Early repayment charges are penalties for going over the mortgage overpayment threshold and are usually between 1% and 5% of the amount you overpaid. The percentage tends to go down the further into the deal you get. If, for example, you want to pay off a £100,000 mortgage in full within the discounted period, you could be asked to pay up to £5,000 in early repayment fees. Most lenders will however allow you to overpay by a certain amount per year - say up to 10% of the total amount owed - without incurring early repayment charges.