Planning and replanning software projects involves selecting activities according to organisational policies, project goals and contexts, deciding how to effect the activities, and dealing with uncertainty in activity outputs. There is at the present time no general model to support project managers with all of these tasks. The contributions of this paper are to propose a set of properties that are desirable in a model for (re)planning and to create a framework based on these properties. The purpose of the framework is to support the modelling and simulation of (re)planning during software projects. Key aspects of the framework are a focus on project objectives as drivers of activity selection, and activity prediction that supports uncertainty and that may be based on previous activity data, expert opinion or experimental evidence. We present a `proof-of-concept' case study to illustrate how the framework can be applied to support planning.