The prevalence of cancer survivorship is increasing. In this study, we provide contemporary population-based estimates and projections of the overall and site-specific cancer-attributable medical care costs in the United States. We identified survivors aged ≥65 years diagnosed with cancer between 2000 and 2012 from the Surveillance, Epidemiology, and End Results (SEER)-Medicare database and used 2007 to 2013 claims to estimate costs by cancer site, phases of care, and stage at diagnosis. Annualized average cancer-attributable costs for medical care (Medicare Parts A and B) and oral prescription drugs (Medicare Part D) were estimated by subtracting costs between patients with cancer and matched controls. Costs are reported in 2019 U.S. dollars. We combined phase-specific attributable costs with prevalence projections to estimate national costs from 2015 through 2030. Overall annualized average costs were highest in the end-of-life-cancer death phase, followed by the initial and continuing phases (medical care: $105,500, $41,800, and $5,300 and oral prescription drugs: $4,200, $1,800, $1,100, respectively). There was considerable variation in costs by cancer site and stage. Overall national costs in 2015 were $183 billion and projected to increase 34% to $246 billion by 2030, based only on population growth. Phase of care cancer-attributable cost estimates by cancer site and stage are key inputs for simulation models and cost-effectiveness analyses. The national cancer-attributed medical care costs in the United States are substantial and projected to increase dramatically by 2030, due to population changes alone, reflecting the rising burden of cancer care among cancer survivors.