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How to Use The WEEKNUM Function in Google Sheets

Google Sheets has a number of useful date functions that can be used to do many different things.

One useful built-in date function in the WEEKNUM function.

In this tutorial, I will show you how to use the WEEKNUM function in Google Sheets.

WEEKNUM Syntax

The WEEKNUM function takes a date and returns a number that represents the week of the year for which that date is.

The syntax of the WEEKNUM function is:

=WEEKNUM(date, [type])

  • date – this is the date that will be used to return the week number.
  • type – this is an optional argument that is set to 1 by default. It’s a number that tells Google Sheets which day the week starts on (1=Sunday, 2=Monday, etc.). The accepted values for this parameter are:
    • 1/omitted – Week begins on Sunday, ends on Saturday
    • 2 – Week begins on Monday, ends on Sunday
    • 11 – Week begins on Monday, ends on Sunday
    • 12 – Week begins on Tuesday, ends on Monday
    • 13 – Week begins on Wednesday, ends on Tuesday
    • 14 – Week begins on Thursday, ends on Wednesday
    • 15 – Week begins on Friday, ends on Thursday
    • 16 – Week begins on Saturday, ends on Friday
    • 17 – Week begins on Sunday, ends on Saturday
    • 21 – Week begins on Monday, ends on Sunday

There are two numbering systems used for weeks in this function

  • System 1 – the first week of the year is the week containing January 1st.
  • System 2  – The first week of the year is the week containing the first Thursday of the year. This is called the European system or ISO 8601. Type 21 is this system

Using WEEKNUM

Now that I have gone over the basic syntax of this function, let’s take a look at how to actually use it in your spreadsheet.

All you need to do is enter the date into the function and the type if desired. Here are some examples:

WEEK NUM

You can see in the example above that the WEEKNUM function is pretty simple to do. I just have the cell reference containing the date inside the function and it returns the week number.

In the example, I have the first two cells with the “type” argument omitted, which means these will count the weeks as type 1.

In the second two cells, I have type 21. Notice how it returns January 1st as a different week number than type 1.

Closing Thoughts

The WEEKNUM function is useful if you are regularly dealing with date data and need to get the week number from a date.

It is a very simple formula with a good amount of customization on how weeks are counted.

Hopefully, you found this tutorial helpful!

More Google Sheets Tutorials:
How to Insert Current Date
How to Use the ISDATE Function