You enroll in Medicare Part B during a specific window, usually when you turn 65

Medicare Part B covers doctor visits, outpatient care, lab tests, and medical equipment. Unlike Part A (hospital insurance), which most people get automatically, you have to take a step to sign up for Part B. The standard time to enroll is during your Initial Enrollment Period, which runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after.

If you miss this window, you can still enroll later, but you may pay a permanent penalty on your monthly premium. The penalty is 10 percent of the standard Part B premium for each full year you delayed, and it stays with you for life. Because of this, the enrollment window matters — even if you do not need Part B right away, enrolling on time protects you from that cost.

Key Takeaways

  • You can enroll in Part B during the seven-month Initial Enrollment Period centered on your 65th birthday, or during the General Enrollment Period from January 1 to March 31 each year.
  • You enroll through Medicare.gov, by phone at 1-800-MEDICARE, by mail using Form CMS-40B, or in person at your local Social Security office.
  • Part B has a monthly premium (the amount varies by income and changes yearly), a yearly deductible, and a 20 percent coinsurance for most services after you meet the deductible.
  • If you delay enrollment past your Initial Enrollment Period without a valid reason, you will pay a permanent 10 percent penalty on your monthly premium for each year you waited.
  • If you are still working and have health insurance through your employer, you may be able to delay Part B without penalty under special rules called the Special Enrollment Period.

The three ways to enroll in Part B

The easiest route is online at Medicare.gov. Go to the "Sign Up for Medicare" section, create or log into your Medicare account, and follow the prompts. You will need your Social Security number and information about any current health coverage. The system will confirm your enrollment status right away.

If you prefer to speak with someone, call 1-800-MEDICARE (1-800-633-4227) and ask to enroll in Part B. Representatives are available Monday through Friday, 8 a.m. to 8 p.m. Eastern time, and they speak many languages. Have your Social Security number and any insurance information ready.

You can also enroll by mail using Form CMS-40B, which you can read from Medicare.gov or request by phone. Mail the completed form to your local Social Security office — the address is on the form itself. Processing by mail takes longer than online or phone enrollment, usually two to four weeks.

A fourth option is to visit your local Social Security office in person. Find the nearest office at ssa.gov/locator. Bring your Social Security card, proof of citizenship (passport, birth certificate, or naturalization papers), and proof of residency (utility bill or lease). Staff can enroll you on the spot.

What Part B costs and what it covers

Part B has three costs: a monthly premium, a yearly deductible, and coinsurance. The monthly premium amount changes each year and depends on your income — higher earners pay more. The standard premium in 2024 is $174.70 per month, but yours may be different based on your Modified Adjusted Gross Income from two years prior. Medicare sends you the exact amount in a notice each October.

The yearly deductible is $240 in 2024 (this amount changes yearly). Once you have paid that amount out of pocket for Part B services, your coinsurance kicks in. Coinsurance is usually 20 percent of the cost of a service after the deductible is met — you pay 20 percent, and Medicare pays 80 percent.

Part B covers doctor office visits, preventive care (like annual wellness visits and screenings), lab tests and X-rays, outpatient surgery, mental health services, and durable medical equipment like wheelchairs and oxygen. It does not cover routine dental, vision, or hearing care, or prescription drugs (that is Part D).

If you are still working: the Special Enrollment Period

If you are 65 or older but still working and covered by health insurance through your employer or your spouse's employer, you may not need to enroll in Part B right away. This is called creditable coverage, and it means your employer plan is at least as good as Part B.

Under the Special Enrollment Period, you can delay Part B without paying the permanent penalty — as long as you enroll within eight months of losing your employer coverage or retiring, whichever comes first. For example, if you retire at 67 and lose your employer plan, you have eight months to sign up for Part B without penalty.

To use this protection, you will need to prove you had creditable coverage. Your employer's benefits office can give you a letter stating the dates you were covered and confirming it was creditable. Keep this letter — you may need it if Medicare questions why you enrolled late.

What happens if you miss your enrollment window

If you do not enroll during your Initial Enrollment Period and you do not have a valid reason (like creditable employer coverage), you enter the General Enrollment Period. This runs from January 1 to March 31 each year, and coverage starts July 1 of that year. There is a gap — you are not covered for Part B between when you turn 65 and July 1.

More importantly, you will owe the permanent penalty. If you delayed two years, you pay 20 percent extra on your premium forever. If you delayed five years, you pay 50 percent extra forever. This penalty does not go away, even if you move to a different state or switch Medicare plans.

The only exceptions are if you had creditable coverage (employer insurance) or if you may have access to for a Special Enrollment Period for another reason — for instance, if you were living outside the United States when you turned 65. If you think you have a valid reason, contact Medicare at 1-800-MEDICARE to discuss it.

Coordinating Part B with other coverage

If you have a Medigap policy (supplemental insurance) or a Medicare Advantage plan, you still need Part B — it is the foundation. Medigap and Medicare Advantage both work alongside Part B. If you are switching from one to the other, you do not need to re-enroll in Part B itself.

If you have Veterans benefits or TRICARE (military health coverage), you can have both that coverage and Part B. They coordinate to cover your costs. Tell your VA or TRICARE provider that you have Medicare so they know how to bill.

If you have Medicaid (state health insurance for low-income people), Part B is separate. You can have both. In fact, Medicaid may help pay your Part B premium if your income is low enough. Contact your state Medicaid office to ask whether you may have access to for this help.

Frequently Asked Questions

What if I turn 65 but do not want Part B yet?

You can delay Part B if you have creditable coverage through an employer or spouse's employer. But if you do not have that coverage, you should enroll during your Initial Enrollment Period to avoid the permanent penalty, even if you do not plan to use it right away. The penalty is not worth the savings.

Can I enroll in Part B after I retire?

Yes, if you retire and lose your employer health insurance, you have eight months to enroll in Part B without penalty under the Special Enrollment Period. Contact Medicare as soon as you know your coverage will end so you can plan ahead.

Does Part B cover my prescriptions?

No. Part B covers doctor visits and medical services, but not prescription drugs. You need to enroll in Part D (prescription drug coverage) separately, usually during the same enrollment window as Part B. Part D is offered by private insurance companies, not Medicare directly.

What if I cannot afford the Part B premium?

If your income is low, you may may have access to for Extra Help or Medicaid, both of which can pay your Part B premium. Contact your state Medicaid office or call 1-800-MEDICARE to ask about programs in your state. You do not have to be enrolled in Medicaid to get help with Part B costs.

Do I have to enroll in Part B if I have Medicare Advantage?

Yes. Medicare Advantage is a way to receive your Part A and Part B benefits through a private plan, but you must be enrolled in both Part A and Part B first. You cannot have Medicare Advantage without Part B.