Although planning is a crucial part of the system development process, it is often neglected by project managers. The problem being addressed by this paper is that of inadequate models for planning the requirements capture and analysis stage (RCA) of a software development project. It is stressed that there is a need for a new model because the existing models give inaccurate, inconsistent or unreliable predictions. Additionally, they are based on either inappropriate variables or variables that can not be measured at the beginning of the development process. Finally, existing models do not support the planning of individual stages of the development process but only try to make predictions about the project development process as a whole. This paper examines existing models and provides evidence about their inadequacy and lack of accuracy, and then introduces a new model and presents the approach followed for its development.