Hi vonsworld,

See if this works for you. You need to make a string from those numbers. I've used CStr() but then how many "0" to add..
Sub StrCtr()
    Dim NumCtr As Double
    Dim StrCtr As String

    For NumCtr = 1 To 12
        If Len(CStr(NumCtr)) = 1 Then
            StrCtr = "00" & CStr(NumCtr)
        Else
            StrCtr = "0" & CStr(NumCtr)
        End If
        
        Set WBS = Workbooks.Open("D:\Spending" & StrCtr & ".xlsx")
        ' Your Code

    Next NumCtr

End Sub