Here's how it works: You input your original mortgage balance, the original term and interest rate. Then figure out how many month's of payments you've already made. Finally, decide how soon you'd like to have your mortgage paid off. For example, a couple in their 40's may decide that they'd like to pay off the 30-year loan they took out last year in 20 years. They input the particulars of their current loan, put in a new term of 20 years, and the Early Payoff Calculator determines how much extra they need to pay each month to make that happen.