Using current literature on the associations between breastfeeding and maternal and pediatric health, we modeled the costs of health outcomes for a US cohort of mothers and their infants born in 2002 and followed to age 70 years. Using Monte Carlo simulations, we modeled both pediatric and maternal disease using (a) current rates of breastfeeding (suboptimal) and (b) assuming that 90% of infants were breastfeed exclusively for 6 months, with continued breastfeeding for at least one year (optimal). The 9 pediatric conditions considered in this model were: acute lymphoblastic leukemia (ALL), acute otitis media (AOM), Crohn’s disease, ulcerative colitis, gastrointestinal infection (GII), hospitalization for lower respiratory tract infection (LRTI), obesity in non-Hispanic whites to age 4, necrotizing enterocolitis (NEC), and Sudden Infant Death Syndrome (SIDS). The 5 maternal conditions modeled were breast cancer, pre-menopausal ovarian cancer, type 2 diabetes mellitus, hypertension, and myocardial infarction. Total medical costs (e.g. direct medical costs and medical overhead), indirect societal costs, (e.g. time missed from work), and the cost of premature death were calculated for each condition. Premature death was defined as death at age 70 or earlier. All costs were calculated using US$ 2014 Dollars and a discount rate of 2%. For more about the model, including the assumptions used, please read our model appendix.