The WEEKNUM formula in Excel is an effective tool used to determine the week number of a specific date in a year, with weeks starting on Sunday or Monday.


The purpose of the WEEKNUM formula is to facilitate chronological organization and data analysis in Excel. It allows users to arrange or group data based on the week of the year, a task useful in various professional fields such as project management and logistics.


The syntax for creating a WEEKNUM formula in Excel is straightforward:

=WEEKNUM(serial_number, [return_type])


The WEEKNUM formula requires the following parameters:

  • serial_number: This is the date for which you want to find the week number. It is a required parameter.
  • return_type: This optional parameter determines the day on which the week begins. If it’s omitted, Excel defaults to 1 (week begins on Sunday).


The WEEKNUM formula yields an integer from 1 to 53 representing the week number of the year for the specified date.

Usage Notes

The WEEKNUM formula only considers the date portion of a datetime value. For optimal results, your input data should be in a format that Excel can identify as a date or datetime.


The WEEKNUM formula is accessible across all versions of Excel, becoming a vital part of the spreadsheet calculator toolkit.

Example #1

Assume that the date “2023-06-23” resides in cell A1. To find the week number, use:


Given that June 23, 2023, falls in the 25th week of the year, the formula will return 25.

Example #2

If you want the week to start on Monday, use the return_type parameter. If “2023-06-24” is in cell A1:


This will return 26, as June 24, 2023, also falls in the 26th week of the year.

Example #3

For datetime values like “2023-06-23 18:00:00” in cell A1, the WEEKNUM formula overlooks the time portion:


The formula will return 25, which represents the 25th week.

Example #4

For invalid dates like “Hello” in cell A1:


Excel will return a #VALUE! error, indicating the input is not a valid date.

Example #5

WEEKNUM can process dates in text format. With “2023-06-23” in cell A1:


The result will be 25, as June 23, 2023, is in the 25th week.

Tips and Tricks

Keep in mind that the WEEKNUM formula extracts the week number from a date. It doesn’t return the actual date.


WEEKNUM cannot process text that isn’t a valid date and will return a #VALUE! error.

Common errors and solutions

The #VALUE! error occurs when the serial_number parameter is not a valid date. Always verify that your date inputs are valid.

Best Practices

Always cross-check your date data to make sure it’s valid. Use the return_type parameter to control the first day of the week according to your needs.

List of Related Functions

Related functions for Excel include:

  • DATE: Converts a year, month, and day into a date.
  • DAY: Extracts the day of the month from a date.
  • MONTH: Extracts the month from a date.
  • YEAR: Extracts the year from a date.

Frequently Used with the Formulas

WEEKNUM is commonly used alongside other date and time functions such as DATE, DAY, MONTH, and YEAR.

Frequently Asked Questions

Q. What is the range of return values for the WEEKNUM formula?

The WEEKNUM formula returns an integer ranging from 1 to 53, representing the week number of the year.

Q. How does Excel determine the first day of the week in the WEEKNUM formula?

By default, Excel sets Sunday as the first day of the week. However, you can change this by using the return_type parameter.

Q. Can I use WEEKNUM with time values?

Yes, but WEEKNUM only considers the date part of a datetime value. The time part is ignored.

Master the art of Excel formulas and functions, especially WEEKNUM, to make your data analysis tasks efficient and reliable.

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