Research on action-inaction regret has mostly examined morally-neutral, instrumental choices; far less is known about regret in prosocial contexts where help-offering is morally valued yet can be intrusive. We hypothesised that failing to meet recipients' expectations by offering unwanted help (action) would elicit more regret than not offering wanted help (inaction), particularly under weak prosocial norms. We manipulated (Study 1) or measured (Study 2) prosocial norms using workplace vignettes ( = 425). When norms discouraged helping, participants anticipated more regret following action, compared to inaction. However, when workplace norms encouraged helping, participants anticipated more regret following inaction. Moreover, participants expected actors to be less willing to help in the future than non-actors, especially under weak prosocial norms. These findings show that anticipated regret and behavioural intentions following prosocial action or inaction depend on social norms, suggesting that what people perceive as common behaviour shapes expected emotions and intentions in moral domains.