Beliefs about future events are crucial to the decisions that people make when developing financial plans over the life cycle. Yet peoples’ subjective beliefs can often differ from the objective probabilities that economists and financial planners use in their models. This chapter discusses findings on subjective beliefs, how people might form their beliefs, and how these beliefs affect conclusions drawn from a classical economic life cycle model. I highlight a specific divergence between subjective beliefs and objective probabilities: subjective beliefs about peoples’ mortality.