ISO Week Number Finder

ISO 8601 week number and week-year for any date — the business standard.

Date:

How to use

Pick a date and click Find.

What is an ISO week?

Weeks start Monday; week 1 is the week with the first Thursday. Early January can belong to the previous year's week 52/53.

Why does the year differ sometimes?

ISO week-year follows the week, not the month — Jan 1 can be in week 52 of the prior ISO year.

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