Our affective states influence whether we help others and after helping we often experience improved affect or reduced stress. One important factor that determines whether we help, and the potential affective consequences of helping, is the amount of effort involved. People are usually less willing to help others if it involves significant effort. In this preregistered study, using an ecological momentary assessment approach in 527 participants, we investigated the affective antecedents and consequences of everyday helping in terms of individuals’ self-reported momentary stress and mood, with a specific focus on the perceived amount of effort involved in helping. Regardless of whether helping was deemed high or low in effort, greater energetic arousal predicted subsequent helping, which suggests we must be sufficiently energised when helping others. Contrary to our preregistered hypothesis, higher perceived stress predicted subsequent high effort, but not low effort, helping. Notably, whereas both low and high effort helping predicted subsequent greater energetic arousal, only low effort helping was associated with greater mood valence compared to not helping at all. Additionally, the greater the effort involved in helping, the greater the increase in stress after helping. Thus, the momentary affective benefits for the helper may be most pronounced when helping is associated with low effort costs. These findings have important implications for how the affective benefits of helping involving different amounts of effort can be used as part of a positive feedback loop that fosters and sustains prosocial behaviour.