Create Pivot Calculated Column in Excel 2016

[mrchonginhk]

I know how to do it in PowerPivot.
What if I do not have PowerPivot.
I need to create a new calculated column (not measure) in PivotTable simply like
[Margin] = [Sales]-[Cost]
I loaded the table into Data Model of Excel already (as I need to add measure later).
Where I add it ?

Thanks