This calculator computes the payment amount necessary for a mortgage with a balloon payment, using monthly interest compounding and monthly payments. A balloon payment is a large payment due at the end of a mortgage.A balloon mortgage will have monthly installments that are charged at a fixed interest rate. Learn everything you need to know about balloon notes in mortgage loans. Find out how they work and how they can affect your finances. What is a Balloon Payment? A balloon payment is when you have to make a one-time payment on your loan before the maturity date.