Medicare Part B Coverage — Physician Services, Outpatient Care, and the 20% Coinsurance Gap

Medicare Part B is the voluntary outpatient insurance program that covers the majority of your medical care outside a hospital stay — doctor visits, lab tests, imaging, outpatient surgery, physical therapy, preventive screenings, and durable medical equipment. Part B is voluntary in the sense that you must actively enroll (it doesn't happen automatically like Part A for most people), and you pay a monthly premium for it. The standard 2026 premium is $202.90/month (up from $185.00 in 2025), though higher-income enrollees pay significantly more through IRMAA surcharges. Once enrolled, Part B pays 80% of covered services after the annual deductible ($283 in 2026) — leaving you responsible for the other 20% with no annual cap. That uncapped 20% is the fundamental financial vulnerability of "original Medicare" without supplemental coverage: a $200,000 cancer treatment course leaves you with a $40,000 coinsurance obligation. Medigap plans (Medicare Supplement Insurance) and Medicare Advantage plans were both designed to address this gap.

Current Law (2026)

Legal Authority

• 42 U.S.C. § 1395j — Establishment: creates the "supplementary medical insurance program for aged and disabled" — the statutory foundation for Part B; characterizes it as voluntary insurance financed by enrollee premiums and federal contributions
• 42 U.S.C. § 1395k — Scope of benefits: enumerates covered services including medical and other health services, home health services, outpatient hospital services, and physician services; defines categories covered and categories excluded
• 42 U.S.C. § 1395l — Payment of benefits: establishes the 80%/20% cost-sharing structure and the annual deductible; provides the legal basis for coinsurance requirements
• 42 U.S.C. § 1395m — Special payment rules: covers specific payment methodologies for durable medical equipment, clinical laboratory tests, outpatient therapy services, imaging, and other specific service categories
• 42 U.S.C. § 1395y(a)(1)(A) — The "reasonable and necessary" exclusion: Medicare will not pay for items or services that are not reasonable and necessary for the diagnosis or treatment of illness or injury — the statutory basis for CMS coverage determinations and medical necessity reviews that lead to claim denials
• 42 U.S.C. § 1395y(b) — Medicare as secondary payer (MSP): establishes the conditions under which Medicare is the secondary rather than primary payer — including when an employer group health plan, workers' compensation plan, auto insurance, or liability insurance has primary responsibility

What Part B Covers

Part B covers a broad range of medically necessary outpatient and physician services:

Physician and clinical services: All services provided by physicians, nurse practitioners, physician assistants, clinical nurse specialists, certified nurse-midwives, and other licensed practitioners. This includes office visits, consultations, inpatient hospital visits (the physician fee component — the hospital facility is Part A), and telehealth services. Medicare pays physicians on the Medicare Physician Fee Schedule (MPFS), a relative value unit (RVU)-based system that is updated annually. Participating providers (those who accept Medicare assignment) cannot charge patients more than the Medicare-approved amount.

Outpatient hospital services: Services provided in a hospital outpatient department — outpatient surgery, emergency room visits, chemotherapy administered on an outpatient basis, radiation therapy, observation stays, and outpatient diagnostic procedures. Paid under the Outpatient Prospective Payment System (OPPS) using Ambulatory Payment Classifications (APCs).

Clinical laboratory and diagnostic tests: Blood tests, urinalysis, tissue pathology, Pap smears, and other clinical laboratory services are paid at 100% with no coinsurance when performed by a Medicare-certified laboratory. Imaging — X-rays, CT scans, MRI, nuclear medicine — is paid at the standard 80% after deductible.

Durable medical equipment (DME): Wheelchairs, walkers, crutches, home oxygen equipment, blood sugar monitors, CPAP machines, hospital beds, and other equipment that can withstand repeated use and is primarily used for a medical purpose. Medicare pays 80% of the approved amount; you pay 20% plus any difference if you use a non-participating supplier. For some DME categories (oxygen, wheelchairs, CPAP), CMS uses competitive bidding to set payment amounts.

Home health services: Skilled nursing care, physical therapy, speech therapy, occupational therapy, and home health aide services ordered by a physician and provided by a Medicare-certified home health agency — when the patient is homebound and requires skilled care. Home health is Part B for the home health agency visits themselves when not following a qualifying hospitalization (which would be Part A home health). There is no coinsurance for home health services, but there is a $50-per-episode copayment for some home health therapy.

Outpatient therapy: Physical therapy (PT), occupational therapy (OT), and speech-language pathology (SLP) services in an outpatient setting — covered at 80% after deductible. There are annual therapy caps, but exceptions apply for medically necessary services. As of 2022, the therapy cap exception process was made permanent under the Balanced Budget Act provisions.

