How to use Excel WEEKNUM Function


WEEKNUM function in Excel is a type of DATE/TIME function. This function converts a date into a number from 1 to 54 which represents number of the week. By default, first day of the week is Sunday. This function can also be used with other functions for inserting the day of the week.


=WEEKNUMS(Serial_Number, Return_Type)


  • Serial_Number: It is the date for which number of the week needs to be found.
  • Return_Type: It is the number which represents week mapping scheme. Its default value is 1


  • In General formatting of Excel, Dates are in form of serial numbers. Serial number 1 is for 1 JAN, 1900 and the number increases from thereon. For getting it in readable form use the formatting tab.
  • The argument used must represent a valid date in Excel format.
  • If the arguments used have number values which are out of range of valid excel date, #NUM error is displayed
  • If the arguments used have strings which cannot be converted into valid dates, #VALUE error is displayed.


Return type Week Begins
1 Sunday-Saturday
2 Monday-Sunday
3 Monday-Sunday
11 Monday-Sunday
12 Tuesday-Monday
13 Wednesday-Tuesday
14 Thursday-Wednesday
15 Friday-Thursday
16 Saturday-Friday
17 Sunday-Saturday


In this example, dates are given in column A and WEEKNUM function is used to retrieve number of the week in column B for the corresponding date:

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