geekgirlau, could you show me how to implement this code ?
Would be be great if I got this going... !
I am not to experienced with writing code..

I did this but getting errormessage :3001 invalid argument where the pointer is set to : Set rec =

Private Sub Kapitaal_AfterUpdate()
Dim strProvisie As Variant
Dim Prov As Variant
Dim strKap As Variant
strKap = Me.Kapitaal.Value
Sql = "SELECT Verzekering.v_ID, Verzekering.maatschappij, Verzekering.soort," _
& "Verzekering.ProvisiePerc, Polissen.VerzId," _
& "([Polissen].[Kapitaal]*[Verzekering].[ProvisiePerc]) AS Prov" _
& "FROM Verzekering INNER JOIN Polissen ON Verzekering.v_ID = Polissen.VerzId;"
 
Set rec = CurrentDb.OpenRecordset(Sql, dbOpenSnapShot)
 
If Not rec.EOF Then
    MsgBox Prov, vbOKCancel, "testing"
End If
If Me.VerzId = 1 Then
    Me.Provisie = strKap * strProvPerc
    'ElseIf Me.VerzId = 2 Then
    'Me.Provisie = Me.Kapitaal * (Prov)
 'ElseIf Me.VerzId = 4 Then
 '   Me.Provisie = Me.Kapitaal * (Prov)
  Else: Me.Provisie = 0
 
  MsgBox stProv, vbOKCancel, "Provisie Berekening"
End If
End Sub