Delaying rewards reduces egoism bias during prosocial acts.

People tend to prioritize their own benefits over those of others during reward evaluation, a tendency known as egoism bias. Recent evidence suggests that delaying rewards may reduce this bias in prosocial behavior, yet the underlying mechanisms remain unclear. This study investigated this issue by recording EEG activity when participants (N = 40) evaluated immediate or delayed rewards for themselves and an anonymous person during a prosocial reward task. We found an egoism bias in immediate reward evaluation, with stronger preferences and neural reward sensitivity (as indexed by the reward positivity, P3, and delta power) for self-benefiting compared to other-benefiting trials. Crucially, this egoism bias decreases when rewards were delayed, as shown by comparable reward sensitivity, overlapping neural representations, and positive neural correlations between self-benefiting and other-benefiting trials. These convergent findings establish reward deferral as a critical variable in reducing egoism bias during prosocial decision-making.