Mental health services: Outpatient psychiatric and psychological services — including psychotherapy, depression screening, alcohol misuse counseling — covered at 80% after the Part B deductible, matching the rate for medical services. The Mental Health Parity and Addiction Equity Act and its Medicare extension ended the prior 50% coinsurance requirement for outpatient mental health.

Preventive services: A substantial array of preventive services are covered at 100% — no deductible, no coinsurance — when provided by a participating provider:

• Annual Wellness Visit (AWV): comprehensive health risk assessment, medical history review, personalized prevention plan
• Vaccinations: influenza, pneumococcal, COVID-19, hepatitis B
• Cancer screenings: colorectal (colonoscopy, stool tests), breast (mammogram annually for 40+), cervical (Pap/HPV), lung (CT scan for high-risk), prostate (PSA testing)
• Cardiovascular screening (lipid panel every 5 years)
• Diabetes screening and prevention programs
• Abdominal aortic aneurysm (one-time ultrasound for qualifying patients)
• Depression screening, alcohol misuse counseling, obesity counseling

Ambulance services: Ground and air ambulance transport to the nearest appropriate facility when other transportation would endanger the patient's health — 80% after deductible.

What Part B Does NOT Cover

Section 1395y(a) lists comprehensive exclusions from Medicare coverage. Significant gaps:

• Routine dental care: Fillings, extractions, dentures — not covered. Only dental services directly related to covered medical procedures (e.g., tooth extraction before heart valve surgery) may be covered in limited circumstances.
• Routine vision care: Eye exams for prescription glasses, glasses, or contact lenses — not covered. Exception: post-cataract surgery corrective lenses receive limited coverage.
• Routine hearing care: Hearing exams for fitting hearing aids, hearing aids themselves — not covered.
• Cosmetic surgery: Services for purely cosmetic purposes — not covered unless the condition results from accidental injury or improves the functioning of a malformed body part.
• Prescription drugs: Outpatient self-administered drugs are Part D, not Part B. Part B does cover some drugs administered in a clinical setting (IV chemotherapy, vaccines, some biologics given in a doctor's office).
• Custodial care: Long-term care services that are custodial (see Medicare Part A for hospital insurance coverage) (assistance with activities of daily living without requiring skilled medical care) — not covered by Part A or Part B.
• Care outside the United States: Coverage is generally limited to the United States and its territories, with narrow exceptions (emergency care near the Canadian or Mexican border, ship travel).
• Services not "reasonable and necessary": CMS uses National Coverage Determinations (NCDs) and Local Coverage Determinations (LCDs) to define what meets the standard; a service that doesn't meet the LCD/NCD criteria may be denied as not medically necessary.

The Advance Beneficiary Notice (ABN)

When a provider believes Medicare might deny a service as not medically necessary, they are required to give you an Advance Beneficiary Notice (ABN) before performing the service. The ABN informs you that Medicare may not pay and asks whether you still want the service. If you sign the ABN and Medicare denies the claim, you are responsible for the cost. If the provider doesn't give you an ABN before a service that Medicare later denies, the provider generally cannot bill you for it.

The ABN system protects beneficiaries from unexpected bills — it ensures you have informed consent about potential costs before receiving a service Medicare is unlikely to cover.

Medicare as Secondary Payer (MSP)

Medicare's secondary payer rules determine the order in which multiple health insurance policies pay:

• Active employees at employers with 20+ employees: Your employer group health plan pays first; Medicare pays second (only the amounts the group plan didn't cover). You cannot waive employer coverage to make Medicare primary — doing so violates the MSP rules.
• Disabled Medicare beneficiaries employed at firms with 100+ employees: Employer plan pays first for the first 30 months.
• End-stage renal disease (ESRD) patients: Employer plan pays first for the first 30 months after Medicare ESRD eligibility begins.
• Workers' compensation: Workers' compensation pays first for work-related injuries; Medicare pays for unrelated conditions.
• Auto/liability insurance: Conditional payments — Medicare may pay initially but must be reimbursed when a liability settlement is reached (the Medicare lien on tort settlements).

How It Affects You

If you're turning 65 soon: Enroll in Part B during your 8-month Initial Enrollment Period (starting the month you turn 65 or the month you stop working, whichever is later if you have employer coverage). Delaying enrollment without qualifying coverage — employer-sponsored insurance from active employment — results in a 10% premium penalty for every 12 months you delayed, which is permanent and compounds year after year. A two-year delay means a 20% higher premium for life.

