- Navigate to Reports > Sales > Sales by Customer > Customise Summary.
- On the Report Builder > Expand the Sales folder and add in the Est. Extended Cost (Line).
- Add Formula Field:
Percent Difference of X ((x-y)/x)*100
y=Est. Extended Cost (Line)
- Click on Preview.
- Set Date = Custom > From Jan. 1, 2013 To Dec. 31, 2013
- Set Column = Month.
- Click on Refresh.
Result: Formula column is not showing as part of the columns per month but only showed once.
Customize the report again > highlight the Formula column and make sure to mark the Add Grand Total check box. The formula column should now appear per month.