The optimal adjuvant therapy (antiestrogen therapy [ET] + radiation therapy or ET alone, or in some reports radiation therapy alone) in older women with early-stage breast cancer has been highly debated. However, granular details on the role of insurance in the out-of-pocket cost for patients receiving ET with or without radiation therapy are lacking. This project disaggregates out-of-pocket costs by insurance plans to increase treatment cost transparency. Several radiation therapy schedules are accepted standards as per the National Comprehensive Cancer Network guidelines. For our financial estimate model, we used the 5-fraction and 15-fraction radiation therapy and ET prescribed over a 5-year duration. The total aggregate out-of-pocket costs were determined from the sum of treatment costs, deductibles, and copays/coinsurance based on Medicaid, Original Medicare, Medigap Plan G, and Medicare Part D Rx plans. The model assumes a Medicare- and/or Medicaid-eligible patient ≥70 years of age with node-negative, early-stage estrogen-receptor-positive breast cancer. Patient out-of-pocket costs were estimated from publicly available insurance data from plan-specific benefit coverage materials using a 5-year time horizon. Original Medicare beneficiaries face a total out-of-pocket treatment charge of $2738.52 for ET alone, $2221.26 for 5-fraction radiation therapy alone, $2573.92 for 15-fraction radiation therapy alone, $3361.26 for combined ET+ 5-fraction radiation therapy, and $3713.92 for combined ET + 15-fraction radiation therapy. Medigap Plan G beneficiaries have an out-of-pocket charge of $1130.00 with radiation therapy alone and face an out-of-pocket of $2270.00 for ET alone and combined ET+ radiation therapy. For Medicaid beneficiaries, all treatments approved by Medicaid are covered without limit, resulting in no out-of-pocket expense for either adjuvant treatment option. This model (based on actual cost estimates per insurance plan rather than claims data), by estimating expenses within Medicare and Medicaid plans, provides a level of transparency to patient cost. With knowledge of the costs borne by patients themselves, treatment decisions informed by patients' individual priorities and preferences may be further enhanced.