Public Sub SumDemo()
    Dim ColSumRng As Range, hdr As Variant
    Dim FirstEmptyRow As Long, SubTot As Long

    ' Goto each column header starting with column B
    For Each hdr In Range("A1:L1").SpecialCells(xlCellTypeConstants, 3)

        ' Find where data ends for the specific Column
        FirstEmptyRow = Cells(65536, hdr.Column).End(xlUp).Row + 1

        ' Subtotal all numbers for Column
        SubTot = Application.WorksheetFunction.Subtotal(9, Range(hdr.EntireColumn.Address))

        ' Put Subtotal at bottom of column
        Cells(FirstEmptyRow, hdr.Column).Value = SubTot

    Next hdr
End Sub