To illustrate why bond prices and market interest rates tend to move in opposite directions, suppose you purchased a 5-year, $1,000 bond at face value that was paying a 7% coupon rate. Now, suppose market interest rates rise, thereby causing bonds similar to yours to offer, say, an 8% coupon rate. If you were looking to sell your 7% bond, you Calculator Rates Loan Comparison Calculator. This calculator will calculate the monthly payment and interest costs for up to 3 loans -- all on one screen -- for comparison purposes. To calculate the payment amount and the total interest of any fixed term loan, simply fill in the 3 left-hand cells of the first row and then click on "Compute."