How to use the WEEKNUM function
Author: Oscar Cronquist Article last updated on November 02, 2018
The WEEKNUM function calculates a given date's week number based on a return_type parameter that determines which day the week begins.
Formula in cell D3:
=WEEKNUM(B3,C3)
You also have the option to choose which system to use, see the [return_type] argument.
| System 1 | Week 1 is the week that contains January 1. |
| System 2 | Week 1 is the week that contains the first Thursday of the year. (European week numbering system). |
Excel Function Syntax
WEEKNUM(serial_number,[return_type])
Arguments
| serial_number | Required. A date. If you enter the date in the function then use the DATE function to calculate the correct serial_number. |
| [return_type] | Optional. A number determining which day the week begins. If omitted, 1 is used. |
The following table shows what the LOGEST function returns if [stats] argument is TRUE.
| [return_type] | Week starts on | System |
| 1 | Sunday | 1 |
| 2 | Monday | 1 |
| 11 | Monday | 1 |
| 12 | Tuesday | 1 |
| 13 | Wednesday | 1 |
| 14 | Thursday | 1 |
| 15 | Friday | 1 |
| 16 | Saturday | 1 |
| 17 | Sunday | 1 |
| 21 | Monday | 2 |
Comments
The WEEKNUM function returns #NUM! error if:
- serial_number is out of range.
- [return_type] is out of range.
'WEEKNUM' function examples
Count unique distinct values within same week, month or year
The array formula in cell E3 counts unique distinct items for all dates within the same week. Example, week 2 […]
The array formula in cell E3 counts unique distinct items for all dates within the same week. Example, week 2 […]
Filter duplicates within same date, week or month
The image above demonstrates a formula in cell E3 that extracts duplicate items if they are on the same date. […]
The image above demonstrates a formula in cell E3 that extracts duplicate items if they are on the same date. […]
Highlight a date occuring [Conditional formatting]
Excel has a built-in feature that allows you to highlight dates if a given condition is met. Section 1 below […]
Excel has a built-in feature that allows you to highlight dates if a given condition is met. Section 1 below […]
Functions in this article
Functions in 'Date and Time' category
The WEEKNUM function function is one of many functions in the 'Date and Time' category.
Returns a number that acts as a date in the Excel environment.
Returns the number of days, months, or years between two dates. The DATEDIF function exists in order to ensure compatibility with Louts 1-2-3.
Returns an Excel date value (serial number) based on a date stored as text.
Extracts the day as a number from an Excel date.
Calculates the number of days between two dates.
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Returns a decimal number based on a text string.
Returns the Excel date (serial number) of the current date.
Converts a date to a weekday number from 1 to 7.
Calculates a given date's week number based on a return_type parameter that determines which day the week begins.
Returns a date based on a start date and a given number of working days (nonweekend and nonholidays).
Converts a date to a number representing the year in the date.
Returns the fraction of the year based on the number of whole days between a start date and an end date.
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Allows you to filter data based on selected value , a given text, or other criteria. It also lets you filter existing data or move filtered values to a new location.
Lets you control what a user can type into a cell. It allows you to specifiy conditions and show a custom message if entered data is not valid.
Lets the user work more efficiently by showing a list that the user can select a value from. This lets you control what is shown in the list and is faster than typing into a cell.
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VBA stands for Visual Basic for Applications and is a computer programming language developed by Microsoft, it allows you to automate time-consuming tasks and create custom functions.
A program or subroutine built in VBA that anyone can create. Use the macro-recorder to quickly create your own VBA macros.
UDF stands for User Defined Functions and is custom built functions anyone can create.
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