Key Takeaways
- Medicare Part B covers outpatient services including doctor visits, lab work, and preventive care.
- Most enrollees pay a standard monthly premium for Part B, which is income-adjusted for higher earners.
- After the annual deductible, Part B generally pays 80% of approved costs — leaving you responsible for the remaining 20%.
- Many preventive services, such as annual wellness visits and certain screenings, are covered at no cost to you.
- Part B also covers durable medical equipment like wheelchairs and CPAP machines when deemed medically necessary.
- Late enrollment in Part B triggers a permanent premium penalty unless you have qualifying coverage elsewhere.
Medicare Part B
Medicare Part B is the part of Original Medicare that pays for outpatient medical care — think doctor visits, lab tests, mental health services, preventive screenings, and medically necessary equipment. Unlike Part A (which focuses on hospital stays), Part B covers the care you receive outside a hospital setting. Most people enrolled in Medicare need both Part A and Part B to have well-rounded coverage.
Part B is classified as "medical insurance" under the Social Security Act and is funded through monthly premiums paid by enrollees plus general federal revenue. Beneficiaries typically pay 20% of the Medicare-approved amount after meeting the annual deductible.
What Medicare Part B Is — and Why You Need It
When most people think of Medicare, they picture hospital coverage. But staying healthy involves a lot more than hospital stays. Every doctor visit, blood draw, X-ray, and annual checkup happens outside the hospital — and that's exactly where Medicare Part B steps in.
Part B is the "medical insurance" half of Original Medicare. Together, Part A (hospital insurance) and Part B form the foundation of Medicare coverage. Most people who qualify for Medicare need both parts, because they cover very different kinds of care. To understand how they divide responsibilities, see our comparison: Medicare Part A vs. Part B.
Part B is not free — it requires a monthly premium — but its coverage is broad and deeply valuable. Without it, routine medical care, specialist visits, diagnostic tests, and preventive screenings would all come entirely out of your own pocket.
For a complete picture of how all four Medicare parts — A, B, C, and D — work together, our guide to all Medicare parts is a good starting point.
What Part B Covers: The Two Main Categories
Part B coverage falls into two buckets: medically necessary services and preventive services. Knowing which bucket your care falls into matters — because the cost-sharing rules can differ significantly.
Medically Necessary Services
These are services or supplies your doctor determines are needed to diagnose or treat a medical condition. Medicare Part B pays 80% of the Medicare-approved amount for these services after you meet your annual deductible. You're responsible for the remaining 20% — with no out-of-pocket cap unless you have a Medigap or Medicare Advantage plan.
Common examples of medically necessary services covered under Part B include:
- Doctor office visits (primary care and specialists)
- Outpatient surgery and procedures
- Diagnostic imaging (X-rays, MRIs, CT scans)
- Laboratory and blood tests
- Mental health services (psychiatry, clinical psychology, counseling)
- Physical, occupational, and speech therapy
- Chemotherapy and radiation (in outpatient settings)
- Ambulance services when other transport would endanger health
- Second surgical opinions
- Emergency department visits
Watch for Billing Mix-Ups at the Doctor's Office
A common point of confusion: if you go in for a preventive visit but your doctor also addresses a new or existing medical problem during the same appointment, Medicare may split the billing. The preventive portion stays at $0, but the problem-focused portion may be billed as a separate medically necessary service — triggering your deductible and 20% coinsurance. Ask your doctor's office to clarify billing before combining visit types.
Preventive Services
Preventive services are the real hidden gem of Part B. When you receive a preventive service from a provider who accepts Medicare assignment, your cost is often $0 — no deductible, no coinsurance. This includes screenings, vaccines, and your Annual Wellness Visit.
Key preventive services covered at no cost include:
- Annual Wellness Visit and Welcome to Medicare preventive exam
- Cancer screenings (colorectal, breast, cervical, lung, prostate)
- Cardiovascular disease screening and risk counseling
- Diabetes screening and self-management training
- Vaccines (flu, hepatitis B, COVID-19, pneumococcal)
- Bone density measurements
- Depression and alcohol misuse screenings
For a complete list of zero-cost preventive services, see our detailed guide: Preventive Services Covered Under Medicare Part B.
Always Verify 'Medicare Assignment' Before a Visit
Before you schedule any appointment, ask your provider directly: 'Do you accept Medicare assignment?' Providers who accept assignment agree to charge no more than Medicare's approved rate, meaning you'll never owe more than your 20% share. Providers who don't accept assignment can legally charge up to 15% above the Medicare rate — and you're responsible for that extra amount.
