Medicare is designed to help three main groups: Americans 65 and older, younger people with certain disabilities, and people with specific serious medical conditions. About 69.7 million people are currently enrolled, with roughly 90% qualifying through age and the remaining 10% through disability or medical diagnosis.
Adults 65 and Older
The largest group Medicare serves is Americans who have reached age 65. If you’ve worked and paid payroll taxes for enough years to qualify for Social Security benefits, you’re entitled to premium-free hospital coverage (Part A) once you turn 65. If you’re already receiving Social Security checks at least four months before your 65th birthday, enrollment is automatic. Your Medicare card arrives in the mail without any action on your part.
People who haven’t accumulated enough work history can still enroll in Medicare at 65, but they’ll pay a monthly premium for Part A and must actively sign up through the Social Security Administration. To qualify this way, you need to be a U.S. citizen or a lawful permanent resident who has lived in the country for at least five continuous years.
People Under 65 With Disabilities
If you’re younger than 65 and receiving Social Security Disability Insurance (SSDI), Medicare kicks in after you’ve collected disability benefits for 24 months. That waiting period is a full two years from the time your disability payments begin, not from the date you first applied or became unable to work. Three months before your coverage starts, you’ll receive a welcome package with your Medicare card.
This pathway covers a wide range of conditions. Any disability severe enough to qualify for SSDI also qualifies for Medicare after the 24-month mark. About 10% of all Medicare beneficiaries are under 65 and enrolled through this route.
People With ALS or Kidney Failure
Two diagnoses bypass the normal waiting periods entirely. People with ALS (Lou Gehrig’s disease) qualify for Medicare as soon as their SSDI benefits begin, with no 24-month wait.
People with end-stage renal disease (permanent kidney failure requiring dialysis or a transplant) can get Medicare at any age, regardless of whether they’re 65 or disabled. You qualify if you, your spouse, or a parent you depend on has enough work history under Social Security. For dialysis patients, coverage typically starts on the first day of the fourth month of treatments. That timeline can move up to the first month if you’re training for home dialysis at a certified facility. For transplant patients, coverage can begin the month you’re admitted to the hospital for the procedure.
One important distinction: if you have Medicare solely because of kidney failure, your coverage has an end date. It stops 12 months after you discontinue dialysis or 36 months after a successful kidney transplant.
What Medicare Actually Covers
Medicare has four parts, each addressing a different category of health care costs. Part A covers hospital stays. Part B covers doctor visits, lab work, outpatient services, and medical equipment. Part C (commonly called Medicare Advantage) bundles Parts A and B into a private insurance plan, often with added perks. Part D helps pay for prescription drugs.
A major change took effect in 2025: prescription drug costs under Part D are now capped at $2,000 per year in out-of-pocket spending. Before this cap, people taking expensive medications for conditions like cancer or rheumatoid arthritis could face thousands more in annual drug costs. The cap applies regardless of how many prescriptions you fill or how costly they are.
More than half of all Medicare beneficiaries, 54%, now use Medicare Advantage rather than original Medicare. That share has grown dramatically, from 8 million people in 2007 to 33 million in 2024. Many enrollees choose these plans for lower premiums, reduced copays, and extra benefits like dental or vision coverage. Some don’t get to choose: a growing number of employers, including state government agencies, have structured their retiree health benefits so they only count toward Medicare Advantage plans.
Low-Income Beneficiaries
Medicare wasn’t designed as a free program. Most enrollees pay premiums, deductibles, and copays that can add up quickly. For people with limited income, several assistance programs fill the gaps.
About 12 million Americans are “dually eligible,” meaning they qualify for both Medicare and Medicaid. This group includes 7.2 million low-income seniors and 4.8 million people with disabilities. When someone has both programs, Medicare pays first for covered services, and Medicaid picks up remaining costs up to the state’s payment limit. Medicaid also covers services Medicare doesn’t, including long-term nursing facility care, eyeglasses, and hearing aids.
Even if you don’t qualify for full Medicaid, Medicare Savings Programs can help pay your premiums and out-of-pocket costs. The thresholds vary by program. The broadest option, the Qualifying Individual program, covers your Part B premium if your monthly income is below $1,816 as an individual or $2,455 as a married couple, with resources under $9,950 (individual) or $14,910 (couple). The Qualified Medicare Beneficiary program, which covers the most costs, has a lower income cutoff of $1,350 per month for individuals.
For prescription drugs specifically, the Extra Help program reduces or eliminates Part D deductibles and copays for people with limited income and resources. Eligibility is determined through the Social Security Administration based on your financial situation.
Who Medicare Doesn’t Cover
Medicare is not universal health insurance. Adults under 65 who are healthy but uninsured don’t qualify. Neither do recent immigrants who haven’t met the five-year residency requirement. People who haven’t worked enough to earn Social Security credits and can’t pay the Part A premium are also left out, though their spouses’ work history can sometimes fill the gap. Children and younger adults without qualifying disabilities generally rely on employer insurance, marketplace plans, Medicaid, or the Children’s Health Insurance Program instead.