Week Number In Excel

Updated on April 22, 2024
Article byJeevan A Y
Edited bySheeba M
Reviewed byDheeraj Vaidya, CFA, FRM

What Is Week Number In Excel (WEEKNUM)?

WEEKNUM or Week Number in Excel is a Date & Time function that gives us the week number for the given date. We know that we have an average of 52 weeks in a year for 12 months. So, for a particular date, the Excel Week Number helps us find the specific week number.

For example, for the dates given below in cells A1:A7, when we apply the WEEKNUM Excel function for the cell B1, and then drag the formula using the fill handle to the rest of the cells, i.e., to cells B1:B7, we will get the output shown below.

Week Number In Excel

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Key Takeaways

  • The Week Number in Excel helps users retrieve the precise serial number of the week of a specific date out of the approximate 52 weeks per year.
  • We use the WEEKNUM function that has two arguments:
    • The first which is mandatory takes valid date.
    • The second argument is optional, which represents the day on which the week begins.
  • The start of the year, Jan 01, will always be the first week of the year, and Dec 31 will always be the last week of the year, the 52nd week.
  • We have 10 different options to supply at the start of the week. Since this is an optional argument, we need not mandatorily supply the argument. However, if we leave this argument blank, by default, the value will be 1, i.e., the start of the day of the week is Sunday.

Syntax Of WEEKNUM Function In Excel

The syntax of the WEEKNUM formula is,

WEEKNUM Formula in Excel

The arguments of the WEEKNUM formula is,

  • serial_numberIt is the date for which we find the week number. Excel treats DATE as a serial number.
  • return_typeWe need to mention the start of the weekday.

Download Template

This article must help understand Week Number in Excel with its formulas and examples. You can download the template here to use it instantly.

You can download this WEEKNUM Function Excel Template here – WEEKNUM Function Excel Template

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How To Use The Week Number (WEEKNUM) Function In Excel?

We can use the WEEKNUM function in Excel as follows:

First, choose an empty cell – select the “Formulas” tab – go to the “Function Library” group – click the “Date & Time” option drop-down – select the “WEEKNUM” function, as shown below.

WEEKNUM” function


We will consider some examples to use the WEEKNUM Function in Excel.

Example #1 – Finding Week Number in Excel

We have the below dates and must find the Excel Week Number for each date in that particular year.

Week Number Example 1

The steps to find the Week Number are as follows:

  1. Open the Excel WEEKNUM function in the B2 cell.

    Open the Excel WEEKNUM function in the B2 cell

  2. The serial_number is nothing but your date cell. So, select A2 as the cell reference.

    select A2 as the cell reference

  3. As of now, ignore the last argument. By default, it will take Sunday as the starting day of the week.

    ignore the last argument

  4. Drag the formula to other cells.

    Drag the formula to other cells

  5. We got week numbers for respective dates. But look at the cells A2 and A3; both are on 30th Nov but of a different year. Since Excel considers the start of the week from Sunday, it will vary year to year.

    look at the cells A2 and A3

  6. Now, let us change the start of the week to MONDAY.

    change the start of the week to MONDAY

  7. We can mention the argument as 2. Close the formula.

    mention the argument as 2

  8. The result is shown below:

    The result is shown below

  9. Apply to other cells by dragging the formula.

    Apply to other cells by dragging the formula

    We do not see any differences here. Try changing the starting day of the week to a different date and find the differences.

Example #2 – Add the Word WEEK to the Week Number in Excel

We have seen how to return the week number of any supplied date. It will be clearer to add the word “Week” before the week’s number, like in the image below.

WEEKNUM Example 2

It is where the advanced formatting technique in excelFormatting Technique In ExcelFormatting is a useful feature in Excel that allows you to change the appearance of the data in a worksheet. Formatting can be done in a variety of ways. For example, we can use the styles and format tab on the home tab to change the font of a cell or a table.read more comes into the picture. Follow the below steps to apply the above formatting.

