Incremental software development, the staged delivery of products, offers many benefits compared with more traditional development approaches. Indeed, incremental approaches have been utilized for many years due to the involvement of users, early demonstration of capability, and potential for risk reduction that they offer. However, there appears to have been little work on modeling, planning and controlling incremental development. This paper attempts to introduce a quantitative analytical framework for evaluating such approaches and their economic impacts. The use of a Constructive Cost Model (COCOMO)-style effort framework developed in this paper explores some of the relationships between effort and the number of increments, thereby providing new insights into the economic impact of incremental approaches to software projects.