Greetings. Click anywhere on Pivot Table. On Pivot Table toolbar find "Pivottable" (with a tiny arrow pointing down next to it) - choose "Formulas" - choose "Calculated Field.."
Where it says "Add" type in a header name of your choice. Using the fields available insert
"Sum Due Service" / "Count of Patients" then click the button "Add"
Ok your way out.. (you may have to format the cells to percentage)
Hope this helps.