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Excel ISOWEEKNUM Function

Excel ISOWEEKNUM function
Summary 

The Excel ISOWEEKNUM function takes a date and returns a week number (1-54) that follows ISO standards, where weeks begin on Monday and week number 1 is assigned to the first week in a year that contains a Thursday.

Purpose 
Get ISO week number for a given date
Return value 
A number between 1 and 54.
Syntax 
=ISOWEEKNUM (date)
Arguments 
  • date - A valid Excel date in serial number format.
Usage notes 

The ISOWEEKNUM function returns a week number based on ISO standards. Under this standard, weeks begin on Monday and the week number 1 is assigned to the first week in a year that contains a Thursday.