Some mortgage calculators let you add an estimated early repayment charge (ERC), but they cannot confirm the exact amount you may owe. Your lender usually calculates the ERC using your outstanding balance, the charge percentage and how long remains on your deal, subject to the terms of your mortgage. Check your mortgage offer or contact the lender for a current redemption figure, including any fee-free overpayment allowance. If you are considering switching, a regulated mortgage adviser can help compare the costs.