What Is Medicare Part B?
Medicare Part B is the "medical insurance" portion of Original Medicare. While Part A focuses on inpatient care, Part B covers outpatient services — everything from routine doctor visits to complex outpatient surgeries, preventive screenings, and the medical equipment you use at home. Unlike Part A, Part B is not free for most people: you pay a monthly premium regardless of whether you use it.
Part B is optional in the sense that you can choose not to enroll — but delaying without a qualifying reason results in a permanent late enrollment penalty of 10% per 12-month period you waited.
What Part B Covers
Doctor and Specialist Visits
Part B covers medically necessary visits to primary care doctors, specialists, and other healthcare providers who accept Medicare. This includes office visits, consultations, and follow-up appointments. After your annual deductible ($257 in 2025), you typically pay 20% of the Medicare-approved amount.
Outpatient Hospital Services
Services you receive at a hospital without being formally admitted as an inpatient are covered under Part B. This includes outpatient surgery, emergency department visits, and observation services. Note: if you're in the hospital under "observation status," you're covered by Part B — not Part A — which has different cost implications.
Preventive Services
One of Part B's most valuable features is its coverage of preventive services — many at $0 cost to you when your provider accepts Medicare assignment. Key preventive services include:
- Annual Wellness Visit (AWV)
- "Welcome to Medicare" preventive visit
- Mammograms (annually for women 40+)
- Colorectal cancer screenings
- Prostate cancer screening (PSA test)
- Cervical and vaginal cancer screenings
- Bone density measurements
- Diabetes screenings
- Flu shots (annually)
- Pneumococcal vaccines
- COVID-19 vaccines
- Hepatitis B vaccines
- Abdominal aortic aneurysm screening
- Depression screening
- Obesity screening and counseling
- Lung cancer screening (low-dose CT)
To get preventive services at $0 cost, your provider must accept Medicare assignment and you must not be receiving other services at the same visit that trigger cost-sharing.
Durable Medical Equipment (DME)
Part B covers medically necessary durable medical equipment prescribed by a doctor, including wheelchairs, walkers, hospital beds for home use, oxygen equipment, CPAP machines for sleep apnea, blood sugar monitors, and more. After the deductible, you typically pay 20% for DME from a Medicare-enrolled supplier.
Mental Health Services
Outpatient mental health services covered by Part B include visits to psychiatrists, psychologists, clinical social workers, and other mental health providers. Individual and group therapy sessions are covered. You pay 20% after the deductible (same as other Part B services).
Other Part B Services
- Lab tests, X-rays, and diagnostic imaging (MRI, CT scans)
- Ambulance services (when medically necessary)
- Second surgical opinions
- Outpatient physical, occupational, and speech therapy
- Cardiac rehabilitation programs
- Diabetes self-management training
- Kidney disease education
- Some home health care (overlaps with Part A)
- Clinical research studies
What Part B Does NOT Cover
- Routine dental exams, cleanings, fillings, or dentures
- Routine vision exams and most eyeglasses or contact lenses
- Hearing aids and routine hearing exams
- Most prescription drugs (covered by Part D)
- Cosmetic surgery
- Acupuncture (except for chronic low-back pain)
- Long-term custodial care
- Care received outside the U.S. (with few exceptions)
Part B Costs in 2025
| Cost Component | 2025 Amount |
|---|---|
| Standard monthly premium | $185.00 |
| Annual deductible | $257 |
| Coinsurance (after deductible) | 20% of Medicare-approved amount |
| Out-of-pocket maximum | None (Original Medicare alone has no cap) |
| Late enrollment penalty | 10% per 12-month period delayed (permanent) |
IRMAA: Higher Premiums for Higher Earners
If your income exceeds certain thresholds, you pay more than the standard Part B premium via the Income-Related Monthly Adjustment Amount (IRMAA). IRMAA is based on your income from 2 years prior (e.g., your 2025 premium is based on your 2023 tax return).
| Individual Income (2023) | Joint Income (2023) | 2025 Monthly Premium |
|---|---|---|
| ≤ $106,000 | ≤ $212,000 | $185.00 |
| $106,001 – $133,000 | $212,001 – $266,000 | $259.00 |
| $133,001 – $167,000 | $266,001 – $334,000 | $370.00 |
| $167,001 – $200,000 | $334,001 – $400,000 | $480.90 |
| $200,001 – $500,000 | $400,001 – $750,000 | $591.90 |
| Above $500,000 | Above $750,000 | $628.90 |
If your income has dropped significantly since 2023 (e.g., due to retirement), you can appeal your IRMAA determination using SSA Form SSA-44 (Life-Changing Event form).
Medicare Assignment — Why It Matters
When a doctor or provider "accepts Medicare assignment," they agree to accept Medicare's approved rate as full payment (beyond your deductible and 20% coinsurance). Most providers accept assignment.
If your provider does not accept assignment but is still enrolled in Medicare, they can charge up to 15% more than the Medicare-approved amount (called the "limiting charge"). If a provider has opted out of Medicare entirely, Medicare pays nothing — you pay the full bill.
Always confirm that your providers accept Medicare assignment before scheduling non-emergency care.