  • Step 1: Select all the result cells first.
WEEKNUM Example 2
  • Step 2: Right-click on the selected cells and select “Format Cells”.
WEEKNUM Example 2-1.1
  • Step 3: Now, we will see the format dialog box. Go to “Custom” first.
WEEKNUM Example 2-1
  • Step 4: Enter the format code “Week”# in the Type: field.
WEEKNUM Example 2-2
  • Step 5: Press “OK”. We will have results ready.
WEEKNUM Example 2-3

Instead of changing the formatting of the cells, we can also combine the word “Week” with the result cells. Refer to the image to apply the same.

WEEKNUM Example 2-4

Example #3 – Calculate Number of Weeks in excel between Two Dates

We have learned the technique of finding the week number. But, how to tell how many weeks are between two dates?

If we have started the project on 15th Jan 2018, and completed it on 30th April 2018, as shown below.

WEEKNUM Example 3

The steps to calculate the weeks taken to complete the project are,

  • Step 1: Firstly, find the difference between the two dates.
WEEKNUM Example 3-1
  • Step 2: Now, divide the difference by 7. We have 7 days a week.
WEEKNUM Example 3-2
  • Step 3: Press the “Enter” key to complete the formula. We have a result like this.
WEEKNUM Example 3-3
  • Step 4: Change the format to “General” for accurate results.
WEEKNUM Example 3-4

Example #4 – Calculate the Number of Weeks in Fraction using Excel

Let us consider one more example to have a clear idea about finding the week’s number between two dates in Excel.

Suppose we are going on a business trip from 15th Feb 2018 and are returning on 30th Jun 2018. The business head decided to pay the money weekly.

WEEKNUM Example 4

Let us apply the formula we used in the previous example to find the difference between the two dates.

WEEKNUM Example 4-1

Now, divide the difference by 7. So, we have 7 days a week.

WEEKNUM Example 4-2

We have a result like this.

WEEKNUM Example 4-3

Let us change the format of the resulting cell to fractions.

WEEKNUM Example 4-4

So, we have the number of weeks in fractions now.

WEEKNUM Example 4-5

Important Things To Note

  • By default, the start of the week in Excel is SUNDAY.
  • We must supply the return type correctly to start with a different week.
  • If the date is not in the correct format, we may get #VALUE! error.

Frequently Asked Questions (FAQs)

1. How to open the “Format Cells” window to custom the Week Number format?

There are various methods to open the Format Cells window, namely,
Method 1 Simply press the shortcut key “Ctrl+1”.
Method 2 Select the “Home” tab – go to the “Number” group – click the “Number Format” option drop-down – select the last option “More Number Formats…”, as shown below.

Custom Number Format in Excel - More Number Format

Method 3 Right-click on any cell, and select the “Format Cells…” option from the list, as shown below.

Format Cell

Method 4 Select the “Home” tab – go to the “Number” group – click the “Number Format” box, i.e., the small box at the bottom right of the “Number” group, as shown below.

Number Format

2. Why is the WEEKNUM formula not working?

A few reasons why the WEEKNUM formula may not work are,
• The cell reference given for the argument is not a valid date.
• We have given the date value directly as an argument, and have not enclosed it in double-quotes. So, we get the “#NUM!” error.
• The result becomes 0 when we delete the dataset, or there are empty or blank cells.

3. How can we enter the WEEKNUM formula directly in the worksheet?

The steps to enter the WEEKNUM formula directly in the worksheet are,
Step 1: Choose an empty cell for the output.
Step 2: Type =WEEKNUM( in the cell. [Alternatively, type =W or =WEEK and select the WEEKNUM function from the Excel suggestions.]
Step 3: Enter the arguments as cell value or cell reference and close the brackets.
Step 4: Press the “Enter” key to get the output.

This article is a guide to Week Number in Excel. Here we find serial number of Week for a given date, WEEKNUM formula, examples & a downloadable excel template. You may learn more about Excel from the following articles: –