ISOWEEKNUM Function

The Excel ISOWEEKNUM function will retrieve the integer number from 1 to 52, representing the ISO week number for a specified date. This function uses the European ISO standard 8601:2000 to get the week numbering, which considers the year's first week to contain the first Thursday. It is categorized under the Date & Time functions in Excel. This function is not supported in the older version of Excel, which was first launched in Excel 2013.

Compatibility

This advanced Excel function is compatible with the following versions of MS Excel −

Excel for Microsoft 365
Excel for Microsoft 365 for Mac
Excel for the web
Excel 2024
Excel 2024 for Mac
Excel 2021
Excel 2021 for Mac
Excel 2019
Excel 2016
Excel 2013

Syntax

The syntax of the ISOWEEKNUM function is as follows −

=ISOWEEKNUM(date)

Arguments

You can use the following arguments with the ISOWEEKNUM function −

Argument	Description	Required / Optional
Date	It specifies the date-time code, which can be used in the other formula for future calculations.	Required

Points to Remember

In Microsoft Excel, Dates are stored as serial numbers that ease the analyst's use in complex calculations. By default, serial number 1 indicates January 1, 1900, and serial number 40990 indicates March 3, 2012.
If the date argument contains an invalid number, then the ISOWEEKNUM function will retrieve the #NUM! error.
If the date argument specifies the invalid date type, then the ISOWEEKNUM function will return the #VALUE! error.
In the older versions of Excel before Excel 2010, the ISO week number can be computed using the WEEKNUM function by setting the return_type argument to 21. For example: WEEKNUM(serial_number, 21).

How to use the ISOWEEKNUM Function in Excel?

Step-by-step explanations are depicted below −

First, deliberate an Excel worksheet, and a list of the dates is written in the specified column.
After that, double-click on the targeted cell and write the formula =ISOWEEKNUM("cell reference that refers to the date").
Finally, hit the Enter to get the ISO week number.

Example of ISOWEEKNUM Function in Excel

Practice the following example to learn how to use the ISOWEEKNUM function in Excel.

How to get the ISO Week Number from Date in Excel?

This example facilitates users in obtaining the ISO week number by applying the ISOWEEKNUM function in the specific range of the cells.

Solution

Step 1 − First, consider the sample dataset, which comprises two columns named Date and ISOWEEKNUM- the independent date serial numbers are specified in the cell range B3:B6.

Get the ISO Week Number from Date in Excel1

Step 2 − After that, select the cell range C2:C5 and write the formula =ISOWEEKNUM(C2) in the formula bar.

Get the ISO Week Number from Date in Excel2

After that, press the "Ctrl+ Enter" to populate the results in this cell range.

Get the ISO Week Number from Date in Excel3

Step 3 − If you wish to extract the ISO week number of today's date, write the expression =ISOWEEKNUM(TODAY()) in the C7 cell and then press the Enter tab.

Get the ISO Week Number from Date in Excel4

Therefore, today's date is 07/01/2025, and the resulting value is 2, which denotes the current week of 2025.

Download Practice Sheet

You can download and use the sample data sheet to practice the ISOWEEKNUM function.

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