Overview: Part B is the outpatient half of Original Medicare, covering physician services, preventive care, and a wide range of medically necessary services delivered outside a hospital inpatient stay.

What Part B Covers

Part B covers two broad categories:

Medically necessary services include doctor and specialist visits, outpatient hospital care, diagnostic tests (lab work, X-rays, MRIs), durable medical equipment (wheelchairs, walkers, oxygen), mental health services, ambulance transportation, and certain drugs administered by a provider in an outpatient setting (like chemotherapy or injected medications). Notably, physician services received while in the hospital are also billed under Part B, not Part A.

Preventive services include the one-time "Welcome to Medicare" visit, annual wellness visits, cancer screenings (mammograms, colonoscopies, prostate and cervical cancer screenings), cardiovascular screenings, diabetes screenings and self-management training, immunizations (flu, pneumococcal, COVID-19, hepatitis B), depression and substance use screenings, and bone mass measurements for high-risk individuals. Most preventive services have $0 cost-sharing when received from a provider who accepts Medicare assignment.

Part B Cost-Sharing (2026)

Standard monthly premium: $202.90
Annual deductible: $283
Coinsurance: 20% of the Medicare-approved amount for most covered services after the deductible is met; Medicare pays the remaining 80%

A critical point for the exam: Original Medicare Part B has no annual out-of-pocket maximum. The 20% coinsurance accumulates without a ceiling, meaning a catastrophically expensive year of care — say, extensive chemotherapy — can produce an unlimited personal obligation. This structural gap is the primary reason beneficiaries purchase Medigap supplemental insurance or enroll in Medicare Advantage.