Month by week and year
Dim tDt As DateTime = New DateTime(year, 1, 1).AddDays(week * 7)
Dim tWeek As Integer = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(tDt, System.Globalization.CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday)
If week < tWeek Then
tDt = tDt.AddDays(-7)
End If