Abstract: A loan management system, which may be used to manage mortgages, includes a mortgage arrangement or “product” definition means for defining different data processing operations to be performed on different mortgages. Different sets of control data may be provided in, or linked to, the product definition means so as to control transactions relating to the product in a manner defined by the corresponding control data. In this way, transactions on different mortgages may be handled in different ways. Using the system it is possible to set up and manage many different kinds of offset—type mortgage arrangements in which the values of funds defined internally in the computer system may vary, for example in accordance with outside indices, and may be offset against outstanding capital and/or interest in a variety of different ways in different mortgages managed by the system.