If you're on original Medicare without supplemental coverage: The 20% coinsurance with no out-of-pocket cap is your single largest financial risk. A hospitalization (Part A) plus significant outpatient follow-up (Part B coinsurance on physician visits, physical therapy, imaging, outpatient surgery) can generate tens of thousands in unreimbursed costs. Consider a Medigap plan — particularly Plan G (covers all coinsurance except the Part B deductible) or Plan N (lower premium, small copays for office visits).

If you're still working at 65 with employer insurance: You don't have to enroll in Part B now. If your employer has 20+ employees and you're actively employed, your employer plan is primary. Delay Part B enrollment until you retire or lose employer coverage — you'll have an 8-month Special Enrollment Period to enroll without penalty.

If you receive a Part B denial: Request a redetermination from your Medicare Administrative Contractor (MAC) within 120 days of the denial. If denied again, escalate to a Qualified Independent Contractor (QIC) reconsideration, then to an Administrative Law Judge (ALJ) hearing. The appeals process has multiple levels and a meaningful success rate for medically necessary services that were denied based on documentation gaps rather than genuine exclusions.

If your income triggers IRMAA surcharges: Medicare Part B premiums are income-adjusted based on your Modified Adjusted Gross Income from two years prior — your 2024 MAGI determines your 2026 premium. The 2026 standard premium is $202.90/month, but single filers with 2024 MAGI over $109,000 face IRMAA surcharges that bring total Part B premium to a range of approximately $284.10 to $689.90/month at the highest brackets (single filers above ~$500,000; married filing jointly above ~$750,000 hit the top bracket). Married filers face double the income thresholds for the lower brackets. This creates a common surprise for two groups: retirees who sold a business, received a large capital gain, or did a large Roth conversion in a prior year (one-time income spikes carry forward two years into Medicare premiums); and high earners newly enrolling in Part B who haven't factored premium cost into their retirement budget. If your income has since dropped due to a "life-changing event" — retirement, divorce, death of a spouse, loss of income-producing property — file SSA Form SSA-44 to appeal. SSA will use more recent income rather than the two-year lookback, potentially cutting your surcharge significantly.

If you're transitioning from employer coverage to Medicare via COBRA: The single most expensive Medicare enrollment mistake is conflating COBRA with qualifying employer coverage. COBRA does not extend your Special Enrollment Period. Your 8-month SEP to enroll in Part B without penalty begins when active employment ends — not when COBRA ends. Example: you retire at 65 in January 2026 and take COBRA through July 2027 when it expires. You assume you can enroll in Medicare when COBRA runs out — but your SEP expired in September 2026 (8 months after retirement). You now owe a permanent 10% late enrollment penalty per year of delay, applied permanently to every future Part B premium. The rule: the moment you retire or lose active employer coverage, start the Medicare enrollment clock regardless of COBRA status. Enroll in Part B immediately when COBRA begins unless you have other qualifying active employer coverage (from a working spouse's employer with 20+ employees, for instance).

Implementing Regulations

• 42 CFR Part 410 — Supplementary Medical Insurance (Part B) Benefits (96 sections — the definitive coverage catalog for Medicare Part B, specifying which services are covered, the conditions they must meet, and any frequency or dollar limitations; works in conjunction with Part 411 exclusions and Part 414 payment rates). Key covered services and their conditions:

