Zonder deftig voorbeeld maak ik er dit van:
Sub dotchie()
If [G2].Value = "" Then
[A1].FormulaR1C1 = _
"=INT((R[2]C[6]-(DATE(YEAR(R[2]C[2]+(MOD(8-WEEKDAY(R[2]C[2]),7)-3)),1,1))-3+MOD(WEEKDAY(DATE(YEAR(R[2]C[2]+(MOD(8-WEEKDAY(R[2]C[2]),7)-3)),1,1))+1,7))/7)+1"
Else
[A1].FormulaR1C1 = _
"=INT((R[2]C[9]-(DATE(YEAR(R[2]C[8]+(MOD(8-WEEKDAY(R[2]C[8]),7)-3)),1,1))-3+MOD(WEEKDAY(DATE(YEAR(R[2]C[8]+(MOD(8-WEEKDAY(R[2]C[8]),7)-3)),1,1))+1,7))/7)+1"
End If
End Sub