Amortization Schedule with Extra Payments Amortization schedules can be extremely helpful in understanding how your loans work. They break out each payment one by one and list how much interest you pay each month. Amortization schedules can be a useful tool in analyzing your debt so you can get rid of it. Description. Calculate the difference in total interest paid on a mortgage loan when making additional monthly payments.. Since creating this spreadsheet, I've created many other calculators that let you include extra mortgage payments.The most advanced and flexible one is my Home Mortgage Calculator. * For Excel 2003: The CUMIPMT function requires the Analysis ToolPak, which comes with Excel An amortization schedule shows the interest applied to a fixed interest loan and how the principal is reduced by payments. It also shows the detailed schedule of all payments so you can see how much is going toward principal and how much is being paid toward interest charges.