  • § 410.10 — Master included services list: physician services, outpatient hospital services, home health, clinical laboratory, durable medical equipment, ambulance, outpatient therapy (physical, occupational, speech), outpatient mental health, preventive services, and all other "medical and other health services" defined in § 1861(s) of the Social Security Act
  • § 410.16 — Initial preventive physical examination (IPPE or "Welcome to Medicare" exam): a comprehensive one-time preventive examination for Medicare beneficiaries within the first 12 months of Part B enrollment; includes health risk assessment, measurement of height/weight/BMI/blood pressure, electrocardiogram, hearing screening, and referrals for education or preventive services; covered at no cost-sharing (deductible and coinsurance waived)
  • § 410.15 — Annual Wellness Visit (AWV): available once per year (not in the same year as an IPPE); includes a Health Risk Assessment and Personalized Prevention Plan Services; covered at no cost-sharing; distinct from — and in addition to — a regular physician visit (which does require cost-sharing)
  • § 410.17 — Cardiovascular disease screening tests: covered once every 5 years without cost-sharing; includes tests for total cholesterol, HDL, LDL, and triglycerides; covered for beneficiaries at risk for cardiovascular disease or with no documented cholesterol measurement in the prior 5 years
  • § 410.18 — Diabetes screening tests: fasting glucose test and HbA1c covered annually for beneficiaries with risk factors (hypertension, dyslipidemia, obesity, prior gestational diabetes); covered at no cost-sharing
  • § 410.19 — Ultrasound screening for abdominal aortic aneurysm (AAA): one-time AAA screening covered for male beneficiaries 65-75 who have smoked at least 100 cigarettes, or for any beneficiary with a family history of AAA; covered at no cost-sharing
  • § 410.20 — Physician services: covered when furnished by an MD or DO; includes diagnosis and treatment, radiology, anesthesiology, surgery, psychiatric services, and services furnished in any setting where the beneficiary is enrolled in Part B; physician services are the largest Part B spending category
  • § 410.21 — Chiropractor limitations: Medicare covers chiropractic services only for manual manipulation of the spine to correct a subluxation that can be demonstrated by X-ray or physical examination; does not cover other diagnostic or therapeutic chiropractic services; chiropractors may not order laboratory tests, X-rays (for reimbursement beyond subluxation documentation), or other Part B services on behalf of Medicare patients
  • § 410.132 — Medical nutrition therapy (MNT): covered for beneficiaries with diabetes or renal disease; provided by registered dietitians or nutrition professionals; 3 hours/year initial, 2 hours/year subsequent referral (physician referral required); not covered for beneficiaries who receive MNT as part of a home health plan of care (which has its own benefit)
  • § 410.141 — Outpatient diabetes self-management training (DSMT): covered for beneficiaries with diabetes (any type); 10 hours initial training and 2 hours per year follow-up; must be a CMS-approved DSMT program; requires physician referral; important for newly diagnosed or poorly controlled diabetes
  • § 410.155 — Outpatient mental health treatment: in 2014, Congress eliminated the "50% limitation" (the historic requirement that Medicare pay only 50% of approved costs for outpatient mental health) — mental health services now receive the standard 80/20 cost-sharing (20% coinsurance after deductible), the same as other physician services; coverage includes psychiatry, clinical psychology, licensed clinical social worker, and clinical nurse specialist services

• 42 CFR Part 414 — Payment for Part B Medical and Other Health Services (197 sections across 18 subparts — the complete payment methodology for physician services, DME, drugs, ambulance, clinical lab, and all other Part B services):

  • Subpart B — Physicians and Other Practitioners (34s): the Medicare Physician Fee Schedule (MPFS) pays for every physician service using three components — (1) Relative Value Units (RVUs): a standardized measure of work effort, practice expense, and malpractice risk for each HCPCS/CPT procedure code (~10,000 codes); (2) Geographic Practice Cost Indices (GPCIs): locality-based adjusters for each RVU component, reflecting regional cost differences; (3) Conversion Factor (CF): a single dollar-per-RVU rate set annually (approximately $32–$33 in 2025–2026); payment formula: (Work RVU × Work GPCI + Practice Expense RVU × PE GPCI + Malpractice RVU × MP GPCI) × CF; the 2026 CF decreased ~2.9% absent congressional intervention (Congress partially patched the cut in the OBBBA package)
  • Subpart D — Durable Medical Equipment (DME) (15s): fee schedule for DME, prosthetics, orthotics, and supplies (DMEPOS); items classified as capped rental (wheelchairs, hospital beds — rented up to 13 months then ownership transfers), purchase, or inexpensive/routinely purchased; supplier accreditation required; competitive bidding areas (CBAs) override fee schedule in major metros (see Subpart F)
  • Subpart F — DMEPOS Competitive Bidding (18s): suppliers in CBAs submit bids for high-volume DMEPOS categories; CMS sets payment at winning bid rates; covers oxygen, CPAP/APAP, walkers, standard/power wheelchairs; beneficiaries in CBAs must use contract suppliers for these items; bidders must meet accreditation and financial standards
  • Subpart G — Clinical Diagnostic Laboratory Tests (10s): Clinical Laboratory Fee Schedule (CLFS) — laboratories paid at the lower of bill or fee schedule amount; Advanced Diagnostic Laboratory Tests (ADLTs — novel molecular pathology tests) paid at private payor median rate for three years then transitioned to CLFS; PAMA (Protecting Access to Medicare Act) requires labs to report private payor rates CMS uses to reset the schedule periodically
  • Subpart H — Ambulance Fee Schedule (8s): seven base rates by service level (BLS, ALS-1, ALS-2, Specialty Care Transport, Paramedic AIC, Fixed Wing, Rotary Wing); Geographic Adjustment Factor applied; rural areas receive 3% add-on; super rural ZIP codes receive additional 22.6% add-on; mileage payment per loaded mile; the "ambulance cliff" provisions that Congress repeatedly patches prevent deeper rural payment cuts
  • Subpart K — Drugs and Biologicals (14s): most Part B drugs paid at Average Sales Price (ASP) + 6% — ASP is the weighted average sales price across all purchasers net of discounts and rebates, calculated quarterly from mandatory manufacturer reports; biosimilars paid at reference product's ASP + 8% during initial period to incentivize adoption; Inflation Reduction Act authorized CMS to negotiate prices for certain high-cost Part B drugs beginning 2026
  • Subpart O — MIPS and APM Incentive Payment (36s — the Quality Payment Program core): MIPS adjusts physician fee schedule payments ±9% based on four performance categories: Quality (30%), Improvement Activities (15%), Promoting Interoperability/EHR use (25%), Cost/Resource Use (30%); clinicians below the performance threshold receive negative payment adjustments; exceptional performers receive positive adjustments; Advanced APM participants who meet patient/revenue volume thresholds are MIPS-exempt and receive a 3.5% APM Incentive Payment (scheduled to phase down); MIPS replaced the Sustainable Growth Rate (SGR) mechanism and three predecessor reporting programs (PQRS, Value Modifier, Meaningful Use) in 2017

