When and why does the experience of helping others at work spill over into positive affect at home? This paper presents a within-person examination of the association between perceived prosocial impact at work and positive affect at home, as well as the psychological mechanisms that mediate this relationship. Sixty-eight firefighters and rescue workers completed electronic diaries twice a day over the course of 1 working week. Random-coefficient modeling showed that perceived prosocial impact predicted positive affect at bedtime. This relationship was mediated by perceived competence at the end of the working day and positive work reflection during after-work hours but not by positive affect at the end of the working day. The findings demonstrate that the experience of helping others at work has delayed emotional benefits at home that appear to be channeled through the cognitive mechanisms of perceived competence and reflection rather than through an immediate affective boost.