Objectives: This study assessed accuracy and bias in people's perceptions of their romantic partner's adoption of short-term (avoid conflict) and long-term (later health) motives for interpersonally regulating their health behaviours.

Design: A cross-sectional Web-based survey of 114 cohabiting romantic couples (N = 228 individuals) living in the United States.

Methods: Romantic partners separately completed measures of their short-term and long-term motives for self-regulation and partner regulation of health behaviours, as well as their perceptions of partner regulation of their own health behaviours. Dyadic path analyses were conducted using the truth and bias model of judgement.

Results: Targets of interpersonal regulation perceived their romantic partner's short-term and long-term motives for influencing their (the target's) health behaviour with significant accuracy. However, targets' perceptions of their partner's motives simultaneously contained about the same amount of projection of the target's own short- and long-term motives for self-regulation. There was no similarity between the target's motives for self-regulation and their partner's motives for interpersonal regulation. Targets also tended to underestimate their partner's long-term motives for interpersonal regulation.

Conclusions: Although people are somewhat accurate in their perceptions of their romantic partner's motives for attempting to influence their health behaviours, their perceptions are also contaminated by biases. This suggests that people's judgements about their partner's motives could be substantially improved. Statement of contribution What is known about this subject? Romantic partners use social influence tactics to improve each other's health behaviours. People who perceive their partner's influence attempts positively often make healthy changes. Misperceptions of a partner's motives for influence attempts may have health and relationship implications. What does this study add? People are aware of whether partner influence attempts are motivated by convenience or concern. People also project their own motives for self-regulating health behaviours onto their partner.