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Week Number of the Year

Enter a date to determine the week number of the year according to your selected standard.

Calculation Standard

Week starts on Monday. First week contains the first Thursday of January.

Week starts on Sunday. First week contains January 1.

Date:

Total weeks in year:

Please enter a valid date

Calculation Standards

ISO 8601 Standard

Week start: Monday.

First week rule: The first week of the year is the one containing the first Thursday of January (or at least 4 days of the new year).

Traditional / US (from January 1)

Week start: Sunday.

First week rule: The first week of the year is the one containing January 1.

This calculator determines the week number for any calendar date.

Week numbering is not universal – it depends on the standard used. Two main approaches are used worldwide, and both are implemented in this calculator.

After selecting a date and standard, you will see: