Creating a custom Week Number variable in a date table

[jcpewittyancey]

Hi all. I need to create a Week Number column in a date table, but the WEEKNUM function doesn't produce quite the right results.

For the purposes of this variable, weeks start on Sunday. The part where it gets tricky is around the end/beginning of a year.

If the last Sunday of the year falls on December 29, 30, or 31, then I need the following set of 7 days (including the last Sunday in December) to be assigned a week number of 1. If the last Sunday of December falls on December 25, 26, 27, or 28 I need the following set of 7 days (including the last Sunday of December) to be assigned to week 52 or 53 or 54 or whatever is appropiate that year. The end result is that fo some years, there will be some dates in December assigned to week 1, and in other years there will be some days in January that are assigned to week 52 or 53 or 54.

Here are a couple examples of what the output should be:

Day	Date	Week Number
Saturday	12/29/2018	52
Sunday	12/30/2018	1
Monday	12/31/2018	1
Tuesday	1/1/2019	1
Wednesday	1/2/2019	1
Thursday	1/3/2019	1
Friday	1/4/2019	1
Saturday	1/5/2019	1
Sunday	1/6/2019	2

Day	Date	Week Number
Saturday	12/26/2015	52
Sunday	12/27/2015	53
Monday	12/28/2015	53
Tuesday	12/29/2015	53
Wednesday	12/30/2015	53
Thursday	12/31/2015	53
Friday	1/1/2016	53
Saturday	1/2/2016	53
Sunday	1/3/2016	1

I appreciate any help!

[LivioLanzo · Accepted solution]

try adding a calculated column with this formula

=WEEKNUM( [Date] + 1, 21 )

[AlB · Accepted solution]

@Anonymous 

This will answer your question:

https://dax.guide/weeknum/

Please mark the question solved when done and consider giving a thumbs up if posts are helpful.

Contact me privately for support with any larger-scale BI needs, tutoring, etc.

Cheers 

[LivioLanzo · Accepted solution]

try adding a calculated column with this formula

=WEEKNUM( [Date] + 1, 21 )

[Anonymous]

Hi @LivioLanzo ,

Thanks for the solution, this has helped me as well.

I would like to know the logic behind 21, as i could see while typing the formula, we have the option of only 1 (sunday) and 2(Monday).

Thanks in advance.

Regards,

Pavan

[jcpewittyancey]

Wow, that was remarkably simple! Thanks so much!