Empathy theoretically serves an affiliative interpersonal function by satisfying motives for intimacy and union with others. Accordingly, empathy is expected to vary depending on the situation. Inconsistent empirical support for empathy's affiliative role may be because of methodology focused on individual differences in empathy or differences between controlled experimental conditions, which fail to capture its dynamic and interpersonal nature. To address these shortcomings, we used ecological momentary assessment to establish typical patterns of empathy across everyday interactions. Associations among empathy, affect, and interpersonal behaviour of self and interaction partner were examined in a student sample (N = 330), then replicated in a preregistered community sample (N = 279). Multilevel structural equation modelling was used to distinguish individual differences in empathy from interaction-level effects. Results show that people are more empathetic during positively valenced interactions with others perceived as warm and when expressing warmth. By confirming the typically affiliative role of empathy, existing research to the contrary can be best understood as exceptions to the norm.