Medicare covers people in specific groups, not everyone

Medicare is a federal health insurance program run by the Centers for Medicare & Medicaid Services (CMS). It does not cover the general population. Instead, it covers people who fall into one of four main categories: people 65 and older, people under 65 with certain disabilities, people with end-stage renal disease (ESRD), and people with amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease.

The age threshold of 65 is automatic — you become covered on the first day of the month you turn 65, provided you or your spouse paid Medicare taxes while working. The other three groups must meet specific medical or work-history requirements. This guide explains who falls into each group and what that membership looks like.

Key Takeaways

  • People 65 and older are covered if they or a spouse paid Medicare taxes for at least 10 years of work.
  • People under 65 can be covered if they have been receiving Social Security disability benefits for 24 months, or if they have ESRD or ALS regardless of work history.
  • Medicare has four parts — Part A (hospital), Part B (doctor visits), Part D (prescription drugs), and Part C (an alternative private plan) — and not all are automatic.
  • Enrollment important date exist: missing them can lock you out of coverage or cost you more in premiums, even if you are otherwise covered.
  • Your work history and current income determine whether you pay premiums and how much you pay.

People 65 and older with a work history

The largest group covered by Medicare is people who reach age 65. You are covered automatically if you or your spouse worked and paid Medicare taxes (the 2.9 percent withheld from paychecks) for at least 10 years — 40 quarters of coverage in Social Security terms. You do not have to be retired; you can still be working. You do not have to be a U.S. citizen, but you must be a permanent resident who has lived in the United States for at least five years.

Coverage begins the first day of the month you turn 65. Part A (hospital insurance) is free for most people in this group. Part B (medical insurance for doctor visits and outpatient care) requires a monthly premium, which changes each year. In 2024, the standard Part B premium was $164.90 per month, but higher earners pay more. Part D (prescription drug coverage) is optional and comes from private insurers; you choose a plan or go without.

If you do not sign up for Part B when you first become covered, you will pay a permanent penalty — an extra 10 percent of the standard premium for each year you delayed. The same penalty applies to Part D. The only exception is if you have employer health insurance while you are still working; in that case, you can delay without penalty.

People under 65 receiving disability benefits

People under 65 who receive Social Security Disability Insurance (SSDI) become covered by Medicare after they have been on SSDI for 24 months. The 24-month clock starts from the month you first received a disability payment, not from the month you applied. During those 24 months, you have no Medicare coverage through this route, though you may be covered by Medicaid depending on your state and income.

Once the 24 months are complete, you are covered by the same Medicare parts as someone 65 and older: Part A is free if you have enough work credits, and Part B requires a monthly premium. Your income determines how much you pay for Part B. If your income is below a certain threshold, you pay the standard premium. If it is higher, you pay an income-related surcharge on top of the standard amount.

You stay on Medicare as long as you remain on SSDI, even if you return to work. If your disability benefits end because you have medically improved, your Medicare coverage ends 93 days later. This grace period gives you time to find other coverage.

People with end-stage renal disease or ALS

Two medical conditions grant Medicare coverage regardless of age or work history: end-stage renal disease (ESRD) and amyotrophic lateral sclerosis (ALS). ESRD means your kidneys no longer function and you need dialysis or a transplant to survive. ALS is a progressive neurological disease that affects muscle control.

For ESRD, coverage begins the month you start dialysis or the month after you receive a kidney transplant, whichever comes first. You do not have to wait for a disability information. For ALS, coverage begins the month after you are approved for Social Security disability benefits; you do not have to wait the 24 months that other disability recipients do.

Both groups are covered by Part A and Part B. Part A is free if you have enough work credits; if you do not, you may still be covered but will pay a premium. Part B requires a monthly premium based on your income. These groups can also enroll in Part C (Medicare Advantage) or Part D (prescription drug coverage) through private insurers.

How Medicare parts work and what they cover

Part A covers inpatient hospital stays, skilled nursing facility care after a hospital stay, hospice care, and some home health services. There is no monthly premium if you have 40 work credits. If you do not, you can still buy Part A, but the 2024 premium was $505 per month for people with 30 to 39 work credits, or $1,010 per month for those with fewer than 30 credits. Part A has a deductible: in 2024, you paid $1,632 for each hospital stay.

