We report results from an on-line economics experiment that examines the effect of nudging retirement savings decisions. In the experiments, participants make decisions in a finitely repeated retirement savings game, in which income during working years is uncertain, and retire-ment age is known. Participants, who are household financial decision-makers, are nudged with automatic savings in each period of the game. We find that that the nudge simply replaced nat-ural decision-making observed in the absence of a nudge in this experiment, even to the extent that it resulted in nearly identical inferred decision rules. This surprising result highlights the unpredictability of the effect of nudging human behavior.