You enroll in Medicare Part A and Part B during specific windows, and the timing depends on whether you're turning 65 or leaving employer coverage

Most people become may be able to access for Medicare at 65. If you're already receiving Social Security, Medicare will enroll you automatically in Part A (hospital insurance) and Part B (medical insurance) three months before your 65th birthday. You'll receive your Medicare card in the mail. If you're not yet taking Social Security, you must contact Social Security or Medicare yourself to enroll — nothing happens automatically.

The enrollment window that matters most is your Initial Enrollment Period, which runs for seven months: three months before the month you turn 65, the month itself, and three months after. If you miss this window and don't have may have access to coverage (like an active employer plan), you'll face a permanent penalty on your Part B premium for as long as you have Medicare.

If you're still working and covered by your employer's health plan, you can delay Part B without penalty, but you must enroll in Part A. Part A has no premium for most people, and enrolling protects you if you need hospital care before you retire.

Key Takeaways

  • If you receive Social Security, Medicare enrolls you automatically three months before you turn 65 — you do not need to do anything.
  • If you do not receive Social Security, you must contact Social Security or Medicare to enroll during your Initial Enrollment Period (seven months centered on your 65th birthday).
  • Missing your enrollment window triggers a permanent penalty on Part B premiums unless you had employer coverage that qualifies as creditable coverage.
  • Part A (hospital insurance) has no premium for most people and should be enrolled even if you delay Part B because you're still working.
  • You can enroll online at Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

Automatic enrollment through Social Security

If you're receiving Social Security benefits when you turn 65, Social Security and Medicare coordinate automatically. Three months before your birthday, Social Security will send you a notice telling you that you've been enrolled in Part A and Part B. Your Medicare card will arrive in the mail about two weeks before your 65th birthday.

You don't need to do anything. The enrollment is complete. Your Part A coverage and Part B coverage both start on the first day of the month you turn 65. Part A has no premium for most people. Part B has a monthly premium that will be deducted from your Social Security check.

Check the notice carefully. If it says you've been enrolled in Part B but you're still working and covered by your employer's plan, you have a short window to decline Part B without penalty. You must contact Social Security or Medicare within the timeframe shown in the notice to opt out of Part B only — you cannot decline Part A.

Manual enrollment if you don't receive Social Security

If you're not receiving Social Security at 65, you must enroll in Medicare yourself. Social Security will not do it for you. Contact Social Security or Medicare during your Initial Enrollment Period — the seven-month window centered on your 65th birthday.

You can enroll online at Medicare.gov, by calling 1-800-MEDICARE (1-800-633-4227), or by visiting your local Social Security office in person. Online enrollment is the fastest route and you can complete it in one sitting. By phone, expect to wait 15 to 30 minutes during business hours, and the representative will walk you through the form. In person, bring your Social Security number, proof of citizenship or legal residency, and proof of age (birth certificate or passport).

When you enroll, you'll be asked whether you want Part A, Part B, or both. If you're still working and have employer coverage, you can enroll in Part A only and delay Part B. If you're retired or not covered by an employer plan, enroll in both.

Delaying Part B if you have employer coverage

If you're still working at 65 and your employer offers health insurance, you can delay Part B without penalty — but only if your employer plan is considered creditable coverage. Creditable coverage means the plan covers at least as much as Medicare Part B does. Most employer plans meet this standard.

To delay Part B safely, you must have written proof that your employer plan is creditable. Ask your employer's benefits department for a creditable coverage letter. Keep this letter. When you eventually leave your job and want to enroll in Part B, you'll show this letter to prove you had may have access to coverage and avoid the late-enrollment penalty.

You still must enroll in Part A at 65, even if you delay Part B. Part A covers hospital stays, and you want that protection in place. Enroll in Part A during your Initial Enrollment Period through Social Security or Medicare.

What documents you need to enroll

Enrollment itself requires minimal paperwork. You'll need your Social Security number and proof of age. If you're enrolling online or by phone, you don't need to submit documents upfront — you just provide the information verbally or type it in. If you're enrolling in person at a Social Security office, bring your birth certificate, passport, or state ID.

If you're delaying Part B because of employer coverage, gather your creditable coverage letter from your employer's benefits department before you enroll. You don't submit it during enrollment, but you'll need it later when you do enroll in Part B, so keep it in a safe place.

If you're enrolling after your Initial Enrollment Period has ended (because you missed it or because you're newly may be able to access due to a life event), you may need to provide additional proof — such as documentation that you had employer coverage or that you experienced a may have access to event like loss of coverage. Medicare will tell you what's needed when you contact them.

What happens after you enroll

Once you enroll, your Part A and Part B coverage begins on the first day of the month you turn 65 (or the first day of the month after you enroll, if you enroll after your birthday). You'll receive your Medicare card in the mail within two weeks. The card shows your Medicare number, which you'll use to identify yourself to doctors and hospitals.

Part A has no premium for most people. Part B has a monthly premium that varies by income. If you enrolled through Social Security, the premium is deducted automatically from your Social Security check. If you enrolled through Medicare directly, you'll receive a bill for Part B premiums, usually monthly.

You're now covered for Part A services (hospital stays, skilled nursing, hospice, home health) and Part B services (doctor visits, outpatient care, preventive services). You'll have a deductible and coinsurance for both parts. Review your coverage details in the welcome packet that comes with your card, or log into your Medicare account at Medicare.gov to see what's covered.

Frequently Asked Questions

What if I turn 65 while still working?

You can delay Part B if your employer offers health insurance, but you must enroll in Part A. Contact Social Security or Medicare during your Initial Enrollment Period to enroll in Part A only. Get a creditable coverage letter from your employer so you can prove later that you had may have access to coverage when you do enroll in Part B.

Can I enroll after my Initial Enrollment Period ends?

Yes, but you may face a permanent penalty on your Part B premium unless you had creditable coverage (like an employer plan) during the time you were uninsured. Contact Medicare to discuss your situation and enroll as soon as possible. The longer you wait, the higher your penalty will be.

Do I have to take Part B if I'm automatically enrolled?

If Social Security enrolls you automatically and you're still working with employer coverage, you can decline Part B within the timeframe shown in your enrollment notice. You cannot decline Part A. Contact Social Security or Medicare right away if you want to opt out of Part B.

What's the difference between Part A and Part B?

Part A covers hospital stays, skilled nursing care, hospice, and home health services. Part B covers doctor visits, outpatient procedures, preventive care, and medical equipment. Most people need both, but if you're still working and covered by an employer plan, you can delay Part B.

How do I know if my employer plan is creditable coverage?

Ask your employer's benefits or HR department directly. They should provide a written creditable coverage letter that states your plan meets Medicare's standards. Keep this letter — you'll need it if you enroll in Part B later and want to avoid a late-enrollment penalty.