• 42 CFR Part 415 — Services Furnished by Physicians in Providers, Supervising Physicians in Teaching Settings, and Residents in Certain Settings (30 sections — the rules that determine whether a physician who works at a hospital, teaching institution, or trains residents gets paid under the physician fee schedule or as part of the hospital's cost-based payment; this is the key regulatory distinction between a "private attending" and a "teaching physician" for Medicare billing). Key provisions:

  • § 415.102 — Conditions for fee schedule payment for physician services in providers: Medicare pays a physician at fee schedule rates — rather than bundling the payment into the hospital's rate — only if the physician bills for identified individual services (not just a time-based salary claim), has a separate agreement with the carrier, and the services are identifiable, billable professional services rather than administrative or supervisory time
  • § 415.110 — Medical direction of anesthesia: Medicare pays the physician for directing anesthesia services at fee schedule rates if the physician is involved in a single anesthesia case or concurrently directs 2–4 anesthesia procedures and personally performs specific "medically directing activities" (pre-anesthesia evaluation, prescribing the anesthesia plan, being present at induction and emergence, monitoring the course, being immediately available in the OR suite, providing post-anesthesia care); the fee schedule payment is 50% of the base rate per concurrently directed case for 2–4 concurrent cases
  • § 415.140 — Split (or shared) visits: when a physician and a non-physician practitioner (NP, PA) jointly provide an E/M service in a facility setting, Medicare pays at the physician rate if the physician performed the "substantive portion" — defined as more than half the total time, or the history, physical exam, or medical decision-making; effective January 1, 2024 the "substantive portion" is defined solely by time (more than 50% of total visit time); the billing practitioner is the practitioner present for the substantive portion
  • § 415.172 — Teaching physician presence requirement: Medicare pays a teaching physician the full physician fee schedule rate for services in a teaching setting only if the teaching physician was physically present during the key portion of the service and during any resident's portion of the service; "key portion" for surgical and procedural services means the critical or key portion of the procedure; for E/M services, the teaching physician must be present for the portion of the service that determines the level of the visit; the teaching physician's note must document their participation
  • § 415.174 — Primary care exception: in certain primary care residency programs (family medicine, general internal medicine, geriatrics, pediatrics, obstetrics/gynecology), a teaching physician may be paid for lower- and mid-level E/M services (99202–99203, 99212–99213) without being physically present during the resident's portion of the visit, if the teaching physician reviews the case with the resident immediately after the encounter; this exception is designed to support residency training in primary care while maintaining appropriate attending physician oversight
  • § 415.200 — Services of residents: a resident's professional services are never separately billable to Medicare — they are paid as part of the hospital's direct Graduate Medical Education (GME) payment; only the teaching physician or attending physician's separately documented services trigger a Part B fee schedule claim

  Part 415 governs a significant financial variable for academic medical centers and teaching hospitals: the rules determine when faculty physicians can bill Part B for their professional services vs. when those services are subsumed into the institution's cost-based payments. The distinction between a resident's service (non-billable) and a teaching physician's documented service (billable at fee schedule rates) is a major audit focus — Medicare Program Integrity contractors routinely review teaching hospital claims for compliance with the physical presence and documentation requirements. The split-visit substantive-portion change in 2024 (from a clinical-element definition to a time-based definition) was the most significant billing rule change for teaching hospitals and hospital-based practice groups in recent years.

