How to create date from week and year colums in powerquery?

Hi sylvianelissen,

I realise Fowmy just replied, but just adding an option I had been looking at.

If you are using ISO Weeks, you would need to implement something like this:

https://www.ablebits.com/office-addins-blog/excel-weeknum-function-convert-week-number-date/#convert-week-number-date

In Power Query, you could create a function to do the conversion:

//fn_YearWeeknumToWeekStartDate
(Year as number, #"Week Number" as number) as date =>
  let
    Jan01           = #date(Year, 1, 1),
    Jan03           = #date(Year, 1, 3),
    Jan03_DayOfWeek = Date.DayOfWeek(Jan03, Day.Sunday),
    WeekStartDate   = Date.AddDays(Jan01, - Jan03_DayOfWeek + #"Week Number" * 7 - 4)
  in
    WeekStartDate

Below is a sample query to test the above function:

let
  Source = #table(
    type table [Jaar = Int64.Type, Weeknummer = Int64.Type],
    {{2025, 1}, {2025, 2}, {2025, 3}, {2025, 4}}
  ),
  #"Added Week Start Date" = Table.AddColumn(
    Source,
    "Week Start Date",
    each fn_YearWeeknumToWeekStartDate([Jaar], [Weeknummer]),
    type date
  )
in
  #"Added Week Start Date"