The motivation to feel moral powerfully guides people’s prosocial behavior. We propose that people’s efforts to preserve their moral self-regard conform to a moral threshold model. This model predicts that people are primarily concerned with whether their prosocial behavior legitimates the claim that they have acted morally, a claim that often diverges from whether their behavior is in the best interests of the recipient. Specifically, it predicts that for people to feel moral following a prosocial decision, that decision need not have promised the greatest benefit for the recipient but only one larger than at least one other available outcome. Moreover, this model predicts that once people produce a benefit that exceeds this threshold, their moral self-regard is relatively insensitive to the magnitude of benefit that they produce. In six studies, we test this moral threshold model by examining people’s prosocial risk decisions. We find that, compared with risky egoistic decisions, people systematically avoid making risky prosocial decisions that carry the possibility of producing the worst possible outcome in a choice set—even when this means avoiding a decision that is objectively superior. We further find that this aversion to producing the worst possible prosocial outcome leads people’s prosocial (vs. egoistic) risk decisions to be less sensitive to those decisions’ maximum possible benefit. We highlight theoretical and practical implications of these findings, including the detrimental consequence that people’s desire to protect their moral self-regard can have on the amount of good that they produce.