Federal law makes four groups eligible for Medicare: people 65 and older, people under 65 who have received Social Security Disability Insurance (SSDI) for 24 months, people of any age with End-Stage Renal Disease (ESRD), and people diagnosed with Amyotrophic Lateral Sclerosis (ALS).
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Turning 65
You are eligible on the first day of the month you turn 65 (or the prior month if your birthday is on the first). U.S. citizens and lawful permanent residents who have lived in the country for at least 5 continuous years qualify.
Premium-free Part A
You get Part A at no premium if you (or a spouse) have at least 40 quarters of Medicare-covered employment — roughly 10 years of paying Medicare payroll taxes. Fewer than 40 quarters means you can still buy Part A: $285/month with 30–39 quarters, $518/month with fewer, in 2025.
Disability (SSDI)
People under 65 receiving SSDI qualify for Medicare after 24 months of benefits (the "24-month rule"), effective the 25th month. There is no waiting period for people with ALS: Medicare begins the month SSDI payments begin.
End-Stage Renal Disease
People of any age with permanent kidney failure requiring dialysis or transplant qualify for Medicare. Coverage generally begins the fourth month of dialysis (sooner in specific circumstances) and continues 36 months after a successful transplant.
Automatic vs. self-enrollment
- Already receiving Social Security retirement benefits at 65: automatic enrollment in Part A and Part B.
- Already receiving SSDI for 24 months: automatic enrollment.
- Everyone else — including anyone deferring Social Security past 65 — must actively enroll through the Social Security Administration.
Medicare and Medicaid together (dual eligible)
Roughly 12 million Americans qualify for both Medicare and Medicaid. Medicaid income and asset thresholds vary by state and program tier (QMB, SLMB, QI). Dual-eligible beneficiaries pay little to no Medicare cost-sharing and typically qualify for the Extra Help subsidy on Part D. State Health Insurance Assistance Programs (SHIPs) can walk you through eligibility for free.
Non-citizen and residency rules
Non-citizens legally residing in the U.S. must be lawfully present for 5 continuous years and be 65 or older to buy premium Part A and Part B. There is no free Part A for those who have not accrued the required work quarters through their own or a spouse's employment.