The Basic Rules for Medicare Coverage

You can get Medicare if you are 65 or older, or if you are under 65 and have received Social Security Disability Insurance (SSDI) for 24 months, or if you have end-stage renal disease or ALS (amyotrophic lateral sclerosis). Most people become covered automatically at 65 if they have already been receiving Social Security benefits — you do not have to do anything. If you have not yet claimed Social Security, you will need to sign up for Medicare separately, even if you do not need the money yet.

Citizenship or legal residency matters. You must be a U.S. citizen or a permanent resident who has lived in the country for at least five consecutive years. If you are not sure whether you meet this requirement, the Social Security Administration (SSA) can tell you during the sign-up process.

The timing of when you sign up affects your costs for the rest of your life. If you wait past the month you turn 65 without a valid reason, you will pay a permanent penalty on your Part B and Part D premiums. That penalty stays with you as long as you have Medicare, so getting the timing right matters.

Key Takeaways

  • You become covered at 65 if you are already receiving Social Security; otherwise you must sign up for Medicare separately even if you delay claiming benefits.
  • If you are under 65, you may still may have access to if you have received SSDI for 24 months, have end-stage renal disease, or have ALS.
  • You must be a U.S. citizen or permanent resident who has lived in the country for at least five consecutive years.
  • Signing up late past your 65th birthday results in permanent premium penalties unless you have employer coverage or another valid reason for the delay.
  • Your initial sign-up window is seven months long, centered on the month you turn 65, and missing it can cost you thousands over time.

What Counts as a Valid Reason to Sign Up Late

The Social Security Administration recognizes certain situations where you can sign up after 65 without paying a penalty. The most common is group health coverage through an employer — if you or your spouse are still working and covered by an employer plan, you can delay Medicare without penalty. You must sign up within eight months of losing that coverage or retiring, whichever comes first.

Other valid reasons include being covered by the Veterans Administration, having coverage through a federal employee health plan, or living outside the United States. If you believe you have a reason that should protect you from the penalty, bring documentation of that coverage when you sign up. The SSA will review it, but the burden is on you to prove the reason was valid.

The Three Paths to Medicare at 65

Most people sign up through the Social Security Administration because it is the simplest route. If you are already receiving Social Security checks, Medicare Part A (hospital coverage) and Part B (doctor visits) start automatically the month you turn 65. You will receive a Medicare card in the mail about three months before your birthday. If you have not yet claimed Social Security, you can still sign up for Medicare alone by calling Social Security at 1-800-772-1213 or visiting your local Social Security office.

You can also sign up online through Medicare.gov, the federal Medicare website. This route works whether or not you have claimed Social Security yet. You will need your Social Security number, proof of citizenship or permanent residency, and information about any current health coverage.

A third option is to visit your local Social Security office in person. Bring your birth certificate, proof of citizenship (passport or naturalization papers), and proof of residency (a recent utility bill or lease). Staff can walk you through the process on the spot, though wait times vary by location.

When to Sign Up: Your Seven-Month Window

Your initial enrollment period runs for seven months: three months before the month you turn 65, the month itself, and three months after. If your birthday is June 15, your window opens March 1 and closes September 30. During this window, you can sign up for Part A and Part B without penalty, regardless of whether you need coverage right away.

If you miss this window and do not have a valid reason (like employer coverage), you enter a different situation. You can still sign up during the general enrollment period, which runs January 1 through March 31 each year. Coverage would not start until July 1 of that year, creating a gap. You would also owe the permanent penalty on Part B premiums — currently 10 percent extra for each full year you were may be able to access but not enrolled, though this amount changes annually.

The penalty for Part D (prescription drug coverage) works the same way. If you go 63 days or more without Part D coverage and do not have other creditable drug coverage, you will pay a permanent penalty when you finally enroll. That penalty is roughly 1 percent of the national average Part D premium for each month you were without coverage.

Special Rules for People Under 65

If you are under 65 and receiving SSDI, you become covered automatically after 24 months of benefits. You do not need to do anything — Medicare Part A and Part B start in the 25th month. You will receive your Medicare card in the mail.

If you have end-stage renal disease (ESRD) or ALS, the rules are different. With ESRD, you can sign up for Medicare as soon as you start dialysis or receive a transplant, even if you are in your 20s or 30s. With ALS, you become covered when ready upon diagnosis — you do not have to wait. Contact Social Security or Medicare to start the process as soon as you receive your diagnosis.

Documents You Will Need

Gather these before you sign up, whether online, by phone, or in person. You will need your Social Security number, birth certificate, and proof of U.S. citizenship or permanent residency. Acceptable citizenship documents include a passport, naturalization certificate, or birth certificate issued by a U.S. state or territory. If you are a permanent resident, bring your green card or I-551 document.

If you are signing up based on disability or ESRD rather than age, you will also need medical documentation. For SSDI, Social Security already has your file, so you may not need to bring anything extra. For ESRD or ALS, bring a letter from your doctor stating the diagnosis and the date it began. If you are signing up based on employer coverage, bring a copy of your health plan documents or a letter from your employer confirming the coverage dates.

What Happens After You Sign Up

Once you sign up, you will receive a Medicare card in the mail within two to four weeks. The card shows your Medicare number and which parts of Medicare you have (Part A, Part B, Part D, or some combination). Keep this card with you — you will need it when you see a doctor or fill a prescription.

Your coverage starts on the first day of the month you turn 65, or the first day of the month after you meet the other requirements (like the 24-month SSDI mark). If you signed up during your initial enrollment period, there is no gap. If you signed up during the general enrollment period, coverage starts July 1 of that year, so you may have months without Medicare coverage.

After you are enrolled, you can make changes during the annual open enrollment period, which runs October 15 through December 7 each year. During this time, you can switch between Original Medicare and Medicare Advantage plans, add or drop Part D coverage, or change which plan you are in. Changes made during open enrollment take effect January 1 of the following year.

Frequently Asked Questions

Do I have to sign up for Medicare at 65 if I am still working?

If you have health coverage through your current employer, you can delay Medicare Part B without penalty. However, you should still sign up for Part A (hospital coverage) at 65, as it is free and has no penalty for late enrollment. Part B is where the penalty applies if you delay without employer coverage.

What if I am not a U.S. citizen but have a green card?

You can get Medicare if you are a permanent resident and have lived in the United States for at least five consecutive years. Bring your green card and proof of your five-year residency (such as tax returns or lease agreements) when you sign up. The five years do not have to be when ready before you turn 65 — they just need to be five years total since you became a permanent resident.

Can I sign up for Medicare online if I have not claimed Social Security yet?

Yes. Visit Medicare.gov and select "Sign Up for Medicare." You will need your Social Security number, birth certificate, proof of citizenship, and proof of residency. The online process takes about 15 minutes. You can also call Social Security at 1-800-772-1213 to sign up by phone.

What is the penalty for signing up late, and does it ever go away?

The Part B penalty is roughly 10 percent of the national average premium for each full year you were may be able to access but not enrolled. The Part D penalty is roughly 1 percent of the national average Part D premium for each month without coverage. These penalties are permanent — they do not decrease or disappear after a certain number of years. They stay with you as long as you have Medicare.

If I am on SSDI and turn 65, do I need to do anything to switch from SSDI to Medicare?

No. You do not switch — you straightforward continue receiving benefits under Medicare instead of SSDI. Your benefits amount stays the same. You will receive a new Medicare card, but your Social Security checks continue without interruption. This transition happens automatically at age 65 or after 24 months of SSDI, whichever comes later.