Individuals with anxiety and depression exhibit chronic metacognitive biases such as underconfidence. The origin of such biases is unknown. Here we quantified the impact of feedback valence on confidence in two large general population samples (N=230 and N=278). We studied metacognition both locally, as confidence in individual task instances, and globally, as longer run self-performance estimates. Global confidence was sensitive to both local confidence and feedback valence – more frequent positive (negative) feedback increased (respectively decreased) global confidence. Feedback valence impacted confidence in a domain-general fashion and also led to shifts in affective self-beliefs. Notably, global confidence was more sensitive to low (vs. high) local confidence in individuals with greater transdiagnostic anxious-depression symptomatology, despite sensitivity to feedback valence remaining intact. Together, our results reveal a mechanistic basis for chronic underconfidence in anxious-depression rooted in distorted interactions between local and global metacognition, while also highlighting potential for restoring confidence through targeted feedback.