What Is Medicare Billing?
Medicare billing submits claims to one of 12 regional Medicare Administrative Contractors (MACs) that adjudicate Part A institutional claims (UB-04) and Part B professional claims (CMS-1500). Compliance hinges on national NCD policy, regional LCD policy, ABN documentation for non-covered services, and a 365-day timely-filing window from the date of service.
- MAC jurisdiction: claims submitted to the regional Medicare Administrative Contractor for the rendering location
- Part A: institutional billing on UB-04. Part B: professional billing on CMS-1500
- LCD/NCD compliance plus ABN (Form CMS-R-131) required for non-covered services
- Timely filing: 365 days from date of service per 42 CFR 424.44
Medicare Billing Services
An eight-provider internal medicine group with 5,400 traditional Medicare encounters a year typically routes claims to a single Medicare Administrative Contractor (MAC), which means one set of LCD policies governs documentation rules — until that group adds a satellite office across a state line and suddenly every claim from the new location needs to clear a different MAC's coverage determinations. That is the working baseline of Medicare billing: a federal program where Part A institutional claims travel on UB-04, Part B professional claims on CMS-1500, the timely-filing window is fixed at 365 days from date of service per CMS regulation 42 CFR 424.44, and the 12 Medicare Administrative Contractors that adjudicate claims each publish supplementary coverage rules that frequently diverge from one another. This page covers how Medicare billing actually plays out across MAC routing, ABN documentation under §1879 of the Social Security Act, LCD/NCD compliance, Medicare Secondary Payer (MSP) coordination, QMB crossover claims to state Medicaid programs, and the operational discipline that keeps clean-claim rates above 95% on a payer that processes roughly 1.4 billion claims a year.
Medicare at a Glance
U.S. Medicare-eligible population
65+ million
Source: CMS Office of the Actuary, public
Americans aging into Medicare daily
~10,000
Source: Social Security Administration, public
Standard Medicare timely filing
365 days from DOS
Source: 42 CFR 424.44, public
Part A/B claims processed annually
~1.4 billion
Source: CMS, public
Number of MAC jurisdictions
12 A/B MACs nationwide
Source: CMS, public
Average clean-claim adjudication
14 days (electronic)
Source: CMS Medicare Claims Processing Manual, public
Billing Challenges Specific to Medicare
MAC jurisdiction routing — different rules by region
Medicare claims route to one of 12 A/B Medicare Administrative Contractors based on the rendering provider's state. Each MAC publishes its own Local Coverage Determinations (LCDs) that supplement national CMS policy. Novitas Solutions covers a different policy footprint than Noridian or Palmetto GBA, so a multi-state group with providers in two MAC jurisdictions must apply different documentation standards per claim depending on where the service was rendered. A skin-lesion destruction claim that clears one MAC's LCD on documented size and morphology can deny under another MAC's LCD that requires explicit pathology correlation.
ABN (Advance Beneficiary Notice) discipline for non-covered services
When a clinician provides a service Medicare is likely to deem not reasonable and necessary under §1862(a)(1) of the Social Security Act, the patient must sign Form CMS-R-131 (the ABN) before the service is rendered. The claim is then submitted with modifier GA (waiver of liability on file), GX (voluntary ABN), GY (statutorily excluded — no ABN required), or GZ (expected denial, no ABN obtained). A missing or improperly executed ABN means the practice cannot bill the patient for the denied service. Practices that do not standardize ABN workflows around medically necessary frequency limits — colonoscopies, EKGs, Vitamin D testing — write off services they could have collected on.
LCD/NCD compliance and medical-necessity documentation
National Coverage Determinations (NCDs) bind every MAC; Local Coverage Determinations (LCDs) bind only the issuing MAC's jurisdiction. Both publish covered ICD-10 lists and required documentation elements for services like sleep studies (NCD 240.4), continuous glucose monitors (LCD L33822 series), and home oxygen (NCD 240.2). A claim with a CPT code that is technically billable but paired with an ICD-10 outside the LCD covered list will deny CO-50 (non-covered, not medically necessary). Documentation must support both the diagnosis specificity and the service-level criteria the LCD requires — frequency, duration, prior-therapy attempts.
