How to convert weekly dates to fortnightly dates

[Michaelc1993]

Hi Everyone,

Its my first post in the forum so apologies if the post is posted incorrectly.

I want to convert weekly dates to fortnightly dates. While this sounds simple - I cant seem to get it working. I know there was a similar post: https://community.powerbi.com/t5/DAX-Commands-and-Tips/Grouping-dates-into-fortnights/m-p/949837 but this didnt quite work for me as the numbers didn't while line up.

This is the data I have which goes up to 2023 (see below). I essentially want the 'Fortnight' column to show 06/01/21 for the first period. Then from 7/01/21 - 20/01/21 to show as 20/01/21 and 03/02/21 for the next 2 week period and so on.

I intially tried 

"Fortnight =

VAR __BaseDate = DATE(2021,1,6)

VAR __2w = (__BaseDate) +14

RETURN

if(Dates[Date]<=__BaseDate,__BaseDate,__2w)"

but ovbiously this only works for the first period. wondering if some sort of loop could be made using this? or another simpler method altogether? 

Any help would be greatly appreciated!

Kind regards,

Mike

[amitchandak · Accepted solution]

@Michaelc1993 , Try a new column like

New column
VAR __BaseDate = DATE(2021,1,6)
return
quotient(datediff(__BaseDate,[Date],day),14) +1

if we need a yearly reset, we have start using week year start date, in place of DATE(2021,1,6)

Week Start date = 'Date'[Date]+-1*WEEKDAY('Date'[Date],2)+1

Week Start Year = minx(filter('Date',[Year] =earlier([Year])),[Week Start date])