Week Number Calculator
Find the ISO 8601 week number for any date, the dates that week runs from Monday to Sunday, and the day of the year.
This tool runs entirely in your browser.
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How to use the Week Number Calculator
- 1Pick a date (today by default).
- 2Read the ISO week number and week dates.
What is the Week Number Calculator?
ISO weeks start on Monday, and week 1 is the week containing the year’s first Thursday. Because of this, 1 January can belong to week 52 or 53 of the previous year.
Frequently asked questions
Do the US and Europe number weeks differently?
Often, yes. Europe uses ISO weeks (Monday start); many US calendars start weeks on Sunday and count 1 January as week 1.
Is the Week Number Calculator free and private?
Yes. The Week Number Calculator is free, needs no account, and runs entirely in your browser. What you type is never sent to a server or stored.
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