Which standard does this use?

ISO 8601: week 1 is the week containing the first Thursday of the year. Weeks start on Monday.

Week Number Calculator

Find the ISO week number (1–53) for any date.

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How to use this tool

Enter date in the fields above.
Results update instantly as you type — or click Calculate.
Read your iso week number and the full breakdown beneath it.

Find the ISO week number (1–53) for any date.

Frequently asked questions

Which standard does this use?: ISO 8601: week 1 is the week containing the first Thursday of the year. Weeks start on Monday.