The present study explores public pension claiming behaviour among the Japanese elderly. First, we perform financial simulations, estimate expected utility and depict the typical patterns of pension benefits over a lifecycle. We show that a beneficiary's optimal retirement age depends on that beneficiary's mortality risk, discount rate, initial wealth and risk attitude. Second, we use individual‐level data from the Japanese Study on Aging and Retirement (JSTAR) to empirically examine the determinants of claim timing. We find evidence that most of the factors examined in the simulation are, indeed, significantly associated with early claiming among wage earners of pension benefits.