This is a model of personal informatics systems that we hope would be valuable for research and development. It provides a common framework for describing, comparing, and evaluating the growing number of this class of systems. This model is composed of five stages (preparation, collection, integration, reflection, and action). These stages have four properties: barriers cascade to later stages; they are iterative; they are user-driven and/or system-driven; and they are uni-faceted or multi-faceted.