You must enroll in Medicare Part B during specific windows, or you may pay a penalty for as long as you have Medicare

Medicare Part B covers doctor visits, outpatient care, and medical equipment. Unlike Part A (hospital insurance), which most people get automatically at 65, you must actively enroll in Part B. The enrollment window that matters most is your Initial Enrollment Period — a seven-month span centered on your 65th birthday. If you miss it and do not have other coverage, you will pay a permanent surcharge on your Part B premium.

The exact timing depends on when you were born and whether you are already receiving Social Security. If you wait past your window without a valid reason, Medicare will add 10 percent to your Part B premium for each full 12 months you were may be able to access but not enrolled. That penalty stays with you for life.

Key Takeaways

  • Your Initial Enrollment Period runs for seven months: three months before your 65th birthday, the month you turn 65, and three months after.
  • If you are already getting Social Security, Medicare will enroll you in Part B automatically unless you actively decline it.
  • If you delay Part B because you have employer coverage, you can enroll without penalty during an eight-month window after that coverage ends.
  • Missing your enrollment window without creditable coverage triggers a permanent 10 percent annual surcharge on your Part B premium.
  • You can enroll online through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

Your Initial Enrollment Period: The seven-month window around your 65th birthday

Your Initial Enrollment Period starts three months before the month you turn 65 and ends three months after. For example, if you turn 65 in June, your window opens in March and closes in September. During this time, you can enroll in Part B without waiting and without penalty, even if you do not yet need it.

The month you enroll matters. If you sign up in the month you turn 65 or earlier, your coverage starts the first day of the month you turn 65. If you enroll in the first month after your birthday, coverage starts the first day of the following month. If you enroll in the second or third month after your birthday, there is a one-month delay — your coverage will not start until two months after you enroll.

This timing can affect your out-of-pocket costs. If you have a doctor's appointment scheduled for the month after your birthday, enrolling before your birthday ensures you have coverage for that visit.

Automatic enrollment if you are already receiving Social Security

If you are already collecting Social Security benefits when you turn 65, Medicare will enroll you in both Part A and Part B automatically. You do not have to do anything. Your Part B coverage will start on the first day of the month you turn 65.

You can decline this automatic enrollment if you have other health coverage through an employer or union. To decline, contact Social Security before your 65th birthday or within three months after. You will receive a notice in the mail explaining your options — read it carefully, because declining Part B means you must have creditable coverage (coverage at least as good as Medicare) to avoid the penalty later.

Delaying Part B if you have employer or union coverage

If you are still working at 65 and have health insurance through your employer or union, you can delay Part B without penalty. This is called having creditable coverage. You do not need to enroll in Part B while you are covered by that plan, even if you are already on Medicare Part A.

When your employer coverage ends — whether because you retire, leave the job, or the plan closes — you have eight months to enroll in Part B without penalty. This is your Special Enrollment Period. The eight months start the month after your coverage ends. If your employer coverage ends in March, your eight-month window runs from April through November.

You must enroll during this eight-month window. If you wait until after it closes, you will owe the permanent surcharge. Bring documentation of your employer coverage — your insurance card, a letter from your employer's benefits office, or your final benefits statement — when you enroll, to show Medicare you had creditable coverage.

How to enroll in Part B

You have three main ways to enroll. The fastest is online at Medicare.gov. Go to the "Sign Up for Medicare" section, create a Medicare.gov account if you do not have one, and follow the steps. You will need your Social Security number and information about any current coverage.

You can also call 1-800-MEDICARE (1-800-633-4227). A representative can walk you through the process and answer questions about your specific situation. The line is open Monday through Friday, 8 a.m. to 8 p.m. Eastern time, and Saturday, 9 a.m. to 1 p.m.

A third option is to visit your local Social Security office in person. Bring your Social Security card, proof of citizenship or legal residency, and proof of age. You can find your nearest office at ssa.gov or by calling 1-800-772-1213.

What happens if you miss your enrollment window

If you do not enroll during your Initial Enrollment Period and you do not have creditable coverage, you will have to wait until the next General Enrollment Period. This runs from January 1 to March 31 each year, and coverage does not start until July 1 of that year. That means a gap of several months with no Part B coverage.

More importantly, you will owe a permanent penalty. Medicare adds 10 percent to your Part B premium for each full 12 months you were may be able to access but not enrolled. If you were may be able to access for three years before enrolling, your premium goes up 30 percent — and that increase stays in place for the rest of your life, even if you move to a different plan.

The only exceptions are if you have creditable coverage (employer or union insurance, TRICARE, or Veterans coverage) or if you are still working and covered by your employer's plan. If either applies to you, keep records proving it. You will need those records when you eventually enroll.

Part B costs and what is covered

Part B has a monthly premium, an annual deductible, and coinsurance. The premium amount changes each year and depends on your income — higher earners pay more. For 2024, the standard premium is $164.90 per month, but yours may be different. The annual deductible is $240, and after you meet it, you typically pay 20 percent of the cost of covered services.

Part B covers doctor visits, preventive care, lab tests, imaging, and durable medical equipment like wheelchairs and oxygen. It does not cover dental, vision, or hearing care. Many people add a Medigap or Medicare Advantage plan to cover costs Part B does not pay.

Frequently Asked Questions

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

You can still enroll in Part B during your Initial Enrollment Period even if you are working. If you have employer coverage, you can delay Part B without penalty as long as you enroll within eight months after that coverage ends. But if you have no other coverage, enroll during your Initial Enrollment Period to avoid the lifetime penalty.

Can I change my mind after I decline Part B?

Yes, but only during a General Enrollment Period (January 1 to March 31), and coverage will not start until July 1. If you declined because you had creditable coverage, you can enroll sooner during your Special Enrollment Period after that coverage ends. Bring proof of the coverage you had.

Do I need Part B if I have a Medicare Advantage plan?

Yes. Medicare Advantage (Part C) is an alternative way to get Part A and Part B coverage, but you must be enrolled in both Part A and Part B first. You cannot have Part C without Part B. If you choose Medicare Advantage, you still enroll in Part B during your Initial Enrollment Period.

What if I am on disability and turning 65?

If you have been receiving Social Security Disability Insurance (SSDI), you automatically become may be able to access for Medicare at 65. Your Initial Enrollment Period rules are the same as for anyone else. If you are already on Medicare because of disability, Part B enrollment happens automatically when you turn 65 unless you decline it.

Can I enroll in Part B after I have a health problem?

You can enroll during any General Enrollment Period (January through March), but coverage does not start until July. If you have a health problem and no coverage, you cannot wait for a special enrollment window — you should have enrolled during your Initial Enrollment Period. If you missed it, contact Medicare to ask about your options.