Background <p>How accurate are empathic judgments of couples in smartphone messenger communication? Are judgments influenced by the level of experience with messengers and communication frequency?.</p> Objectives <p>The current preregistered study introduced a novel ecological assessment method and a privacy by design approach to study couples’ empathic accuracy in a messenger context.</p> Methods <p>Data from <i>N</i> = 102 participants (51 couples) was used to investigate how accurate judgments of partners’ affect map their partners’ actual affect.</p> Results <p>Our results demonstrate tracking accuracy and assumed similarity bias in reciprocal empathic judgments of affective valence and arousal during social messenger texting. A small moderation effect for experience with text messengers was found, indicating that partners with higher experience have a higher bias of assumed similarity when rating their partner’s valence. A small moderation effect for communication frequency confirms that higher messenger communication frequency is associated with more accurate judgments of arousal.</p> Conclusion <p>These results point to the reciprocal action of accuracy and bias in couples’ messenger communication and the distinct influences of experience and usage. The feasibility and further application of the ecological messenger-based assessment of couples’ empathic accuracy in interpersonal research are discussed.</p>