Receipt of reward leads to altered estimation of effort.

Effort and reward jointly shape many human decisions. Errors in predicting the required effort needed for a task can lead to suboptimal behavior. Here, we show that effort estimations can be biased when retrospectively reestimated following receipt of a rewarding outcome. These biases depend on the contingency between reward and task difficulty and are stronger for highly contingent rewards. Strikingly, the observed pattern accords with predictions from Bayesian cue integration, indicating humans deploy an adaptive and rational strategy to deal with inconsistencies between the efforts they expend and the ensuing rewards.