WEEKNUM DAX Function (Date and Time)
Returns the week number in the year.
Syntax
WEEKNUM ( <Date> [, <ReturnType>] )
| Parameter | Attributes | Description |
|---|---|---|
| Date |
A date in datetime format. |
|
| ReturnType | Optional |
A number that determines the return value: for example, use 1 when week begins on Sunday, or use 2 when week begins on Monday, or use 21 for ISO week numbers. More details in Remarks section. |
Return values
Scalar A single integer value.
The week number for the given date.
Remarks
If the argument is a string, it is translated into a datetime value using the same rules applied by the DATEVALUE function.
There are two systems used for this function:
- System 1 The week containing January 1 is the first week of the year, and is numbered week 1.
- System 2 The week containing the first Thursday of the year is the first week of the year, and is numbered as week 1. This system is the methodology specified in ISO 8601, which is commonly known as the European week numbering system.
| Return_type | Week begins on | System |
|---|---|---|
| 1 or omitted | 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 |
Examples
--
-- WEEKNUM returns the week number following different standards
--
EVALUATE
ADDCOLUMNS (
TOPN ( 10, VALUES ( 'Date'[Date] ), 'Date'[Date], ASC ),
"Day of week", FORMAT ( 'Date'[Date], "dddd" ),
"WEEKNUM", WEEKNUM ( 'Date'[Date] ) , -- Same as 1, week start on Sun
"WEEKNUM 2", WEEKNUM ( 'Date'[Date], 2 ), -- Week start on Mon
"WEEKNUM 11", WEEKNUM ( 'Date'[Date], 11 ), -- 11 to 17: 1st DOW Mon
"WEEKNUM 12", WEEKNUM ( 'Date'[Date], 12 ), -- 11 to 17: 1st DOW Tue
"WEEKNUM 13", WEEKNUM ( 'Date'[Date], 13 ), -- 11 to 17: 1st DOW Wed
"WEEKNUM 21", WEEKNUM ( 'Date'[Date], 21 ) -- ISO 8601 Week
-- (1st thursday of the year)
)
ORDER BY 'Date'[Date]
| Date | Day of week | WEEKNUM | WEEKNUM 2 | WEEKNUM 11 | WEEKNUM 12 | WEEKNUM 13 | WEEKNUM 21 |
|---|---|---|---|---|---|---|---|
| 2005-01-01 | Saturday | 1 | 1 | 1 | 1 | 1 | 53 |
| 2005-01-02 | Sunday | 2 | 1 | 1 | 1 | 1 | 53 |
| 2005-01-03 | Monday | 2 | 2 | 2 | 1 | 1 | 1 |
| 2005-01-04 | Tuesday | 2 | 2 | 2 | 2 | 1 | 1 |
| 2005-01-05 | Wednesday | 2 | 2 | 2 | 2 | 2 | 1 |
| 2005-01-06 | Thursday | 2 | 2 | 2 | 2 | 2 | 1 |
| 2005-01-07 | Friday | 2 | 2 | 2 | 2 | 2 | 1 |
| 2005-01-08 | Saturday | 2 | 2 | 2 | 2 | 2 | 1 |
| 2005-01-09 | Sunday | 3 | 2 | 2 | 2 | 2 | 1 |
| 2005-01-10 | Monday | 3 | 3 | 3 | 2 | 2 | 2 |
Related functions
Other related functions are:
Last update: Jun 14, 2025 » Contribute » Show contributors
Contributors: Alberto Ferrari, Marco Russo
Microsoft documentation: https://docs.microsoft.com/en-us/dax/weeknum-function-dax
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