Weeknummer / Jaar naar datum

Public Function daynumber(weeknumber, dag)
  
iYear = 2009
iWeekday = dag

iWeek = weeknumber + 1

fnDateFromWeek = _
      DateSerial(iYear, 1, ((iWeek - 1) * 7) + iWeekDday - Weekday(DateSerial(iYear, 1, 1)) + 1)

vDate = fnDateFromWeek
'vDate = DateAdd("yyyy", 0, "01/01/2009")

If Weekday(vDate, vbSunday) = 2 Then
        mon_date = vDate
      Else
        mon_date = vDate - Weekday(vDate, vbSunday) + 2
    End If

Select Case dag
    Case Is = 1
    dag = 0
    Case Is = 2
    dag = 1
    Case Is = 3
    dag = 2
    Case Is = 4
    dag = 3
    Case Is = 5
    dag = 4
    Case Is = 6
    dag = 5
    Case Is = 7
    dag = 6
End Select

daynumber1 = DateAdd("d", dag, mon_date)
daynumber = Format(daynumber1, "yyyymmdd")


End Function