The process of planning to teach mathematics is complex and idiosyncratic and is gaining increased attention in educational research. In this paper, I propose a framework for conceptualising the critical factors that influence teachers' mathematics planning decisions. The framework is informed by the analysis of teacher survey data (n=114) and two case studies, a Year 1 (n=5) and Year 5 (n=4) teaching team. In this paper I illustrate the way the framework enhanced the analysis and discussion of the Year 5 case study. The potential of the framework to drive future research and teacher professional learning is discussed.