Private Function Week(dteValue As Date) As Integer
   'Monday is set as first day of week
   Dim lngDate As Long
   Dim intWeek As Integer
   
   'If january 1. is later then thursday, january 1. is not in week 1
   If Not Weekday("01/01/" & Year(dteValue), vbMonday) > 4 Then
      intWeek = 1
   Else
      intWeek = 0
   End If
   'Sets long-value for january 1.
   lngDate = CLng(CDate("01/01/" & Year(dteValue)))
   
   'Finds the first monday of year
   lngDate = lngDate + (8 - Weekday("01/01/" & Year(dteValue), vbMonday))
   'Increases week by week until set date is passed
   While Not lngDate > CLng(CDate(dteValue))
      intWeek = intWeek + 1
      lngDate = lngDate + 7
   Wend
   'If the date set is not in week 1, this finds latest week previous year
   If intWeek = 0 Then
      intWeek = Week("31/12/" & Year(dteValue) - 1)
   End If
   Week = intWeek
End Function

msgbox "Сейчас идёт " & CStr(Week(Now)) & " неделя."