Public Function WeekOfYear(ByVal d As Date) As Integer
        Return DateDiff(DateInterval.WeekOfYear, CDate("1 Jan " & d.Year.ToString), d) + 1
End Function

 

Public Function StartDateOfWeekOfYear(ByVal weekOfYear As Integer, ByVal Year As Integer) As Date
        If weekOfYear < 1 OrElse weekOfYear > 53 Then
            Throw New ApplicationException("Invalid Week Of Year")
        End If
        Dim d As Date = CDate("1 Jan " & Year.ToString)
        If weekOfYear = 1 Then
            Return d
        Else
            Return d.AddDays(((weekOfYear - 1) * 7) - d.DayOfWeek)
        End If

 End Function