Personal Finance & Estate › IRS, SSA, CMS & other agencies
Centers for Medicare & Medicaid Services (CMS)
Since 1977 (as HCFA)· Agency
Law or rule (2026)Set by statute, regulation or the agency; numbers change yearly.
The federal agency that runs Medicare, oversees Medicaid with the states, and operates the federal ACA marketplace.
See it on the Personal Finance & Estate map →How it works
CMS, part of the U.S. Department of Health and Human Services, runs Medicare, oversees Medicaid and CHIP with the states, and operates the federal ACA marketplace, together covering about 150 million people. It sets Part B premiums and IRMAA tiers, approves Medicare Advantage and Part D plans, and pays hospitals and doctors. Created in 1977 as the Health Care Financing Administration, it was renamed in 2001. Medicare.gov's Plan Finder and Care Compare tools rate plans, nursing homes and home-health agencies.
Why it matters for you
Its rules decide what Medicare covers, what retirees pay and which nursing homes pass inspection; Care Compare star ratings are a practical first check when choosing care for a parent.
Rules, limits and sources (2026)
CMS publishes enrollment, spending and inspection data; national health expenditure accounts show Medicare and Medicaid spent about $1.9 trillion combined in 2023.
Watch out for
How the 2025 law's Medicaid cuts, which the Congressional Budget Office projects at nearly $1 trillion over ten years, will play out across states is uncertain.
Inside this (1)
Connections (2)
▸California Dept. of Health Care Services (DHCS) runs Medi-Cal with funding via Centers for Medicare & Medicaid Services (CMS)Law or rule (2026)
How they connect
Medicaid is a federal-state partnership: CMS sets minimum rules, approves California's state plan and waivers, and pays a share of costs, about half for most enrollees and 90% for adults added by the ACA expansion. DHCS designs the details, contracts with managed-care plans and counties, and answers to CMS audits.
When it applies
Medi-Cal began in 1966 under the 1965 Medicaid law; DHCS took over in 2007, and CMS approved the CalAIM waivers reshaping Medi-Cal in 2021.
The rule
California's Medicaid state plan, Section 1115 waivers and federal matching rates are public on CMS and DHCS websites.
Watch out for
How the 2025 federal law's work requirements, due to start by 2027, and tighter limits on provider taxes will shift costs onto California is still being estimated.
▸Medicare (federal health insurance at 65+) is run by Centers for Medicare & Medicaid Services (CMS)Law or rule (2026)
How they connect
CMS runs Medicare: it sets premiums and coverage rules, contracts with private firms that process claims, approves Medicare Advantage and Part D plans, and pays providers. SSA handles enrollment and premium deductions, while CMS answers benefit questions through 1-800-MEDICARE and Medicare.gov.
When it applies
Medicare began in 1966 under the Social Security Administration; the Health Care Financing Administration took it over in 1977 and was renamed CMS in 2001.
The rule
Title XVIII of the Social Security Act sets Medicare's rules; the Medicare Trustees Report and CMS data show enrollment, spending and plan payments.
Watch out for
Medicare Advantage now enrolls over half of beneficiaries; whether CMS overpays these private plans, as Congress's advisory commission MedPAC estimates, is hotly debated.