Calculated Fields in a Pivot Table

I have percents (CTR and S/U %) in my pivot table that are currently totaling in the subtotal and total rows -- I need those to essentially calculate the net %...is there a way to set that up?

Also, very similar for the two CPM columns, instead of totaling I need to take "Sum of Cost" and divide that by "Sum of Impressions"/1000.

For UK, "Sum of Cost" would be: $92/ (72,634/1000)

Any help would be much appreciated!!

Anyone have any ideas??

Thank you!