Previous research has shown that anorexia nervosa (AN) and bulimia nervosa (BN) are expensive illnesses to treat. To reduce their economic burden, adequate interventions need to be established. Our objective was to conduct cost-offset analyses for evidence-based treatment of eating disorders using outcome data from a psychotherapy trial involving cognitive behavioral therapy (CBT) and focal psychodynamic therapy (FPT) for AN and a trial involving CBT for BN. Assuming a currently running, ideal healthcare system using a 12-month, prevalence-based approach and varying the willingness to participate in treatment, we investigated whether the potential financial benefits of AN-and BN-related treatment outweigh the therapy costs at the population level. We elaborated on a formula that allows calculating cost-benefit relationships whereby the calculation of the parameters is based on estimates from data of health institutions within the German healthcare system. Additional intangible benefits were calculated with the aid of Quality-Adjusted Life Years. The annual costs of an untreated eating disorder were 2.38 billion EUR for AN and 617.69 million EUR for BN. Independent of the willingness to participate in treatment, the cost-benefit relationships for the treatment remained constant at 2.51 (CBT) and 2.33 (FPT) for AN and 4.05 (CBT) for BN. This consistency implies that for each EUR invested in the treatment, between 2.33 and 4.05 EUR could be saved each year. Our findings suggest that the implementation of evidence-based psychotherapy treatments for AN and BN may achieve substantial cost savings at the population level.