In this paper, we consider the problem of accelerating commercial product development by overlapping adjacent functions. We formulate an approach, called iterative overlapping, in which downstream development activities start with preliminary design information and incorporate upstream design changes in subsequent iterations. In the absence of careful control, iterative overlapping could cause excessive downstream rework and result in an increase in development time. We develop models of iterations and design change to help decide when upstream design information should be committed for downstream iterations. When applied to an automobile door panel development process at a US automaker, the models suggest improvements that would reduce development time by 27%.