An agreement with your bank to spend more money than you actually have in your account. As you are borrowing money from the bank, there can be a charge for this service. You must be 18 years or over to have an overdraft. An agreed overdraft is the limit up to which the account holder may borrow from the bank, when there are no funds in his or her current account. To minimise excess bank charges it is important that you do not exceed the limit that has been agreed with the bank.