You pay almost all interest in the first few years otherwise. It's the same as minimum payments on credit cards.Want to make an overpayment and understand how this could impact your mortgage payments and interest? Pop your details into our simple overpayment calculator. To obtain an overpayment refund, complete and sign the Application for Tax Refund. Reminder: To claim a tax credit (with the exception of the household credit and NYC school tax credit) you must complete and attach the appropriate credit form. Overpay is misleading. You can pay your mortgage and if given the option, pay additional funds directly toward the principle. Credit card payments any time up to the due date.