What Is Medicare Part B? Medical Coverage Explained

While Medicare Part A handles your hospital bills, Medicare Part B is what covers you the rest of the time — doctor visits, outpatient procedures, lab work, preventive care, and much of the medical equipment you might need at home. Understanding Part B's structure is essential for anyone on Medicare or approaching 65.

What Does Medicare Part B Cover?

Medicare Part B covers two broad categories:

Medically necessary services: Anything your doctor or other healthcare provider orders to diagnose or treat a medical condition. This includes:

• Physician office visits and consultations
• Outpatient hospital services and surgery
• Mental health services (therapy, psychiatry)
• Ambulance services
• Clinical laboratory tests (blood work, urinalysis)
• Diagnostic imaging (X-rays, MRIs, CT scans)
• Physical, occupational, and speech therapy
• Chemotherapy and radiation (outpatient)
• Dialysis
• Durable medical equipment (DME): wheelchairs, hospital beds, oxygen equipment, continuous glucose monitors

Preventive services: Part B covers a wide range of preventive screenings and vaccinations at no cost (no deductible, no coinsurance), including:

• Annual wellness visits
• Cancer screenings (colonoscopy, mammogram, Pap smear, lung cancer screening)
• Cardiovascular disease screenings
• Diabetes screening and self-management training
• Depression screening
• Vaccinations (flu, hepatitis B, pneumococcal)

Part B Premiums

Unlike Part A, everyone on Medicare Part B pays a monthly premium. For 2025:

Standard premium: $185.00/month

Higher-income beneficiaries pay more through Income-Related Monthly Adjustment Amounts (IRMAA). For 2025:

• $106,000–$133,000 (single) / $212,000–$266,000 (joint): $259.00/month
• $133,000–$167,000 / $266,000–$334,000: $370.00/month
• $167,000–$200,000 / $334,000–$400,000: $480.90/month
• $200,000–$500,000 / $400,000–$750,000: $591.90/month
• Above $500,000 / $750,000: $628.90/month

IRMAA is based on your income from two years prior. If your income dropped significantly (retirement, life event), you can request a reconsideration of IRMAA using SSA Form SSA-44.

Part B Deductible and Coinsurance

Annual deductible: $257 (2025) — paid once per calendar year, after which Part B begins sharing costs.

Coinsurance: After the deductible, you typically pay 20% of the Medicare-approved amount for most Part B services. Medicare pays 80%.

This 20% coinsurance has no cap unless you have supplemental coverage (Medigap or Medicaid) or a Medicare Advantage plan. A very expensive outpatient procedure or ongoing therapy can expose you to significant cost-sharing under Part B alone.

Part B Excess Charges

Doctors who accept Medicare must either:

• Accept Medicare assignment (agreeing to accept Medicare's approved amount as full payment), or
• Be "non-participating" (can charge up to 15% above Medicare's approved amount — called excess charges)

Some states prohibit excess charges. If your doctor charges excess amounts and you have a Medigap Plan G or F, those excess charges are covered by your supplement.

If you're billed more than 15% above Medicare's approved amount, that's illegal — report it to Medicare.

Prior Authorization Denied: How to Appeal" class="auto-link">Prior Authorization for Part B

Original Medicare generally does not require prior authorization for most physician services. However, CMS has been expanding prior authorization requirements for certain high-cost services, including:

• Non-emergent hyperbaric oxygen therapy
• Certain durable medical equipment (power wheelchairs, CPAP machines)
• Botulinum toxin injections
• Some outpatient hospital services

If your Medicare-approved item requires prior authorization and it wasn't obtained, the claim can be denied.

Common Medicare Part B Denials

1. Service not medically necessary. The most frequent denial reason. Medicare uses Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs) to define when services are covered. If your clinical documentation doesn't support the diagnosis or indication listed in the applicable policy, the claim is denied.

2. Duplicate claim. Medicare won't pay for the same service billed twice. Check whether your provider submitted a corrected claim.

3. Coverage excluded by statute. Certain services are categorically excluded from Part B: routine dental care, routine vision, hearing aids, most chiropractic beyond spinal manipulation, and cosmetic surgery.

4. DME denial. Durable medical equipment claims are frequently denied due to incomplete documentation — the physician's order didn't include required elements, the diagnosis doesn't match, or the equipment category requires prior authorization.

5. Part B drug coverage issues. Some drugs are covered under Part B (chemotherapy administered in an office, injectable drugs given by a provider) rather than Part D. Billing under the wrong part, or using a non-assigned pharmacy, can lead to denial.

Appealing Part B Denials

The Medicare appeals process applies to Part B denials:

Level 1: Redetermination — file within 120 days of the Medicare Summary Notice (MSN) date.

Level 2: Qualified Independent Contractor (QIC) Reconsideration — file within 180 days of Level 1 decision.

Level 3: ALJ Hearing — requires $190 minimum in dispute, file within 60 days.

Level 4: Medicare Appeals Council — within 60 days.

Level 5: Federal Court — requires statutory minimum.

For DME denials specifically, your supplier must give you an Advance Beneficiary Notice (ABN) if they believe Medicare won't pay. This notice lets you decide whether to proceed and be responsible for the cost. If they didn't give you an ABN and Medicare denied the claim, you may not owe anything.

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Related Reading:

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs External Insurance Appeal