• 42 CFR Part 411 — Exclusions From Medicare and Limitations on Medicare Payment (94 sections — the comprehensive list of what Medicare does NOT cover, organized as categorical exclusions and the general "reasonable and necessary" standard; also contains the Stark Law physician self-referral prohibition regulations). Key provisions:

  • § 411.15 — Specific statutory exclusions: dental services (except where dental procedure is performed incidentally to, and as an integral part of, a covered procedure — e.g., jaw reconstruction following accidental injury); foot care (routine foot care such as trimming nails and calluses — unless the beneficiary has a systemic condition that complicates routine foot care); hearing aids and routine hearing examinations; eyeglasses and routine vision examinations; orthopedic shoes (unless a shoe is an integral part of a leg brace); personal comfort items and services; cosmetic surgery (except when required for repair of accidental injury or to improve functioning of a malformed body part); services by an immediate relative or member of a household; services not within a practitioner's scope of license
  • § 411.20 — Limitation on payment for services not "reasonable and necessary": Medicare does not pay for "items or services... [that] are not reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member" (Social Security Act § 1862(a)(1)(A)); this is the most frequently litigated Medicare coverage standard — it is applied through Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs) that specify which diagnoses, patient populations, and clinical circumstances justify coverage; the Administrative Law Judge hearing system and Medicare Appeals Council adjudicate disputes over reasonable-and-necessary determinations
  • §§ 411.350–411.389 — Stark Law (physicians' referrals to entities with financial relationships): Part 411 Subpart J implements the Ethics in Patient Referrals Act (42 U.S.C. § 1395nn — "Stark Law"); a physician may not refer a Medicare patient for "designated health services" (DHS: clinical laboratory, physical and occupational therapy, radiology, radiation therapy, DME, parenteral/enteral nutrition, prosthetics/orthotics, home health, outpatient prescription drugs, inpatient/outpatient hospital services) to an entity with which the physician has a financial relationship, unless an exception applies; key exceptions include: in-office ancillary services provided within the physician's own practice (most significant), personal service arrangements (fair market value compensation), ownership of publicly traded securities, rural areas, and academic medical centers; violations result in claims not being paid and potential civil monetary penalties; Stark is a strict liability statute — no intent to violate is required for penalty exposure; the anti-kickback statute (which requires knowing and willful conduct) operates alongside Stark but requires intent

• 42 CFR Part 416 — Ambulatory Surgical Services (54 sections — the complete Medicare regulatory framework for ambulatory surgical centers, covering certification, conditions for coverage, and the ASC prospective payment system). Key provisions:

  • § 416.2 — Definition: an ASC is "any distinct entity that operates exclusively for the purpose of providing surgical services to patients not requiring hospitalization and whose expected stay does not exceed 24 hours"; this exclusivity requirement means a hospital's outpatient surgery department is not an ASC — it is paid under OPPS (Part 419), not the ASC payment system; the ASC definition is the gating requirement for the payment rate advantage
  • §§ 416.25–416.30 — Participation conditions: ASCs must have a signed agreement with CMS and meet all conditions for coverage in Subpart C; CMS may deem an accredited ASC (by Joint Commission, AAAHC, or AAAASF) to be in compliance with the conditions without a separate survey
  • Subpart C (§§ 416.40–416.75) — Conditions for coverage: 14 operational requirements covering governance (written policies and organized medical staff), patient rights (informed consent, medical records, patient privacy), infection prevention and control, quality assessment and performance improvement (QAPI), and physical environment requirements; state licensure is a prerequisite but does not substitute for federal conditions
  • §§ 416.160–416.178 — ASC Prospective Payment System (effective January 1, 2008): CMS pays ASC facility services at prospectively determined rates based on OPPS Ambulatory Payment Classification (APC) weights, scaled to the ASC payment level; the national unadjusted payment rate for each covered surgical procedure equals the OPPS APC payment rate × an ASC-to-OPPS conversion ratio (historically set to budget-neutrality) × a geographic wage adjustment; ASC rates are updated annually via notice-and-comment rulemaking published each November
  • § 416.164 — Scope of ASC services: covered surgical procedures are those specified on the ASC Covered Procedures List — maintained by CMS and updated annually; the list excludes procedures CMS determines are "typically only safely performed in an inpatient setting" due to clinical complexity or anesthesia duration; as of 2026, the ASC covered procedures list has expanded significantly under CMS's "site-neutral" initiative, including many procedures once restricted to hospital outpatient or inpatient settings
  • § 416.174 — Non-opioid pain management drugs: separate additional payment (beyond the packaged ASC rate) for qualifying non-opioid drugs and biologicals administered in the ASC to manage surgical pain — a payment incentive enacted to encourage opioid-sparing anesthesia protocols
  • §§ 416.300–416.310 — ASC Quality Reporting Program (ASCQR): ASCs that do not successfully participate in ASCQR receive a 2-percentage-point reduction in their annual payment update; quality measures collected include infection rates, safe surgery practices (pre-op antibiotic timing, surgical site identification), patient experience surveys, and claims-based measures; measure data is publicly reported on CMS's Care Compare tool

  The ASC payment system sits in a complex relationship with Medicare's hospital outpatient department (HOD) payment system. Many surgical procedures can be performed in either setting, but Medicare pays ASCs less than HODs for the same procedure — reflecting lower ASC overhead. As a result, patients pay lower coinsurance for the same surgery at an ASC than at a hospital outpatient department (20% of the lower ASC rate), which creates a financial incentive for ASC use when clinically appropriate. CMS's ongoing site-neutral payment initiative has further blurred the HOD/ASC distinction by moving more procedures to the ASC list and, separately, proposing to equalize payment rates for certain procedures regardless of setting — a policy change strongly opposed by hospital systems that rely on higher OPPS reimbursement.

