Medicare is a federal health insurance program in the United States that provides coverage primarily to individuals aged 65 and older, as well as to certain younger people with disabilities or end-stage renal disease. Administered by the Centers for Medicare & Medicaid Services (CMS), it is one of the largest public insurance programs in the world by enrollment and expenditure. How Medicare should be structured, funded, and expanded is a subject of ongoing political and policy debate; the program's appropriate scope and relationship to private insurance markets are themselves contested questions linked throughout this article.

Medicare is organized into four main parts. Part A covers inpatient hospital care, skilled nursing facility stays, hospice, and some home health services, and is funded primarily through payroll taxes. Part B covers outpatient services, physician visits, preventive care, and durable medical equipment, funded through premiums and general revenue. Part C, known as Medicare Advantage, allows beneficiaries to receive their Medicare benefits through approved private insurance plans. Part D, added in 2003, covers prescription drugs through private plans subsidized by the federal government.

As of the mid-2020s, Medicare covers approximately 65 million Americans. Program spending represents a substantial share of the federal budget and of overall U.S. health expenditures. The Medicare Hospital Insurance Trust Fund, which finances Part A, has faced projected shortfalls in its long-term actuarial estimates, though the timing and severity of those projections have shifted across successive annual reports from the CMS Office of the Actuary.

Medicare interacts with several adjacent policy areas, including the Affordable Care Act, Social Security, Medicaid, and broader debates over the U.S. health care system. The program's reimbursement rates influence provider behavior and hospital economics across the health sector. Ongoing legislative and regulatory activity continues to reshape program details, including drug pricing negotiation authority granted under the Inflation Reduction Act of 2022.

There is broad agreement among health economists and policy researchers across institutions that Medicare significantly reduces rates of uninsurance among the elderly population. There is also substantial evidence that Medicare enrollment at age 65 is associated with improved access to care and reduced out-of-pocket spending for beneficiaries. See medicare-consensus-coverage-effects-consensus.

Research consistently documents that Medicare's administrative costs, as a share of expenditure, are lower than those of most private insurers, though the magnitude of this difference is subject to methodological debate over how administrative costs are measured across public and private programs. See medicare-consensus-administrative-efficiency-consensus.

Medicare as a successful public program - Proponents of this view hold that Medicare demonstrates the capacity of government-administered insurance to deliver broad, efficient coverage and argue the program should be expanded, potentially to all age groups. See medicare-expansion-supportive-viewpoint.

Medicare as fiscally unsustainable - Some economists, fiscal policy analysts, and conservative commentators argue that Medicare's long-term obligations represent an unsustainable claim on federal revenues and that structural reforms - including means-testing, premium support, or raising the eligibility age - are necessary. See medicare-fiscal-sustainability-viewpoint.

Medicare Advantage as privatization - Critics of Part C contend that Medicare Advantage plans introduce profit extraction, coverage restrictions, and administrative complexity into a program that functioned more equitably without private intermediaries, and that overpayments to these plans divert funds from the traditional program. See medicare-advantage-critical-viewpoint.

Medicare Advantage as beneficial competition - Defenders of Part C argue that private plan competition drives innovation, improves care coordination, and offers beneficiaries additional benefits not available in traditional Medicare. See medicare-advantage-supportive-viewpoint.

Medicare for All - A distinct political and policy position holds that Medicare should be transformed into a universal, single-payer system covering the entire U.S. population, eliminating most private insurance. See medicare-for-all-viewpoint.

Medicare Advantage overpayments - Investigations by the HHS Office of Inspector General, academic researchers, and congressional oversight bodies have documented patterns of diagnosis upcoding and risk-score inflation by Medicare Advantage insurers, allegedly resulting in billions of dollars in excess federal payments. See medicare-advantage-overpayment-controversy.

Drug pricing negotiation - The Inflation Reduction Act of 2022 granted CMS authority to negotiate drug prices directly with pharmaceutical manufacturers, a provision opposed through litigation by several pharmaceutical companies on constitutional and statutory grounds. See medicare-drug-price-negotiation-controversy.

Disproportionate benefit by race and socioeconomic status - Researchers have documented disparities in Medicare utilization, quality of care received, and health outcomes across racial and socioeconomic groups, generating debate over the program's role in either mitigating or reproducing structural inequities. See medicare-health-disparities-controversy.

• medicare-history
• medicare-eligibility-age-debate
• medicare-single-payer-transition-debate
• medicare-means-testing-debate
• medicare-expansion-supportive-viewpoint
• medicare-consensus-administrative-efficiency-consensus
• medicare-consensus-coverage-effects-consensus
• Affordable Care Act
• Social Security
• Medicaid
• us-health-care-system
• medicare-for-all

1. Centers for Medicare & Medicaid Services. “Medicare Program: General Information.” U.S. Department of Health and Human Services. https://www.cms.gov/Medicare/Medicare-General-Information. 2. Boards of Trustees, Federal Hospital Insurance and Federal Supplementary Medical Insurance Trust Funds. 2024 Annual Report of the Boards of Trustees. Washington, D.C.: U.S. Government Publishing Office, 2024. 3. Boccuti, Cristina, and Gretchen Jacobson. “Comparing Medicare Advantage and Traditional Medicare: A Primer.” Kaiser Family Foundation, 2018. 4. Himmelstein, David U., Miraya Jun, Reinhard Busse, Karine Chevreul, Alexander Geissler, Patrick Jeurissen, Sarah Thomson, Marie-Amelie Vinet, and Steffie Woolhandler. “A Comparison of Hospital Administrative Costs in Eight Nations: U.S. Costs Exceed All Others by Far.” Health Affairs 33, no. 9 (2014): 1586-94. 5. Card, David, Carlos Dobkin, and Nicole Maestas. “The Impact of Nearly Universal Insurance Coverage on Health Care Utilization: Evidence from Medicare.” American Economic Review 98, no. 5 (2008): 2242-58. 6. U.S. Department of Health and Human Services, Office of Inspector General. Medicare Advantage: Questionable Use of Health Risk Assessments. OEI-03-17-00471. Washington, D.C.: HHS OIG, 2021. 7. Inflation Reduction Act of 2022, Pub. L. 117-169, 136 Stat. 1818 (2022). 8. Trivedi, Amal N., Alan M. Zaslavsky, Eric C. Schneider, and John Z. Ayanian. “Relationship Between Quality of Care and Racial Disparities in Medicare Health Plans.” JAMA 296, no. 16 (2006): 1998-2004.