Current Prime Rate Us Interest Rate Vs Apr Calculator How to Calculate APR vs. Interest Rate on a Loan – LendGenius – APR and interest rate are more closely related than either is with factor rate, so we’ll discuss those two first before describing how a factor rate might come into play. What is an APR vs. interest rate? The interest rate is the annual cost of a loan to a borrower expressed as a percentage of the principal loan amount. easy enough so far.