Employer Coverage? You May Be Able to Delay Part B Safely
If you or your spouse is still actively working and covered by an employer group health plan with 20 or more employees, you can delay Part B enrollment without penalty. Make sure the coverage is through active employment — COBRA and retiree coverage do NOT count as qualifying coverage for this purpose. Enroll in Part B within 8 months of losing that employer coverage to avoid the late-enrollment penalty.
Durable Medical Equipment and Home Health Services
Part B also covers a category that surprises many beneficiaries: durable medical equipment (DME). If your doctor determines that a piece of equipment is medically necessary for home use, Part B will pay 80% of the approved cost after your deductible.
Covered DME includes:
- Wheelchairs and walkers
- CPAP and BiPAP machines for sleep apnea
- Hospital beds for home use
- Oxygen equipment and supplies
- Blood glucose monitors and test strips (for people with diabetes)
- Nebulizers for asthma or COPD
Equipment must be prescribed by a Medicare-enrolled physician, and you must use a Medicare-approved supplier. Using an out-of-network supplier can mean paying the full cost yourself.
Part B also covers some home health services — but only under specific conditions. You must be homebound, require skilled nursing care or therapy, and have a physician certify the need. These services are covered at 100% with no deductible, though you pay 20% for durable medical equipment used during home health care. Note that custodial care (help with bathing, dressing, or cooking) is not covered under Part B.
What Part B Does NOT Cover
Part B is broad, but it has clear gaps. Understanding what's excluded helps you avoid unexpected bills and plan for supplemental coverage if needed.
| Not Covered by Part B | Where to Look Instead |
|---|---|
| Prescription drugs (most outpatient) | Medicare Part D |
| Routine dental care (cleanings, fillings, dentures) | Standalone dental plan or Medicare Advantage |
| Routine vision exams and eyeglasses | Standalone vision plan or Medicare Advantage |
| Hearing aids and routine hearing exams | Medicare Advantage plans (some) |
| Long-term custodial care | Long-term care insurance |
| Cosmetic surgery | Not typically insurable |
| Care received outside the U.S. | Travel health insurance or Medigap Plan C/D/F/G |
| Acupuncture (except for low back pain) | Medicare Advantage or out-of-pocket |
The 20% coinsurance with no cap is the most significant financial risk under Part B. If you're managing a serious illness requiring frequent specialist care, that 20% can add up fast. This is a key reason many enrollees pair Part B with either a Medigap supplemental plan or a Medicare Advantage (Part C) plan.
“The 20% coinsurance under Medicare Part B sounds modest until you're facing cancer treatment or a serious surgery. Without a cap on out-of-pocket spending, that 20% can easily reach tens of thousands of dollars in a single year — which is exactly why supplemental coverage decisions matter so much.”
— Tricia Neuman, Senior Vice President, Kaiser Family Foundation, Medicare Policy Expert
What You'll Pay: Premiums, Deductibles, and Coinsurance
Let's be concrete about costs. Part B isn't free, and the expense structure involves three layers you should know before enrolling.
Monthly Premium
Most people pay the standard premium, which is $174.70 per month in 2024. However, if your income exceeds certain thresholds (based on your tax return from two years prior), you'll pay a higher premium called IRMAA — the Income-Related Monthly Adjustment Amount. In 2024, IRMAA surcharges range from an extra $69.90/month to an extra $419.30/month depending on income.
Annual Deductible
Before Part B kicks in, you must meet your annual deductible — $240 in 2024. This applies only to medically necessary services, not to most preventive care.
Coinsurance: The 80/20 Split
After your deductible, Part B pays 80% of the Medicare-approved amount for covered services. You pay the remaining 20%. There is no out-of-pocket maximum under Original Medicare alone — which is why supplemental coverage is worth considering.
$174.70
Standard monthly Part B premium (2024)
Per the Centers for Medicare & Medicaid Services (CMS); higher-income enrollees pay more through IRMAA surcharges.
$240
Annual Part B deductible (2024)
Applies to medically necessary services; most preventive care has no deductible requirement.
20%
Your share after Part B pays 80%
There is no out-of-pocket cap under Original Medicare Part B, making this coinsurance a key financial risk.
66 million+
Americans enrolled in Medicare Part B
According to CMS enrollment data, the vast majority of Medicare beneficiaries carry Part B coverage.
10%
Late enrollment penalty per year missed
This penalty is permanent and added to your monthly Part B premium for as long as you remain enrolled.
For a full table of 2024 Part B costs alongside Parts A, C, and D, visit our Medicare costs at a glance reference. And if you want help understanding how deductibles generally work across insurance types, see our primer on premiums and deductibles.
