Here's the information you'll need to have handy to complete your unsecured promissory note, interest-only with balloon final payment. Here's the information you'll need to have handy to complete your secured promissory note, interest-only with balloon final payment.A balloon mortgage is usually rather short, with a term of five to seven years, but the payment is based on a term of 30 years. A single final balloon payment for the entire outstanding Principal amount and interest accrued will be paid on or before the day of. Or, you can use the interestonly formula to calculate the monthly payment for a balloon loan or interestonly mortgage. Payments shall be applied first to costs of collection, then to interest, then to principal. A monthly interest rate can be included on the promissory note. A promissory note or bond must always accompany the mortgage.