Pivot Table - Calculated Field

Hi,

I have an excel list with 2 column ( ID and OT). OT column can have only two values either "Late" or "On Time".
I create a pivot table based on this data.


Please see the attached sheet...

I want to use "Grand Total" and "On Time" column in calculation and I want the result to be inside pivot table.

At present I am manually calculating it outside the pivot.