You may be able overpay a certain amount each month. This will allow you to pay the mortgage early and therefore would have also paid less interest. In addition to this, if you have made over payments they may also allow you to withdraw these later. For example say you over paid for 6 months by £50. Then in the 7th month you wish to take all of your overpayments back. As you have over paid by £300 (6 months at £50) which will mean you can take back £300 from your mortgage. This varies from mortgage to mortgage so you will have to read their terms and conditions before signing up with them.