Imagining helping others increases prosocial intentions and behavior toward those individuals. But is this true for everyone? We used an imagined helping paradigm and a battery of prosocial measures to determine whether the prosocial benefits of imagination depend upon an individual’s general tendency to help others. We found that the effects of imagination on prosociality were larger for less altruistic individuals. We didn’t find a link between the efficacy of episodic imagination and people’s tendency to enforce social norms or to describe themselves as prosocial. These results suggest leveraging people’s abilities for episodic simulation as a promising strategy for increasing prosociality, particularly for those least likely to help otherwise.