Release planning is a critical activity in the software development process. The creation of a clear and realistic plan is extremely difficult, as key factors such as time and cost to develop chosen functionality and the likely return are subject to a high level of uncertainty. As such the management decision as to which stories to develop and which to ignore can be an extremely difficult one requiring an expert balancing of competing benefits and risks. This paper proposes a relatively simple statistical methodology that allows for the uncertainty in story size, value and project velocity. In so doing it provides key stakeholders with the opportunity to manage uncertainty in the planning of future releases. The technique is lightweight in nature and consistent with existing agile planning practices.