• 42 CFR Part 419 — Prospective Payment Systems for Hospital Outpatient Department Services (35 sections — CMS rules implementing the Outpatient Prospective Payment System (OPPS), the payment methodology for hospital outpatient department services; effective August 1, 2000 under the Balanced Budget Refinement Act; the largest Medicare Part B payment system by spending after physician services):

  • § 419.2 — Unit of payment: OPPS pays hospitals a prospectively determined rate for each Ambulatory Payment Classification (APC) group rather than individual service items; an APC groups clinically similar services that require similar resources; a single hospital outpatient visit may involve multiple APCs (e.g., one APC for the procedure, one for drugs, one for radiology)
  • § 419.20 — Hospitals subject to OPPS: OPPS applies to participating hospital outpatient departments, community mental health centers (for partial hospitalization only), and certain Indian Health Service facilities; critical access hospitals (CAHs) are generally exempt from OPPS and paid under cost-based methodology
  • § 419.21 — Services subject to OPPS: covers hospital outpatient services generally, including surgical procedures, diagnostic imaging, emergency room services, observation services, outpatient chemotherapy and radiation therapy, and clinic visits; OPPS does NOT cover physician professional services performed in the outpatient department (those are paid under the Medicare Physician Fee Schedule)
  • § 419.22 — Services excluded from OPPS: certain services are carved out and paid separately — ambulance services (paid under ambulance fee schedule), clinical lab services (paid under CLFS), physical/occupational/speech therapy (paid under therapy fee schedules), and renal dialysis (paid under ESRD bundle)
  • § 419.31 — APC system and payment weights: CMS assigns every HCPCS code to an APC; each APC has a relative payment weight reflecting resource use; CMS updates APC assignments and weights annually through the Hospital Outpatient Prospective Payment System (OPPS) Annual Rule published each November and effective January 1; the annual rule also updates the national conversion factor ($/relative weight unit)
  • § 419.32 — Payment rate calculation: the payment rate for each APC = the APC's relative weight × the national conversion factor × the hospital's wage index adjustment for labor-related portions of the payment; hospitals in high-wage areas receive higher payments to account for higher staff costs; the wage index adjustment uses the same geographic areas as the inpatient PPS
  • § 419.41 — Beneficiary copayment: patients pay coinsurance on OPPS services; the statutory coinsurance is 20% of the national median charge (not 20% of the OPPS rate — a legal distinction that historically produced coinsurance amounts higher than 20% of the Medicare payment rate); CMS is working toward reducing statutory copayments to 20% of the OPPS payment rate; the annual OPPS rule includes coinsurance updates
  • § 419.43 — Quality adjustments: hospitals that fail the Hospital Outpatient Quality Reporting (OQR) Program requirements receive a 2-percentage-point reduction in their annual payment update; OQR requires hospitals to submit data on a CMS-specified set of quality measures covering safe surgery, infection prevention, stroke care, and patient experience; measure data is publicly reported on CMS's Care Compare tool
  • § 419.44 — Multiple procedure payment reductions: when multiple surgical procedures are performed in the same operative session, CMS reduces payment for the second and subsequent procedures by 50% — the rationale being that operating room setup, anesthesia, and recovery costs are shared across procedures and do not simply multiply per procedure

  The OPPS is updated annually through one of the most consequential healthcare rulemakings in the federal regulatory calendar. The annual OPPS/ASC Final Rule (published each November) determines how CMS will pay for approximately $90 billion in hospital outpatient services for the following year. Changes to APC assignments, conversion factor updates, new technology add-on payments, the packaging policy (which items are included in the APC bundled rate vs. paid separately), and the annual update to covered procedures for ASCs are all determined through this single rule. Hospital systems typically submit detailed comments during the proposed rule period (July-September each year) contesting proposed APC reassignments, conversion factor calculations, and packaging policy changes — making OPPS rulemaking one of the most heavily lobbied healthcare policy processes outside of Congressional action.

