A line of credit optimized for a retailer and attached to a customer account at a financial institution is established for a customer of the retailer. A financial institution computer determines whether to advance funds through the line of credit for a transaction, then advances funds in one or more preselected loan increments to the customer account, up to a total available line of credit for the customer. The financial institution computer decrements the total available line of credit by the amount provided for the customer transaction and by a predetermined customer fee for each of the loan increments. The computer determines a value of a retailer fee to be paid by the retailer, involving a predetermined amount for each of the loan increments. The customer fee amount can be zero or discounted for customer transactions with the retailer. The retailer fee can be a rebate to the customer.