The structure of the Social Security program presents a trade-off between benefit duration and size; individuals who claim early receive lower monthly payments. Surprisingly, even wealthy Americans with high life expectancies frequently claim benefits at the earliest eligibility age, a behavior inconsistent with conventional life-cycle theory predictions. In fact, there is a striking similarity in claiming ages across groups with vastly different life expectancies, wealth levels, and incentives to delay. This paper resolves this puzzle by introducing policy details and subjective beliefs about longevity and program rules into a rich, forward-looking life-cycle model. When included in the model, subjective beliefs substantially narrow the claiming-age gaps across education (college vs. non-college) and marital-status (married vs. single) groups. Specifically, differences in program beliefs alone account for 48.6% of the education claiming age gap and 75.1% of the marital status gap. Counterfactual policy simulations demonstrate that failing to account for these claiming mechanisms dramatically overstates individual responses to an increase in the normal retirement age and understates the resulting fiscal savings.