Monthly Payment Calculator (7ci) Adjustable Rate Mortgages With Flexible Payment Options Who This Calculator is For: Borrowers who want to know how the interest rate and monthly payments may change on a monthly adjustable rate mortgage that permits negative amortization if they select alternative payment options. What This Calculator Does: This calculator displays amortization schedules on a monthly adjustable rate mortgage that permits negative amortization, on four different assumptions regarding the payment option selected by the borrower.