Overview: Medicare is the federal health insurance program for seniors and certain individuals with disabilities. Before diving into what it covers, you need to understand who qualifies — and on what terms.

Who Qualifies for Medicare

The standard eligibility rule is straightforward: any U.S. citizen or lawful permanent resident who has lived continuously in the United States for at least five years and is age 65 or older may enroll in Medicare. That said, the financial terms of Part A depend on work history.

To receive premium-free Part A (hospital insurance), you or your spouse must have worked and paid Medicare payroll taxes for at least 40 quarters — the equivalent of ten years of covered employment. Nearly 99% of beneficiaries meet this threshold, so they pay nothing for Part A. Those with 30 to 39 quarters of covered employment may purchase Part A for a reduced premium (around $311/month in 2026), and those with fewer than 30 quarters pay the full premium (around $565/month in 2026). Everyone enrolling in Part B (medical insurance) pays a monthly premium, regardless of work history. The standard 2026 Part B premium is $202.90 per month, though higher-income beneficiaries pay a surcharge called the Income-Related Monthly Adjustment Amount (IRMAA).

Qualifying Before Age 65

Individuals under 65 can qualify for Medicare through three specific pathways:

1. Long-term disability (SSDI or RRB). A person who has been receiving Social Security Disability Insurance (SSDI) or Railroad Retirement Board (RRB) disability benefits is automatically enrolled in Medicare Parts A and B after a mandatory 24-month waiting period. Coverage begins on the 25th month of disability benefits. The waiting period exists because Medicare is intended for long-term, not short-term, disability.

2. Amyotrophic Lateral Sclerosis (ALS / Lou Gehrig's Disease). Because ALS progresses so rapidly, Congress waived the waiting period entirely. A person approved for SSDI due to ALS is enrolled in Medicare the first month disability benefits begin — no 24-month delay.

3. End-Stage Renal Disease (ESRD). Permanent kidney failure requiring dialysis or a kidney transplant triggers Medicare eligibility at any age, provided the individual (or their spouse or parent) has a qualifying work history. Coverage timing varies: for in-center dialysis, Medicare begins in the fourth month of regular dialysis; for home dialysis begun through a training program at a Medicare-approved facility, coverage can start in the first month; for a transplant, coverage begins the month of hospital admission for the transplant.

One important note for the exam: SSI (Supplemental Security Income) alone does not qualify someone for Medicare. SSI is a needs-based income program; Medicare eligibility requires either age 65+ or one of the specific medical conditions above.