Loneliness is linked to reduced calibration of confidence to uncertainty in social decision-making.

Loneliness is associated with altered social cognition and decision-making, yet the processes through which it shapes behavior in uncertain social contexts remain poorly understood. In particular, little is known about how loneliness relates to metacognitive evaluations of decision reliability. The present study examined whether loneliness is associated with differences in decision confidence and its calibration to uncertainty during social decision-making. Data were collected from two independent general population samples (N = 6,517) using a vignette-based task in which participants decided to engage in or avoid social interactions and rated their confidence. Across both samples, higher loneliness was associated with lower overall decision confidence. Critically, loneliness moderated the relationship between decision difficulty and confidence such that individuals reporting higher loneliness showed reduced sensitivity of confidence to increasing difficulty, indicating diminished calibration to uncertainty across diverse social decision contexts. In contrast, loneliness was not associated with differential confidence between engagement and avoidance decisions. These findings were robust after adjusting for demographic variables and symptoms of depression and anxiety. The results suggest that loneliness is linked to altered metacognitive evaluation rather than biases in decision outcomes, highlighting impaired confidence calibration as a potential mechanism underlying persistent loneliness and maladaptive social functioning.