This study explores the psychological, computational, and neural foundations of indebtedness, a complex emotional state that arises when someone receives a favor and feels obligated to reciprocate. The research combines a large-scale online questionnaire, an interpersonal game, computational modeling, and neuroimaging to develop and validate a conceptual model of indebtedness. The model identifies two distinct components of indebtedness: guilt, which arises from altruistic intentions and reflects communal concern, and obligation, which results from strategic intentions and is linked to social expectations and reputational costs. These components influence reciprocal behaviors, with guilt and gratitude motivating reciprocity out of concern for the benefactor, while obligation motivates reciprocity due to external pressures. The study shows that perceived altruistic intentions are associated with activity in the insula, ventromedial prefrontal cortex, and dorsolateral prefrontal cortex, while strategic intentions are linked to activation in the temporal parietal junction and dorsomedial prefrontal cortex. A neural utility model of indebtedness was developed using multivariate patterns of brain activity to predict reciprocity behavior. The model successfully captures the tradeoff between guilt and obligation and reliably predicts participants' trial-to-trial reciprocity behavior. The research also demonstrates that the processing of communal concern and obligation involves distinct neural mechanisms. Communal concern is associated with activity in the ventromedial prefrontal cortex and insula, while obligation is linked to the theory of mind network, including the dorsomedial prefrontal cortex and temporal parietal junction. These findings support the role of intention inference in the generation of these feelings and highlight the differential neural correlates of communal concern and obligation. The study provides a comprehensive understanding of the psychological, computational, and neural mechanisms underlying indebtedness and its impact on reciprocal behaviors.This study explores the psychological, computational, and neural foundations of indebtedness, a complex emotional state that arises when someone receives a favor and feels obligated to reciprocate. The research combines a large-scale online questionnaire, an interpersonal game, computational modeling, and neuroimaging to develop and validate a conceptual model of indebtedness. The model identifies two distinct components of indebtedness: guilt, which arises from altruistic intentions and reflects communal concern, and obligation, which results from strategic intentions and is linked to social expectations and reputational costs. These components influence reciprocal behaviors, with guilt and gratitude motivating reciprocity out of concern for the benefactor, while obligation motivates reciprocity due to external pressures. The study shows that perceived altruistic intentions are associated with activity in the insula, ventromedial prefrontal cortex, and dorsolateral prefrontal cortex, while strategic intentions are linked to activation in the temporal parietal junction and dorsomedial prefrontal cortex. A neural utility model of indebtedness was developed using multivariate patterns of brain activity to predict reciprocity behavior. The model successfully captures the tradeoff between guilt and obligation and reliably predicts participants' trial-to-trial reciprocity behavior. The research also demonstrates that the processing of communal concern and obligation involves distinct neural mechanisms. Communal concern is associated with activity in the ventromedial prefrontal cortex and insula, while obligation is linked to the theory of mind network, including the dorsomedial prefrontal cortex and temporal parietal junction. These findings support the role of intention inference in the generation of these feelings and highlight the differential neural correlates of communal concern and obligation. The study provides a comprehensive understanding of the psychological, computational, and neural mechanisms underlying indebtedness and its impact on reciprocal behaviors.