Medicare Secondary Payer (MSP) coordination
Medicare Secondary Payer rules under 42 CFR 411 require billing the primary insurer first when the beneficiary is covered by a Group Health Plan through active employment, has end-stage renal disease in the 30-month coordination window, or has workers' compensation, no-fault, or liability coverage related to the service. The MSP questionnaire must be completed and updated, and the primary EOB attached when Medicare receives the secondary claim. Skipping the MSP check at intake — common in practices that default-bill Medicare on every 65-plus patient — creates take-back demands that age into bad debt because the primary payer's timely filing window has already closed.
Crossover claims: Medicare to Medicaid (QMB beneficiaries)
Qualified Medicare Beneficiaries (QMBs) are dual-eligible patients whose state Medicaid program pays the Medicare cost-sharing (deductibles and coinsurance). Federal law prohibits balance-billing QMB patients for these amounts. Medicare automatically crosses over the claim to the state Medicaid program through the COBA (Coordination of Benefits Agreement) process, but state Medicaid reimbursement caps are often set at the Medicaid fee schedule — meaning the crossover frequently pays nothing because Medicare already paid above the Medicaid allowable. Practices that bill QMB patients for the residual coinsurance violate §1902(n)(3)(B) of the Social Security Act and risk Medicare exclusion.
What We Handle for Medicare
MAC-specific submission and LCD-aligned documentation
Claim routing to the correct A/B MAC jurisdiction with documentation packages aligned to that MAC's active LCD policies. Cross-jurisdiction practices get per-location coding rules so a single claim never gets adjudicated against the wrong MAC's coverage criteria.
ABN workflows and modifier GA/GX/GY/GZ discipline
Standardized ABN (Form CMS-R-131) issuance for medically-necessary frequency overruns, statutorily excluded services, and clinician-driven non-covered care. Modifier selection logic that protects the patient-liability path while keeping audit-defensible documentation in the record.
LCD/NCD validation pre-submission
Pre-bill scrubbing against the active NCD library and the rendering MAC's LCD policy set. ICD-10 specificity coaching to prevent CO-50 medical-necessity denials and frequency-limit checks against Medicare's MUE/NCCI edits before claims hit the door.
MSP screening and secondary-claim coordination
MSP questionnaire workflows at intake, primary EOB attachment, and 30-month ESRD coordination tracking. Working aged MSP take-backs through the MSPRC (Medicare Secondary Payer Recovery Contractor) process before they age into write-offs.
QMB and dual-eligible crossover management
QMB status verification at eligibility, COBA crossover monitoring, and balance-billing prevention on dual-eligible accounts. State Medicaid follow-up on crossover claims that fail to auto-adjudicate within the expected window.
Medicare appeals through the five-level process
Redetermination requests to the MAC, reconsideration to the Qualified Independent Contractor (QIC), ALJ hearings at the third level, Appeals Council review, and federal court appeals when the Medicare Appeals Council denial threshold justifies the escalation. Appeal packets built to the §1869 standards CMS expects.
Codes Frequently Billed to Medicare
| Code | Description |
|---|---|
| G0438 | Initial Annual Wellness Visit (Medicare-only) |
| G0439 | Subsequent Annual Wellness Visit |
| G2211 | Visit complexity add-on for longitudinal primary care (active 1/1/2024) |
| 99490 | Chronic Care Management, first 20 minutes/calendar month |
| 99439 | Chronic Care Management, each additional 20 minutes |
| 99457 | Remote Physiologic Monitoring, first 20 minutes |
| 99497 | Advance Care Planning, first 30 minutes |
| G0444 | Annual depression screening, 15 minutes |
| G0463 | Hospital outpatient clinic visit (Medicare-specific) |
| Q5101 | Injection, filgrastim biosimilar (Zarxio) — Medicare HCPCS |
Last updated: 2026-04-22
Common Questions
Common questions about medicare billing services.
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Request Review arrow_forwardHow does Medicare timely filing work?
