We examined whether intrapersonal variability in the perception of partner’s behavior, perception spin, was related to partner’s intrapersonal variability in behavior, behavioral spin, and was associated with biases in the perception of negative affect. Ninety-three cohabiting couples reported their perceptions of partner’s affect and partner’s communal and agentic behavior in interactions with each other for 20 days. Perception spin was calculated as the within-person standard deviation of perception scores across interactions. Spin in the perception of the partner was associated with the partner’s behavioral spin. Participants with higher perception spin overestimated their partner’s negative affect and more strongly assumed that their partner’s affect was similar to their own negative affect. Thus, perception spin is an individual difference variable that reflects in part the extent of variability in the partner’s behavior, but higher spin also indicates distortions in perceptions of others.