Subjective biology: how perceived fecundity influences relationship satisfaction and stability.

In high-income countries, fertility is increasingly postponed into ages when fecundity declines, elevating the risk of unmet reproductive goals. In this context, how individuals perceive their own and their partner's reproductive potential may carry important implications for well-being and relationship stability, long before clinical infertility is diagnosed. Drawing on 13 waves of longitudinal data from the German Family Panel (pairfam), this study uses individual fixed-effects models to examine how within-person changes in perceived fecundity - both one's own and one's partner's - are related to life satisfaction, relationship satisfaction, and union dissolution. By capturing both individual and partner assessments, this approach emphasizes the couple as the key unit of reproductive experience. Declines in both own and partner's perceived fecundity are associated with lower life and relationship satisfaction. However, perceptions of a partner's fecundity exert a stronger influence on relationship outcomes than self-perceptions. In particular, decreases in partner-perceived fecundity increase the risk of separation, a pattern not observed for changes in one's own fecundity. These associations do not vary significantly by gender but are moderated by parental status and age, with effects being weaker among parents and older individuals. By integrating both self- and partner assessments of fecundity, this study advances a dyadic, life course perspective on fertility. It shows that subjective reproductive potential functions as a relational stressor with meaningful consequences for emotional well-being and relationship trajectories.