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How to Use Excel WEEKNUM Function?

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WEEKNUM Function in Excel: Usually, we planned for events like birthday parties, an inaugural for an organization, or any other occasions on specific days or weeks. On that note, if you are a regular Excel user, then you can plan for these kinds of occasions using the Excel function called WEEKNUM.

This function returns a week number from the specific date value. It is one of the built-in functions in Excel.

In this short tutorial, we will show you an explanation, syntax, and usage of the WEEKNUM function in Excel with practical examples. Get the official version of MS Excel from the following link:

Use WEEKNUM FunctionPin
Use WEEKNUM Function

Explanation of WEEKNUM Function

  • The WEEKNUM Function in Excel takes the date as an input and returns the week number (1 to 54).
  • This function will start to count the week from January 1.
  • Make use of this function to calculate how many weeks we have been crossed since from January 1 to the present date.


  • In this section, you will see the syntax of the WEEKNUM Function.
  • To apply this function on your spreadsheet, you have to select a cell and enter the formula in the following format.
  • Once you enter the formula, just click on the Enter button to get the week number based on your input value.

=WEEKNUM(serial_number, [return_type])

Argument Description

  • Serial_number (Required): The date for which you need to get the week number.
  • Return_type (Optional): A number that identifies the return value type.


Return_typeWeek Starts onSystem
1 or omittedSunday1


  • System 1: The first week of the year is considered from January 1 and it is numbered as week 1.
  • System 2: The first week of the year is considered from the first Thursday of the year and it is numbered as week 1. This kind of system is mentioned in ISO 8601 and also referred to as the European week numbering system.


1) MS Excel stores the dates as sequential numbers and so it can be utilized in calculations. By default,

  • January 1, 1900 – serial number 1
  • January 1, 2008 – serial number 39448 (because it is 39,448 days after Jan 1, 1900)

2) #NUM! error – if the serial_number or return_type is out of range, then the function returns this error.

Practical Examples

Let’s look at some practical examples of the WEEKNUM Function and explore how to use it in Microsoft Excel.

  • Initially, you have to open your Excel workbook on your PC and launch a worksheet that has data.
  • The input value is entered into the B2 cell, as shown in the below screenshot.
Input data
Input data
  • We can use the following formula to find the WEEKNUM value. We have entered the formula in Cell D2 and hit the Enter button.


Enter the formula
Enter the formula
  • After executing the formula, we will get the result, as shown in the below image.
  • In this example 1, we did not mention the return_type so the function takes the default value 1.
  • As per the System 1, January 1 is considered to be the first week of the year. So, 09/03/2020(Monday – March 9th) is the 11th week starting from the first week on January 1.
  • Let’s see another example to make it clear.
  • The above steps need to be repeated for this example, so it will display the below output.
  • In this example, we have chosen the return_type as 13, but it comes under system 1, so the output will not differ because of the change in return_type.

A Brief Summary

In this short tutorial, we have illustrated how to use WEEKNUM Function in Excel with detailed practical examples. If you have any queries/doubts, kindly share them in the below comment section. If you want to learn more about Excel functions, then visit our webpage

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