Who Medicare Covers and How to Know If You're Eligible

Medicare covers people 65 and older, some younger people with disabilities, and people with end-stage renal disease or ALS

Medicare is a federal health insurance program run by the Centers for Medicare & Medicaid Services (CMS). You do not have to be poor or sick to be covered — age is the main threshold. If you are 65 or older and a U.S. citizen or permanent resident, you are covered. If you are younger, you may still be covered if you have been receiving Social Security Disability Insurance (SSDI) for 24 months, have end-stage renal disease (ESRD), or have been diagnosed with amyotrophic lateral sclerosis (ALS).

The program has four parts — Part A (hospital insurance), Part B (medical insurance), Part D (prescription drug coverage), and Part C (Medicare Advantage, an alternative to Parts A and B). Not everyone needs all four, and not all four are mandatory. Understanding which parts explore to you depends on your age, work history, and health status.

Key Takeaways

You become covered at 65 if you are a U.S. citizen or permanent resident, regardless of income or health history.
If you are under 65, you may be covered if you have received SSDI for 24 months, have end-stage renal disease, or have ALS.
Part A (hospital) is usually free if you or your spouse paid Medicare taxes for at least 10 years; Part B (doctor visits) costs a monthly premium.
You must sign up for Part B during your initial enrollment period or face a permanent penalty on your monthly premium.
Part C (Medicare Advantage) and Part D (drug coverage) are optional but have enrollment important date that can affect your costs.

Age 65 and older: automatic coverage and enrollment timing

When you turn 65, you become covered by Medicare if you are a U.S. citizen or have been a permanent resident for at least five years. You do not have to wait for a birthday or a specific date — coverage begins on the first day of the month in which you turn 65. If you are already receiving Social Security benefits, Medicare enrollment happens automatically three months before your 65th birthday. If you are not yet receiving Social Security, you must sign up for Medicare yourself.

Your initial enrollment period runs for seven months: three months before the month you turn 65, the month itself, and three months after. During this window, you can sign up for Part B without a penalty. If you miss this window and do not have other may have access to coverage (such as employer health insurance), you will pay a permanent 10% surcharge on your Part B premium for as long as you have Medicare. This penalty does not go away, so timing matters.

People under 65 with disabilities: the 24-month SSDI rule

If you are under 65 and receiving Social Security Disability Insurance (SSDI), you become covered by Medicare automatically after you have been receiving SSDI for 24 months. The 24 months starts from the date your SSDI benefits began, not from the date you applied. You do not need to do anything — Social Security will enroll you in Parts A and B automatically.

This rule applies whether your disability is physical, mental, or both. Once you reach 65, your Medicare coverage continues under the age-65 rules, and your SSDI status no longer matters for Medicare purposes. If you are unsure whether you have been receiving SSDI for 24 months, you can check your Social Security statement online or call Social Security at 1-800-772-1213.

People with end-stage renal disease or ALS

If you have end-stage renal disease (ESRD) — permanent kidney failure requiring dialysis or a transplant — you become covered by Medicare regardless of age. Coverage typically begins the first month you start dialysis treatment or the month of your kidney transplant. If you receive a pre-emptive transplant (before dialysis), coverage begins the month of the transplant.

If you have been diagnosed with amyotrophic lateral sclerosis (ALS, also called Lou Gehrig's disease), you become covered by Medicare when ready upon diagnosis, regardless of age. You do not have to wait any months or meet any other condition. Social Security will enroll you in Parts A and B automatically once your diagnosis is confirmed.

Part A coverage: who pays and who does not

Part A covers hospital stays, skilled nursing facility care, hospice, and home health services. For most people 65 and older, Part A is free — you pay no monthly premium. This is because you or your spouse paid Medicare taxes (called FICA taxes) while working. You need 40 quarters of Medicare tax payments to may have access to for free Part A, which is roughly 10 years of work.

If you do not have 40 quarters of work history, you can still buy Part A, but you will pay a monthly premium. The amount varies depending on how many quarters you have. If you have 30 to 39 quarters, the premium is lower than if you have fewer than 30. You can check your work history on your Social Security statement at ssa.gov.

Part B coverage: the monthly premium and enrollment important date

Part B covers doctor visits, outpatient care, medical equipment, and preventive services. Unlike Part A, Part B always has a monthly premium. The standard premium in 2024 is $174.70 per month, though it changes each year and may be higher if your income is above a certain threshold. You pay this premium whether you use Medicare or not.

Part B is optional, but signing up during your initial enrollment period (the seven-month window around your 65th birthday) is important. If you delay and do not have other may have access to coverage, you will pay a permanent 10% surcharge for each year you were not enrolled. This penalty stays with you for life. The only exception is if you have employer health insurance through current work — in that case, you can delay Part B without penalty.

Part C and Part D: optional coverage with separate important date

Part C, also called Medicare Advantage, is an alternative way to receive your Part A and Part B benefits. Instead of going to any doctor who accepts Medicare, you choose a plan run by a private insurance company. Part C plans often include prescription drug coverage (Part D) and extra benefits like dental or vision. Part C is optional, and you can choose it or stick with Original Medicare (Parts A and B).

Part D covers prescription drugs. If you choose Original Medicare (not Part C), you must sign up for Part D separately, usually through a standalone plan. If you go without Part D coverage and later sign up, you may pay a permanent surcharge on your premiums. The enrollment important date for Part C and Part D is December 7 each year, and coverage begins January 1. If you miss this important date, you can only sign up during the general enrollment period (January 1 to March 31) or if you have a may have access to life event.

Frequently Asked Questions

What happens if I turn 65 but am still working?

You can delay Part B without penalty if you have health insurance through your current employer. When you stop working, you have eight months to sign up for Part B without a penalty. Tell your employer's benefits office that you are covered by employer insurance so Medicare knows not to charge you a surcharge.

Can I get Medicare if I am not a U.S. citizen?

You can get Medicare at 65 if you are a permanent resident (green card holder) and have lived in the United States for at least five years. If you are not a permanent resident, you are not covered by Medicare, though you may have other options depending on your visa status and state.

Do I have to sign up for all four parts of Medicare?

No. Part A is usually automatic if you are 65 and may be able to access. Part B is optional but has enrollment important date with penalties. Part C and Part D are both optional. However, if you do not sign up for Part D when first may be able to access and later want it, you will pay a surcharge.

What if I was denied SSDI but still have a disability?

If you were denied SSDI, you are not covered by Medicare under the disability rule. You would need to wait until 65 to be covered by Medicare based on age. You may have other health insurance options through your state or the health insurance marketplace.

Does my spouse get Medicare when I do?

No. Your spouse must meet the same rules as you — they must be 65, or under 65 with SSDI for 24 months, ESRD, or ALS. Your work history does not cover them. However, if your spouse has their own work history, they may may have access to for free Part A based on their own earnings.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.