where f total finance charge n x m p
m regular monthly loan paymentp original loan amountk remaining number of loan payments after current paymentn original number of paymentsfor example a borrower takes a 10 000 loan on a car to be repaid in 48 monthly installments of 310 00 however she repays the loan after 36 months the lender s unearned interest can be calculated to be f 48 x 310 10 000f 4 880unearned interest 4 880 x 12 x 13 48 x 49 unearned interest 4 880 x 156 2352 unearned interest 4 880 x 0 0663unearned interest 323 67