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Excel WEEKNUM Function

Excel WEEKNUM function

The Excel 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. 

Get the week number for a given date
Return value 
A number between 1 and 54.
=WEEKNUM (serial_num, [return_type])
  • serial_num - A valid Excel date in serial number format.
  • return_type - [optional] The day the week begins. Default is 1.
Usage notes 

The WEEKNUM function starts counting with the week that contains January 1. The return_type argument controls which day of the week is used to begin a new week number. Return_type is optional and defaults to 1.

With a return_type of 1-17, week number 1 in a given year is assigned to the week that contains January 1. With return_type 21, week 1 is the week containing the first Thursday of the year, following ISO 8601.

Return_type Week begins
1 (default) Sunday
2 Monday
11 Monday
12 Tuesday
13 Wednesday
14 Thursday
15 Friday
16 Saturday
17 Sunday
21 Monday (see note above)


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