There is not a report that will specifically give a percentage. You can, however, use either the Insurance Carrier Report or a run a Patient Report (by filters) to get a total number of patients on an insurance plan and then divide this by the total number of patients to get the percentage.
(Patients on insurance / Total number of patients) x100 = Percent of patients on the insurance.
For example, if the report had 500 patients on Delta Dental and there are a total of 10,000 patients in the database, then:
0.05 x 100 = 5
So 5% of the patients are on Delta Dental.