The mortgage payment calculator uses the amount of your mortgage, how often you make the mortgage payments, and the interest rate that you’re getting from your lender in order to figure how much your mortgage payments will be. As with all of the calculators on Which Mortgage, you can play around with the numbers in order to see how the differences in these variables all affect your bottom line. You can also see the breakdown of how much you’re paying in interest for each of the resulting payment options.