standard is used?＋
ISO 8601, where weeks start on Monday and week 1 contains the year's first Thursday. It also shows the day of the year.