fnGetIsoWeekNumber.pq

(MyDate as date) =>
      //Source --> https://blogs.office.com/en-us/2009/06/30/week-numbers-in-excel/
    let
      //MyDate = #date(2016,1,3),
      Part1 = Number.From(MyDate) - Number.From(#date(Date.Year(Date.From(Number.From(MyDate) - (Date.DayOfWeek(Date.AddDays(MyDate,-1), Day.Sunday) + 1) + 4)),1,3)),
      Part2 = Date.DayOfWeek(#date(Date.Year(Date.From(Number.From(MyDate) - (Date.DayOfWeek(Date.AddDays(MyDate,-1), Day.Sunday) +1) + 4)),1,3), Day.Sunday)+1 + 5,
      ISOWeekNumber = Number.IntegerDivide(Part1 + Part2, 7)
    in
      ISOWeekNumber