Estimating the effort someone has spent on a task is a core dimension for evaluating own and other’s actions. Interestingly, it has been shown that self-judgments of effort are influenced by the magnitude of obtained rewards . However, it is unclear whether the influence of reward on effort estimations is limited to self-judgments (i.e. a form of self-serving bias) or whether reward information is invariably incorporated when judging effort, thus extending also to social contexts. Here we show that people also integrate reward magnitude when judging the effort exerted by another person. Participants (N=48, 24 pairs) performed an effortful task interleaved with a partner. In half of the trials, participants performed the task themselves and rated their own effort. In the other half, participants rated the other person’s effort after watching them performing the task. After each trial but before the effort rating, both participants were informed of the gained reward for that trial. Our results show that higher rewards led to higher estimations of exerted effort. Importantly, this was true for self- as well as other-judgments. In line with a Bayesian cue integration framework, reward magnitude had a stronger effect when judging the effort of another person, compared to self-judgments, since people should have more reliable internal estimates of own effort. Supporting this claim, computational modelling revealed that reward information and objective performance criteria related to the exertion level were combined in a Bayes optimal manner to form effort estimates. Interestingly, the extent to which rewards influenced effort judgments was positively correlated with conservative world-views, suggesting links between this effect and broader social attitudes.