Excel Functions

Excel WEEKNUM Function

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The WEEKNUM function takes a date and returns a week number (1-54) that corresponds to the week of year. The WEEKNUM function starts counting with the week that contains January 1. By default, weeks begin on Sunday.

Purpose of Excel WEEKNUM Function

Get the week number for a given date.

Return value

A number between 1 and 54.


=WEEKNUM (serial_num, [return_type])


serial_numA valid Excel date in serial number formatMandatory
return_typeThe day the week begins. Default is 1Optional

Usage notes

  • Excel stores dates as sequential serial numbers so they can be used in calculations.
  • By default, January 1, 1900 is serial number 1.
  • January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900.
  • If Serial_number is out of range for the current date base value, a #NUM! error is returned.
  • If Return_type is out of the range specified in the table above, a #NUM! error is returned.


Since 2007 for Windows.
Since 2011 for Mac.

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