Use this calculator to see how extra payments will affect your loan. This amortization calculator shows the schedule of paying extra principal on your mortgage over time.If you can use a spreadsheet, you can make your own mortgage calculator! Want to know the impact of "extra payments" on your mortgage? Check out this easy to use Excel mortgage calculator. If you want to pay off specific loans, select "Specify for Each Loan" and fill in the Current Balance amount for each loan you want to pay off. Extra Payment Calculator. Determine if extra payments to pay off your loan early is the right option for you. Click on Payments and then click on Request Payoff. The mortgage payoff calculator helps you find out.