What's the total interest you pay on a loan? Take the total of payments, subtract the principal. e.g. 8% annual rate, 24 months, 10000 principal, no balloon payment or balance left, pay at end. annual rate 8% months 24 present value 10,000 future value (balloon payment) 0 pay at end of period What would the payment be if you were to pay at the beginning of the period? 452.27 452.27