Prior work suggests that imagining helping others increases prosocial intentions and behavior toward those individuals. But is this true for everyone, or only for those who tend toward--or away from--helping more generally? The current study (N = 283) used an imagined helping paradigm and a battery of behavioral and self-report measures of trait prosociality to determine whether the prosocial benefits of imagination depend upon an individual's general tendency to help others. Replicating prior work, we found links between imagination and prosociality and support for a three-factor model of prosociality comprising altruistically, norm-motivated, and self-reported prosocial behaviors. Centrally, the effects of imagination on prosociality were slightly larger for less altruistic individuals but independent of norm-motivated and self-reported prosociality. These results suggest leveraging people's abilities for episodic simulation as a promising strategy for increasing prosociality in general, and perhaps particularly for those least likely to help otherwise.