How do you determine what rate to charge me? You are charged premiums using base rates for each of your risk classifications. These premiums include rates for each of the four different premiums you are required to pay: Accident fund premiums, medical aid fund premiums, stay-at-work program premiums, and supplemental pension fund premiums. Your premiums for each classification are determined by multiplying your experience factor by the sum of the accident fund, medical aid fund and stay-at-work program base rates for that class, and then adding the supplemental pension fund rate.