State Variations

Medicare Part B is a federal program with uniform national rules — states do not change Part B coverage, cost-sharing, or eligibility. However, states may:

• Require Medigap insurers to offer certain plan types (California, Massachusetts, and Minnesota have specific requirements)
• Fund state-based Medicare Savings Programs that pay Part B premiums for low-income beneficiaries (QMB, SLMB, QI programs) — reducing out-of-pocket costs for qualifying individuals
• Operate State Health Insurance Assistance Programs (SHIPs) that provide free counseling on Medicare options

Pending Legislation

• HR 2084 — Medicare and Medicaid Dental, Vision, and Hearing Benefit Act of 2025: would add dental, vision, and hearing benefits to traditional Medicare Part B and set a 90% Medicaid match for adult dental/vision/hearing services. Status: Introduced.
• HR 2329 — Medicare Orthotics and Prosthetics Patient-Centered Care Act: would tie Medicare payment for orthotics/prosthetics to patient training, curb drop shipments, expand practitioner exemptions, and require HHS to issue updated payment rules. Status: Introduced.
• HR 2066 — Medicare Transaction Fraud Prevention Act: would pilot predictive risk scores for Medicare DME and lab claims, using beneficiary opt-in and electronic alerts to flag suspicious payments. Status: Introduced.

The Build Back Better legislation (2021) included dental coverage for Medicare; the final Inflation Reduction Act (2022) did not. Drug price negotiation was enacted for Part D; similar cost-control provisions for Part B-administered drugs remain a policy discussion.

Recent Developments

The Inflation Reduction Act (2022) capped out-of-pocket costs for Part D prescription drugs (a major beneficiary protection for drugs administered outpatient under Part D) but did not add an out-of-pocket cap to Part B. CMS expanded telehealth coverage for Part B significantly during COVID-19, and many telehealth flexibilities were extended through 2024 and 2025. The 2024 Medicare physician fee schedule cut physician rates by approximately 3.4%, continuing the long-running tension between the fee schedule formula and adequate physician payment — Congress has historically intervened to prevent larger cuts under the Sustainable Growth Rate (SGR) and its successor, but the fundamental payment pressure remains. CMS finalized coverage for FDA-approved Alzheimer's drugs (lecanemab, donanemab) under Part B in 2024, subject to evidence development requirements.

• Alzheimer's drug coverage — lecanemab and donanemab (2024-2025): CMS's 2024 National Coverage Determination for amyloid-targeting Alzheimer's drugs (lecanemab/Leqembi, donanemab/Kisunla) finalized coverage under Part B for Medicare beneficiaries with early symptomatic Alzheimer's and confirmed amyloid pathology, conditioned on enrollment in a qualifying patient registry. The drugs cost approximately $26,500-$32,000 per year before Medicare; beneficiaries owe 20% coinsurance ($5,300-$6,400 annually), making supplemental coverage or Medigap critical. An estimated 1-2 million Medicare beneficiaries may be eligible, creating significant Part B cost implications as uptake grows.
• Telehealth permanence cliff — December 2026: Medicare telehealth flexibilities extended through COVID-19 and subsequent legislation expire December 31, 2026, unless Congress acts. The extensions allow audio-only telehealth, originating site waivers (allowing beneficiaries to receive telehealth from home rather than a medical facility), and expanded provider types (physical therapists, occupational therapists). If Congress does not act before the December 2026 deadline, an estimated 30 million Medicare telehealth visits per year would revert to in-person requirements. The OBBBA included a 2-year extension of telehealth provisions as part of its broader health provisions.
• IRA drug negotiation — Part B biologics next (2026-2027): After the first 10 negotiated drugs (primarily Part D) took effect January 1, 2026, CMS is required to select up to 15 Part B drugs for the 2027 negotiation cycle. Part B drugs — biologics administered in physician offices and outpatient settings — include expensive cancer drugs, autoimmune biologics, and ophthalmology drugs (anti-VEGF injections). Drugs selected for Part B negotiation will face Maximum Fair Prices beginning January 1, 2028. Oncologists and other physician-administered drug providers face potential revenue impact when their highest-cost infusion drugs come under negotiated pricing.
• Physician payment reform stalled, 2.9% cut in 2026: The Medicare physician fee schedule formula continues to produce annual cuts that Congress patches year-to-year but has never permanently fixed. The 2026 conversion factor decreased approximately 2.9% absent a legislative patch, reducing payments across all physician services. Congress passed a partial patch in late 2025 (as part of the OBBBA package) that limited but did not eliminate the cut. The American Medical Association and specialty societies have pushed for a permanent SGR-equivalent fix; the fundamental problem is that the fee schedule formula does not account for medical practice inflation, creating a structural underpayment that compounds each year.