Medicare requires claims to be filed within one calendar year (365 days) from the date of service per 42 CFR 424.44. The clock starts on the date of service, not the discharge date, and there are no automatic exceptions for billing-system errors or staffing turnover. CMS allows a small set of administrative-error exceptions if the practice can document that the failure to file was due to error or misrepresentation by Medicare itself, but in practice these are rarely granted. Claims submitted on day 366 or later receive denial code CO-29 (the time limit for filing has expired) and the patient cannot be balance-billed for the lapse.
What is the difference between an LCD and an NCD?
A National Coverage Determination (NCD) is a Medicare-wide coverage policy issued by CMS that binds every Medicare Administrative Contractor in the country. A Local Coverage Determination (LCD) is issued by a single MAC and applies only within that MAC's jurisdiction. When CMS has not issued an NCD for a service, the MACs may issue LCDs that govern coverage in their region — which is why the same CPT code can have different documentation requirements depending on where the service is rendered. Both are searchable in the Medicare Coverage Database (MCD) at cms.gov, and both must be checked at the ICD-10 level before submitting a claim.
When does a Medicare patient need to sign an ABN?
An Advance Beneficiary Notice of Noncoverage (Form CMS-R-131) is required when a clinician believes Medicare is likely to deny a Part B service as not reasonable and necessary under §1862(a)(1) of the Social Security Act. Common triggers include frequency-limit overruns (a screening colonoscopy more often than the covered interval), services outside the LCD covered ICD-10 list, and experimental or investigational procedures. The ABN must be issued before the service is rendered, must specify the service and the estimated cost, and must give the patient the choice to proceed with personal financial responsibility. Without a properly executed ABN, the practice cannot bill the patient for the denied service.
What is Medicare Secondary Payer and when does it apply?
Medicare Secondary Payer (MSP) rules under 42 CFR 411 require Medicare to be billed second when another insurer is primary. The most common scenarios are: a beneficiary covered by a Group Health Plan through current employment of themselves or a spouse (when the employer has 20+ employees for age-based Medicare or 100+ for disability-based), end-stage renal disease patients in the 30-month coordination period, workers' compensation, no-fault auto, or third-party liability coverage. Practices must complete the MSP questionnaire at intake, refresh it periodically, and attach the primary payer's EOB to the secondary Medicare claim. Skipping this step creates demand-letter take-backs from the MSPRC.
How does the Medicare appeals process work?
Medicare uses a five-level appeal process under §1869 of the Social Security Act. Level 1 is redetermination by the MAC, due within 120 days of the initial denial. Level 2 is reconsideration by a Qualified Independent Contractor (QIC), due within 180 days of the redetermination decision. Level 3 is a hearing before an Administrative Law Judge (ALJ), available when the amount in controversy meets the annually-adjusted threshold (around $190 for 2026). Level 4 is review by the Medicare Appeals Council, and Level 5 is federal district court review when the higher amount-in-controversy threshold is met. Most overturns happen at the redetermination or QIC level when documentation is supplemented appropriately.
What is a Medicare Administrative Contractor (MAC)?
A Medicare Administrative Contractor is a private insurance company that CMS contracts with to process Medicare Part A and Part B claims for a defined geographic jurisdiction. There are 12 A/B MACs nationwide — examples include Novitas Solutions, Noridian Healthcare Solutions, Palmetto GBA, WPS Government Health Administrators, and CGS Administrators. Each MAC handles claim adjudication, provider enrollment, audits, and the issuance of Local Coverage Determinations for its region. A practice with providers in multiple states often submits to multiple MACs and must comply with each MAC's specific LCD policies, which is one of the most common sources of avoidable denials in multi-state groups.
Why do QMB patients have different billing rules?
Qualified Medicare Beneficiaries are dual-eligible patients whose state Medicaid program pays the Medicare cost-sharing — deductibles, coinsurance, and copayments — on their behalf. Section 1902(n)(3)(B) of the Social Security Act prohibits providers from balance-billing QMB patients for any Medicare cost-sharing, even when state Medicaid pays nothing because the Medicare-allowed amount already exceeds the Medicaid fee schedule. Providers identify QMB status by checking the Medicare eligibility response (270/271 transactions show the QMB indicator) and by reviewing the remittance advice for the QMB notation. Billing a QMB patient for residual cost-sharing is a federal violation and can result in Medicare program exclusion.
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