Part B covers doctor visits, outpatient surgery, diagnostic tests, physical therapy, and durable medical equipment like wheelchairs. The standard 2024 premium was $164.90 per month, but higher earners paid between $247.35 and $560.50 per month depending on their income. Part B also has a deductible ($240 in 2024) and a coinsurance amount (usually 20 percent of the cost after the deductible).

Part D covers prescription drugs through private insurance plans. You choose a plan each year during the enrollment period. Plans vary in which drugs they cover and how much you pay. If you do not enroll in Part D when you first become covered, you pay a permanent penalty if you enroll later — 1 percent of the national average premium for each month you delayed.

Part C, also called Medicare Advantage, is an alternative to Parts A and B. Private insurers offer these plans, which must cover everything Part A and B cover but often include Part D and other benefits like dental or vision. You pay a monthly premium to the private insurer instead of to Medicare. Not all plans are available in all areas.

Work history and premium costs

Your work history determines whether you pay for Part A and how much you pay for Part B. Work credits are earned through payroll taxes. You earn one credit for each $1,730 of wages in 2024 (the amount changes yearly), up to four credits per year. Most people need 40 credits total to may have access to for free Part A; some groups need fewer.

If you do not have enough work credits, you can still be covered by Medicare, but you will pay a premium for Part A. Your spouse's work history can also count: if you are married and your spouse has 40 credits, you may be covered for free Part A even if you do not have 40 credits yourself.

Your income in the current year and the prior year determines your Part B and Part D premiums. The higher your income, the higher your premium. Income thresholds change yearly. If your income drops significantly — because you retire, for example — you can ask Medicare to recalculate your premium based on your current income rather than the prior year's income.

Who is not covered by Medicare

Medicare does not cover people under 65 who do not have a disability, ESRD, or ALS, regardless of income or employment status. It does not cover undocumented immigrants. It does not cover people who have not lived in the United States for the required time (five years for permanent residents, or three of the last five years for some groups).

People in these groups may be covered by Medicaid, the Affordable Care Act marketplace, employer health insurance, or they may be uninsured. Each state runs Medicaid differently, so coverage varies by location. The ACA marketplace offers plans to people under 65 with income between 100 and 400 percent of the federal poverty level, though some people with lower income may may have access to for subsidies.

Enrollment periods and important date

If you become covered by Medicare at 65, you have a seven-month window to enroll in Part B and Part D without penalty. This window is called your Initial Enrollment Period (IEP) and runs three months before the month you turn 65, the month you turn 65, and three months after. If you miss this window and do not have other coverage, you will pay a permanent penalty.

If you become covered through disability or ESRD, you also have an Initial Enrollment Period. For disability, it is the same seven-month window around the month you become covered. For ESRD, it is a different calculation based on when you start dialysis or receive a transplant.

Every year, there is an Annual Enrollment Period (AEP) from October 15 to December 7. During this time, you can change your Part D plan, switch between Original Medicare and Medicare Advantage, or enroll in Part D if you did not before. Missing the AEP means you cannot change plans until the next year, with limited exceptions.

Frequently Asked Questions

Do I have to be a U.S. citizen to get Medicare?

No, but you must be a permanent resident (green card holder) who has lived in the United States for at least five years. Some groups have different residency requirements. Undocumented immigrants are not covered by Medicare.

Can I get Medicare if I never worked?

Not through your own work history. However, if you are married or were married, your spouse's work history may may have access to you for free Part A. If you have ESRD or ALS, you are covered regardless of work history. Otherwise, you would need to look at Medicaid or ACA marketplace coverage.

What happens to my Medicare if I move out of the United States?

You can keep Medicare Part A and Part B if you move abroad, but coverage is limited. Medicare generally does not pay for care outside the U.S., except in rare cases near the border. Part D (prescription drugs) does not work outside the U.S. You should research health insurance in your destination country.

If I am still working at 65, do I have to enroll in Medicare?

You must enroll in Part A, but you can delay Part B if you have employer health insurance through your job. When you stop working or lose that coverage, you have eight months to enroll in Part B without penalty. If you miss that window, you will pay a permanent penalty.

How much does Medicare cost per month?

Part A is free for most people. Part B costs between $164.90 and $560.50 per month in 2024, depending on your income. Part D costs vary by plan, usually between $7 and $100 per month. Part C (Medicare Advantage) costs vary by plan and location. These amounts change yearly.