Enrollment: When to Sign Up and What Happens If You Wait
Timing your Part B enrollment correctly is one of the most important Medicare decisions you'll make. Mess it up, and you could pay more every month for the rest of your life.
Initial Enrollment Period (IEP)
You have a 7-month window to enroll in Part B: the 3 months before the month you turn 65, the month of your birthday, and the 3 months after. If you're already receiving Social Security, you're automatically enrolled — you'll receive your red, white, and blue Medicare card in the mail.
Special Enrollment Period (SEP)
If you're still working at 65 and covered by an employer group health plan (through your own or a spouse's active employment), you can delay Part B without penalty. You'll get a Special Enrollment Period when that employer coverage ends: 8 months to sign up without a late penalty.
The Late Enrollment Penalty
If you miss your enrollment window without qualifying coverage, Medicare adds a 10% premium penalty for each full 12-month period you were eligible but didn't sign up. That penalty is permanent — it follows you for life. On the 2024 standard premium of $174.70, even a one-year delay costs an extra $17.47 per month, every month, forever.
Always Verify 'Medicare Assignment' Before a Visit
Before you schedule any appointment, ask your provider directly: 'Do you accept Medicare assignment?' Providers who accept assignment agree to charge no more than Medicare's approved rate, meaning you'll never owe more than your 20% share. Providers who don't accept assignment can legally charge up to 15% above the Medicare rate — and you're responsible for that extra amount.
Employer Coverage? You May Be Able to Delay Part B Safely
If you or your spouse is still actively working and covered by an employer group health plan with 20 or more employees, you can delay Part B enrollment without penalty. Make sure the coverage is through active employment — COBRA and retiree coverage do NOT count as qualifying coverage for this purpose. Enroll in Part B within 8 months of losing that employer coverage to avoid the late-enrollment penalty.
General Enrollment Period (GEP)
If you miss your IEP and don't qualify for an SEP, you can enroll during the General Enrollment Period: January 1 through March 31 each year, with coverage beginning July 1. The late-enrollment penalty still applies.
How to Get More From Your Part B Coverage
Many Part B enrollees leave real value on the table simply because they don't know what they're entitled to. Here are practical ways to use your benefits fully.
Use Your Annual Wellness Visit
Once you've been enrolled in Part B for 12 months, you're eligible for a free Annual Wellness Visit (AWV) every year. This isn't a physical exam in the traditional sense — it's a personalized health review where your doctor updates your health history, screens for cognitive impairment, and builds a prevention plan. It costs you nothing if your provider accepts Medicare assignment.
Know the "Welcome to Medicare" Visit
Within your first 12 months of Part B enrollment, you can schedule a one-time "Welcome to Medicare" preventive visit. It's free, and it's different from your annual wellness visit. Don't skip it — it sets a baseline for your care going forward.
Confirm Your Provider Accepts Medicare Assignment
When a provider "accepts assignment," they agree to accept Medicare's approved amount as full payment. If your doctor doesn't accept assignment, they can charge up to 15% above the Medicare-approved rate (the "limiting charge") — and you're responsible for that difference. Always ask before scheduling: "Do you accept Medicare assignment?"
For a detailed strategy guide on maximizing your Part B benefits, see: Making the Most of Medicare Part B's Benefits.
Part B in the Bigger Medicare Picture
Part B doesn't exist in isolation. It's one piece of a coverage structure that most beneficiaries need to think about holistically.
Part A + Part B = Original Medicare. This is the foundation. Most people enroll in both when they turn 65. Original Medicare covers a wide range of services, but it comes with cost-sharing gaps — particularly the 20% coinsurance with no maximum.
Part C (Medicare Advantage) is an alternative way to receive your Part A and B benefits through a private insurer. These plans often include extra benefits (dental, vision, hearing) and may cap your out-of-pocket costs. But they also use networks, which means your doctor choices may be restricted.
Part D covers prescription drugs and is a separate enrollment from Part B. If you rely on outpatient medications (and most people do), Part D is critical.
Medigap (Medicare Supplement Insurance) can fill in Part B's gaps — particularly that 20% coinsurance — but it requires paying an additional monthly premium on top of Part B.
The right combination depends on your health needs, budget, and where you live. What matters first is understanding what Part B itself provides — and now you do. The full Medicare parts guide can help you see how everything fits together.
Frequently Asked Questions
All claims in this article are backed by peer-reviewed research. We follow strict editorial guidelines to ensure accuracy and reliability. Sources available on request from our editorial team.
