Sub test4()
Dim LastLig As Long, i As Long
Dim Tb
Application.ScreenUpdating = False
With Worksheets(1)
LastLig = .Cells(.Rows.Count, 1).End(xlUp).Row
Tb = .Range("AC1:AF" & LastLig)
For i = 2 To LastLig
Tb(i, 1) = Val(Tb(i, 4)) - Val(Tb(i, 3)) + 1
Next i
.Range("AC1:AF" & LastLig) = Tb
End With
End Sub