All prepayments shall first be applied to outstanding late fees, then to accrued interest and thereafter to the principal loan amount. Download a Free Balloon Loan Payment Calculator for Excel.Calculate the balloon payment and amortization schedule for variaous loans. This amortization calculator returns monthly payment amounts as well as displays a schedule, graph, and pie chart breakdown of an amortized loan. Set loan terms with larger payments at the end. This spreadsheet creates an amortization schedule for a fixed-rate loan, with optional extra payments. Here are the steps you can follow to calculate balloon payments using promissory notes: 1. Determine the amount of the loan.