You can enroll in Medicare Part A and Part B during specific windows, and the timing affects whether you pay a penalty

Medicare Part A (hospital insurance) and Part B (medical insurance) have open enrollment periods set by Social Security and Medicare. Most people become may be able to access at 65, but you can start the process a few months before that date. The key is knowing which enrollment window applies to you — missing it can mean paying higher premiums for as long as you have Medicare.

You do not have to enroll in both parts at the same time, though most people do. Part A is usually free if you or your spouse paid Medicare taxes while working. Part B requires a monthly premium, which varies by income and changes each year.

Key Takeaways

  • You can enroll starting three months before the month you turn 65, during the month you turn 65, and for three months after — this is your Initial Enrollment Period.
  • If you delay Part B past your Initial Enrollment Period and do not have other may have access to coverage, you will pay a permanent 10% increase to your Part B premium for each year you waited.
  • You enroll through Social Security (in person, by phone, or online at ssa.gov), Medicare.gov, or by calling 1-800-MEDICARE.
  • If you are still working and have health insurance through your employer, you may be able to delay Part B without penalty — ask your employer's benefits office about creditable coverage.
  • Part A enrollment is automatic if you are already receiving Social Security benefits; you only need to act if you want to delay or if you have never worked in the U.S. system.

Your Initial Enrollment Period: The three-month window before and after 65

Your Initial Enrollment Period runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after. For example, if you turn 65 in June, your window opens in March and closes in September.

During this window, you can enroll in Part A, Part B, or both without waiting and without penalty. This is the easiest time to sign up. If you miss this window, you may face a permanent premium penalty on Part B — and you may have to wait until the next General Enrollment Period (January 1 to March 31 each year) to enroll.

You do not have to wait until the month you turn 65. Many people enroll two or three months early so coverage starts on the first day of the month they turn 65. Medicare coverage typically begins on the first day of the month in which you turn 65, or the first day of the month after you enroll, whichever is later.

Where to enroll: Social Security, Medicare.gov, or by phone

You have three main routes to enroll. Social Security handles Part A and Part B enrollment and can be reached online at ssa.gov, by phone at 1-800-772-1213 (TTY 1-800-325-0778), or in person at your local Social Security office. You can also call Medicare directly at 1-800-MEDICARE (1-800-633-4227) to enroll in both parts.

If you enroll online through ssa.gov, you will need a Social Security account. The process takes about 10 minutes and you can complete it from home. If you call, a representative will walk you through the questions and confirm your enrollment over the phone. If you go in person to a Social Security office, bring your birth certificate, proof of citizenship or legal residency, and your Social Security card.

Whichever method you choose, have ready: your date of birth, your Social Security number, information about any current health coverage (employer insurance, COBRA, or other plans), and your bank account details if you want your Part B premium deducted automatically.

Part A enrollment: Usually automatic if you get Social Security

If you are already receiving Social Security retirement, survivor, or disability benefits, Medicare Part A enrollment happens automatically three months before you turn 65. You do not need to do anything. You will receive a Medicare card in the mail about two weeks before your coverage starts.

If you are not yet receiving Social Security benefits, you will need to enroll in Part A when you enroll in Part B. You can do this through Social Security or Medicare using the same contact methods listed above.

Part A is premium-free for most people — you paid for it through payroll taxes (Medicare tax) while you worked. If you did not pay Medicare taxes for at least 40 quarters (10 years), you may have to pay a monthly premium for Part A. Social Security or Medicare will tell you the amount when you enroll.

Part B enrollment: Premium, timing, and the penalty for delay

Part B requires a monthly premium. The standard premium for 2024 is $164.90 per month, but the amount changes each year and is higher if your income is above a certain threshold. You pay the premium whether you use Medicare or not.

If you enroll in Part B during your Initial Enrollment Period, your coverage starts on the first day of the month you turn 65 (or the first day of the month after you enroll, if that is later). If you enroll after your Initial Enrollment Period ends and you do not have other may have access to coverage, your coverage will not start until the following January 1, and you will owe a permanent 10% increase to your Part B premium for each full year you delayed.

For example, if you turn 65 in June 2024 but do not enroll in Part B until March 2025 (nine months late), you will pay an extra 10% on your Part B premium for life. If you delay two years, the penalty is 20%. This penalty does not go away.

Delaying Part B without penalty: Employer coverage and creditable coverage

You can delay Part B past your Initial Enrollment Period without penalty if you or your spouse are still working and have creditable coverage through an employer health plan. Creditable coverage means the plan is at least as good as Medicare Part B.

If this applies to you, ask your employer's benefits or human resources office whether your plan is creditable. Get this in writing. When you leave the job or lose the coverage, you will have eight months to enroll in Part B without penalty — this is called your Special Enrollment Period.

If you have COBRA, retiree health coverage, or coverage through a spouse's employer, check with that plan's administrator to confirm it counts as creditable coverage. Not all plans do.

What happens after you enroll

After you enroll, Medicare will mail you a red, white, and blue Medicare card. This usually arrives within two weeks, though it can take up to four weeks. Your coverage begins on the date Medicare confirms — usually the first of the month you turn 65, or the first of the month after you enroll.

If you enrolled in Part B, your premium will be deducted from your Social Security check each month (if you receive benefits) or you will receive a bill. You can change how you pay by contacting Medicare.

Keep your Medicare card with you and show it to doctors, hospitals, and pharmacies. If you need to make changes to your coverage later — such as adding prescription drug coverage (Part D) or switching to a Medicare Advantage plan — you can do that during the Annual Enrollment Period (October 15 to December 7 each year).

Frequently Asked Questions

What if I miss my Initial Enrollment Period?

You can still enroll during the General Enrollment Period (January 1 to March 31 each year), but your coverage will not start until July 1 of that year, and you will owe a permanent 10% penalty on your Part B premium for each year you delayed — unless you have creditable coverage through an employer. Contact Medicare or Social Security right away to understand your options.

Do I have to enroll in Part B if I have employer coverage?

No. If you or your spouse are still working and have creditable coverage through an employer plan, you can delay Part B. When you leave the job or lose coverage, you will have eight months to enroll without penalty. Tell Medicare or Social Security about your employer coverage when you enroll in Part A.

Can I enroll in Part A without Part B?

Yes. You can enroll in Part A alone and delay Part B if you have other coverage or do not need it yet. However, if you delay Part B past your Initial Enrollment Period without creditable coverage, you will pay a penalty. It is usually better to enroll in both during your Initial Enrollment Period to avoid the penalty.

What if I am not a U.S. citizen?

You can enroll in Medicare if you are a permanent resident (green card holder) and have lived in the U.S. for at least five years, or if you are a citizen. Bring proof of legal residency and your Social Security number when you enroll. Contact Social Security or Medicare if you have questions about your status.

Can I change my mind after I enroll?

Yes, but only during certain windows. You can change your coverage during the Annual Enrollment Period (October 15 to December 7) or if you have a may have access to life event, such as losing employer coverage. Contact Medicare to discuss your options.