You must enroll in Medicare at 65, but the exact important date depends on your work and insurance history

If you are a U.S. citizen or permanent resident turning 65, you will be automatically enrolled in Medicare Part A (hospital insurance) if you are already receiving Social Security benefits. If you are not yet receiving Social Security, you must take action during your Initial Enrollment Period — the seven-month window that starts three months before the month you turn 65 and ends three months after. Missing this window can cost you permanently higher premiums and gaps in coverage.

Part B (medical insurance) is different. You are not automatically enrolled in Part B, and you must choose whether to take it. If you delay Part B without a valid reason, you will pay a 10 percent penalty on your premium for each year you did not have it — and that penalty is permanent. The same seven-month Initial Enrollment Period applies to Part B.

There is one major exception: if you or your spouse are still working and covered by an employer health plan, you may be able to delay Part B without penalty. This is called creditable coverage, and it requires that your employer plan covers at least 20 employees. You will need to document this coverage when you do enroll.

Key Takeaways

  • You must enroll in Medicare during your Initial Enrollment Period — the seven months surrounding your 65th birthday — or face permanent premium penalties.
  • Part A (hospital insurance) is usually automatic if you receive Social Security, but you must enroll yourself if you do not yet claim benefits.
  • Part B (medical insurance) requires a separate choice; you are not automatically enrolled, and delaying it without employer coverage costs you 10 percent more per year permanently.
  • If you are still working and covered by an employer plan with at least 20 employees, you may delay Part B without penalty, but you must prove this coverage when you enroll later.
  • Missing your Initial Enrollment Period does not prevent you from enrolling later, but you will pay higher premiums unless you have a valid reason for the delay.

When you can delay enrollment without a penalty

The main reason to delay Part B without penalty is group health plan coverage through your own job or your spouse's job. The plan must be from an employer with at least 20 employees. If this applies to you, you can continue your employer coverage past 65 and enroll in Part B later without the 10 percent penalty.

When you do leave that job or lose the coverage, you have eight months to enroll in Part B without penalty. This is called your Special Enrollment Period. You will need to show proof that you had employer coverage — usually a letter from your employer's benefits department stating the plan name, dates of coverage, and the number of employees.

If you are not yet receiving Social Security at 65, you must still enroll in Part A during your Initial Enrollment Period, even if you have employer coverage. Part A has no premium for most people, so there is no penalty for delaying it, but enrolling on time keeps your record clean.

What happens if you miss your enrollment important date

If you do not enroll in Part B during your Initial Enrollment Period and you do not have a valid reason (such as employer coverage), you will pay a permanent 10 percent increase on your Part B premium for each full year you delayed. This penalty stays with you for life, even after you finally enroll.

You can still enroll in Part B during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. However, the penalty applies unless you can show you had creditable coverage or another may have access to reason for the delay.

The same permanent penalty applies to Part D (prescription drug coverage). If you go 63 or more days without creditable drug coverage after your Initial Enrollment Period ends, you will pay a penalty when you enroll. The amount varies by year and region.

How to know if you are automatically enrolled

If you are receiving Social Security benefits before you turn 65, Social Security will automatically enroll you in Part A and Part B about three months before your 65th birthday. You will receive a Medicare card in the mail. You do not need to do anything unless you want to decline Part B, which you can do by returning a form that comes with your card.

If you are not yet receiving Social Security at 65, you are not automatically enrolled in anything. You must contact Social Security or Medicare to enroll in Part A. You can do this online at ssa.gov, by phone at 1-800-772-1213, or in person at your local Social Security office.

If you are still working and covered by an employer plan, tell Medicare about it when you enroll. You will need the name of your employer, the plan name, and the number of employees. This documentation protects you from penalties if you delay Part B.

Special situations where enrollment rules differ

If you are a federal employee, railroad retiree, or covered under TRICARE (military health coverage), your enrollment rules may differ. Federal employees and railroad retirees have their own health plans and may have different important date. TRICARE beneficiaries must enroll in Part A and Part B at 65 or lose TRICARE coverage for life.

If you are not a U.S. citizen but are a permanent resident (green card holder), you can enroll in Medicare at 65 the same way as a citizen. If you are in the U.S. on a visa or temporary status, you cannot enroll in Medicare.

If you are receiving disability benefits from Social Security before 65, you are already enrolled in Medicare Part A and Part B automatically. You do not need to take any action at 65 — your coverage straightforward continues.

How to enroll if you have not been automatically enrolled

Contact Social Security to enroll in Part A. You can explore online at ssa.gov, call 1-800-772-1213, or visit a local Social Security office. You will need your birth certificate, proof of citizenship or permanent residency, and your Social Security number. Enrollment usually takes about two weeks.

To enroll in Part B, you can use the same Social Security channels, or you can contact Medicare directly at 1-800-MEDICARE (1-800-633-4227). If you are enrolling late and believe you have a valid reason for the delay, tell them at this time — you may be able to avoid the penalty if you can document your reason.

If you are declining Part B because you have employer coverage, you must submit a form stating this. Social Security or Medicare will give you the form, or you can find it at cms.gov. Keep a copy for your records.

Understanding Part D enrollment and penalties

Part D (prescription drug coverage) has its own enrollment rules and penalties. You must enroll in Part D during your Initial Enrollment Period or during the annual enrollment period (October 15 through December 7 each year). If you delay without creditable drug coverage, you will pay a penalty when you enroll.

Creditable drug coverage means your current insurance (such as an employer plan or retiree plan) covers prescription drugs at least as well as Medicare Part D. If you have this coverage, you can delay Part D without penalty. You will need proof from your plan that it is creditable — usually a letter or notice sent to you each year.

The Part D penalty is calculated based on the national average premium at the time you enroll, multiplied by the number of months you were without coverage. Like the Part B penalty, it is permanent.

Frequently Asked Questions

What if I turn 65 but am not ready to retire?

You still must enroll in Medicare during your Initial Enrollment Period. If you have employer coverage through your job, you can delay Part B without penalty, but you must enroll in Part A. Continuing to work does not change your Medicare enrollment important date.

Can I decline Medicare entirely and keep only my employer plan?

You cannot decline Part A if you are receiving Social Security benefits — it is automatic. You can decline Part B if you have employer coverage, but you must do so in writing during your Initial Enrollment Period. Once you lose the employer coverage, you will need to enroll in Part B, and any delay will result in a penalty unless you act within eight months.

Do I have to enroll in all four parts of Medicare?

No. Part A is usually automatic. Part B is optional but recommended; delaying it without employer coverage costs you permanently. Part D (drug coverage) is optional, but delaying it without creditable drug coverage also costs you a permanent penalty. Part C (Medicare Advantage) is an alternative to Parts A and B, not an addition.

What if I miss the important date but have a good reason?

Social Security and Medicare recognize certain reasons for late enrollment, such as employer coverage, military service, or living outside the U.S. If you have one of these reasons, you may avoid the penalty. Contact Social Security or Medicare and explain your situation — have documentation ready, such as a letter from your employer or proof of where you were living.

Can I change my mind after I enroll?

Yes, during the annual enrollment period (October 15 through December 7), you can change your coverage. You can switch between Original Medicare and Medicare Advantage, add or drop Part D, or make other changes. Changes take effect January 1 of the following year.