Part B is the medical insurance piece of Original Medicare

Part B covers doctor visits, outpatient care, lab tests, imaging, and preventive services when you see providers who accept Medicare. It is separate from Part A (hospital insurance) and works alongside it. You pay a monthly premium for Part B, and you also pay a share of the cost when you use a service — typically 20 percent of what Medicare approves after you meet your deductible.

Part B is optional, but most people who have Part A end up taking it. If you delay signing up without a valid reason, you may face a permanent penalty on your premium. The standard monthly premium changes each year; in 2024 it was $164.90 for most people, though higher earners pay more.

Part B is run by the Centers for Medicare & Medicaid Services (CMS), the federal agency that administers Medicare. You do not choose a separate company for Part B the way you might for a Medigap or Medicare Advantage plan — it is the same benefit structure for everyone.

Key Takeaways

  • Part B covers doctor office visits, lab work, imaging, outpatient surgery, and preventive care like screenings and vaccines when you see a Medicare-accepting provider.
  • You pay a monthly premium (which varies by income), a yearly deductible (usually around $240), and then 20 percent of the approved cost for most services.
  • Part B does not cover routine dental, vision, or hearing care, or prescription drugs — those require separate coverage or out-of-pocket payment.
  • If you turn 65 and do not sign up for Part B when you first become may be able to access, you will pay a higher premium for as long as you have Medicare.

What Part B actually pays for

Part B covers visits to your doctor, whether for a regular checkup, a chronic condition, or an acute problem. It pays for lab tests ordered by your doctor, X-rays, ultrasounds, CT scans, and other imaging. It covers outpatient procedures — things done in a hospital or surgery center where you go home the same day. It also covers mental health visits, physical therapy, occupational therapy, and speech therapy when medically necessary.

Preventive services are covered at no cost to you: annual wellness visits, cancer screenings (mammograms, colonoscopies, Pap smears), cardiovascular screenings, diabetes screenings, bone density tests, and vaccines like flu and pneumonia shots. You do not pay the deductible or coinsurance for these preventive visits if you see a provider who accepts Medicare assignment.

Part B also covers durable medical equipment — wheelchairs, walkers, oxygen equipment, diabetic supplies — though you typically pay 20 percent after the deductible. It covers some home health services ordered by your doctor, and it covers ambulance transport when medically necessary.

What Part B does not cover

Part B does not pay for routine dental work, dentures, dental implants, or tooth extractions. It does not cover routine eye exams, eyeglasses, or contact lenses. It does not cover hearing aids or routine hearing exams. These are common gaps that catch people off guard, and you will need to pay out of pocket or buy separate coverage.

Part B does not cover prescription drugs. That is what Part D is for — a separate drug plan you choose and pay for. Part B also does not cover long-term care, custodial care in a nursing home, or most care in an assisted living facility. It does not cover cosmetic surgery, and it does not cover most services from providers outside the United States.

Routine foot care, routine physical exams for work or sports, and most weight-loss programs are not covered. Neither is acupuncture, except in limited circumstances for chronic lower back pain.

How much you pay: premiums, deductibles, and coinsurance

The monthly premium for Part B in 2024 was $164.90 for most people, but it changes each year. If your modified adjusted gross income is above a certain threshold (in 2024, above $97,000 for a single filer), you pay a higher premium — sometimes significantly higher. The income thresholds and surcharge amounts change annually.

Once you have Part B, you also have an annual deductible. In 2024 it was $240. You pay this deductible once per year before Medicare starts paying its share. After you meet the deductible, Medicare typically pays 80 percent of the approved cost for most services, and you pay 20 percent. For some services like mental health visits, the split is the same. For preventive services with no deductible or coinsurance, you pay nothing.

The amounts change each year. Your provider must accept Medicare assignment (agree to accept Medicare's approved amount as payment in full) for these cost-sharing rules to explore. If a provider does not accept assignment, you may owe more.

When to sign up and what happens if you miss the important date

You become may be able to access for Medicare at 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. If you sign up during this window, your Part B coverage starts the month you turn 65 (or the first of the month after you turn 65, depending on when you sign up).

If you miss this window and do not have other health coverage, you will pay a permanent penalty. The penalty is 10 percent of the standard premium for each full year you were may be able to access but not signed up. If you were may be able to access for eight years and did not sign up, you would pay 80 percent more than the standard premium for the rest of your life. This penalty does not go away.

There are exceptions: if you were covered by a group health plan through your job or your spouse's job, or if you were covered by TRICARE or the Veterans Administration, you may have a special enrollment period that lets you sign up without penalty. You must sign up within eight months of losing that coverage.

Part B versus Medicare Advantage and Medigap

Part B is the foundation of Original Medicare. You can use it as-is, pay out of pocket for what it does not cover, and buy a Medigap plan to fill the gaps. Or you can switch to a Medicare Advantage plan (Part C), which is an alternative to Original Medicare run by a private insurance company. Medicare Advantage usually has lower or no premiums, but it comes with a network, prior authorization requirements, and different cost-sharing rules.

If you stay on Original Medicare (Part A and Part B), you can see any provider who accepts Medicare anywhere in the country. You have no network restrictions. But you are responsible for the 20 percent coinsurance on most services, and you have no cap on out-of-pocket costs unless you buy a Medigap plan. Medigap plans are sold by private insurers and help pay the costs that Original Medicare does not cover.

The choice between Original Medicare with Medigap and Medicare Advantage depends on your health, your budget, and which doctors you want to see. There is no single right answer.

How to enroll in Part B

You can sign up for Part B online through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office. You will need your Social Security number and proof of citizenship or legal residency. If you are signing up during your initial enrollment period, the process is straightforward and takes about 15 minutes online.

If you are signing up late and believe you have a valid reason (such as continuous coverage through an employer), you will need to provide documentation of that coverage. Social Security will review your case to determine whether you owe a penalty.

Once you are enrolled, you will receive a Medicare card in the mail. Part B coverage typically starts the first of the month after you sign up, though it can start earlier depending on when you enroll.

Frequently Asked Questions

Do I have to take Part B if I have Part A?

Part B is optional, but if you do not sign up when you first become may be able to access and you do not have other health coverage, you will pay a permanent 10 percent penalty on your premium for each year you were may be able to access but not enrolled. Most people find it worth taking Part B to avoid this penalty.

What if I am still working at 65 — do I still need Part B?

If you or your spouse are still working and covered by a group health plan, you can delay Part B without penalty. You have eight months after your coverage ends to sign up. You will need to provide proof of your group coverage when you enroll.

Does Part B cover my doctor's office copay?

Part B does not use copays the way commercial insurance does. Instead, you pay 20 percent of the Medicare-approved amount after you meet your annual deductible. Your doctor's office may call this an "estimated patient responsibility" or "coinsurance." The exact amount depends on the service and the approved cost.

Can I use Part B outside the United States?

Part B generally does not cover care outside the U.S., with rare exceptions for emergency care in Canada or Mexico near the U.S. border. If you travel internationally, you may want to buy supplemental travel insurance or a Medigap plan that covers emergency care abroad.

What is the difference between Part B and Part D?

Part B covers doctor visits, lab work, and medical equipment. Part D covers prescription drugs. They are separate plans with separate premiums and deductibles. You choose a Part D plan from private insurers; Part B is the same for everyone.