What Is Medicare Billing?
Medicare billing submits claims to the A/B Medicare Administrative Contractor (MAC) for the jurisdiction where the service was rendered: Part A institutional claims on the UB-04, Part B professional claims on the CMS-1500. CMS contracts 12 A/B MAC jurisdictions and 4 DME MAC jurisdictions, held by fewer companies than there are jurisdictions. Compliance turns on national NCD policy, the issuing MAC's LCD policy, an ABN before a service Medicare is expected to deny, and a filing deadline of one calendar year from the date of service under 42 CFR 424.44.
- MAC jurisdiction: the claim goes to the A/B MAC for the jurisdiction where the service was rendered
- Part A: institutional billing on UB-04. Part B: professional billing on CMS-1500
- LCD and NCD compliance, plus an ABN (Form CMS-R-131) before a service Medicare is expected to deny
- Timely filing: one calendar year from the date of service under 42 CFR 424.44, with narrow exceptions
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Medicare billing runs through regional contractors, and the contractor map is the first thing a practice has to get right. CMS contracts 12 A/B Medicare Administrative Contractor (MAC) jurisdictions plus 4 DME MAC jurisdictions, and the 12 A/B jurisdictions are held by seven companies — Novitas Solutions, Noridian Healthcare Solutions, Palmetto GBA, National Government Services, Wisconsin Physicians Service, CGS Administrators and First Coast Service Options — most of which hold two jurisdictions each. The contractor and the jurisdiction are therefore not the same thing: two jurisdictions run by the same company still carry separate Local Coverage Determinations. Part A institutional claims travel on the UB-04 and Part B professional claims on the CMS-1500, and the claim must be filed no later than one calendar year after the date of service under 42 CFR 424.44(a). In fiscal year 2024 the MACs processed more than 1.1 billion Medicare fee-for-service claims — about 193 million Part A and 927 million Part B — for roughly 33.9 million fee-for-service beneficiaries, and paid about $459.7 billion in benefits (CMS, What's a MAC, read 17 September 2026). This page covers how Medicare billing plays out across MAC routing, ABN documentation under section 1879 of the Social Security Act, LCD and NCD compliance, Medicare Secondary Payer coordination, QMB crossover claims to state Medicaid programs, and the five levels of appeal.
Medicare at a Glance
Medicare fee-for-service beneficiaries
~33.9 million
Source: CMS, What's a MAC (FY2024), verified 2026-09-17
A/B MAC jurisdictions
12, held by 7 companies
Source: CMS, Who are the MACs / MACs by State, verified 2026-09-17
Medicare timely filing
1 calendar year from DOS
Source: 42 CFR 424.44(a)(1), verified 2026-09-17
FFS claims processed (FY2024)
~1.1 billion
Source: CMS, What's a MAC, verified 2026-09-17
FFS benefits paid (FY2024)
~$459.7 billion
Source: CMS, What's a MAC, verified 2026-09-17
ALJ amount in controversy (CY2026)
$200
Source: CMS, third level of appeal, verified 2026-09-17
Billing Challenges Specific to Medicare
MAC jurisdiction routing — different rules by region
Medicare claims route to one of 12 A/B MAC jurisdictions by where the service was rendered, and each MAC publishes its own Local Coverage Determinations (LCDs) on top of national CMS policy. Novitas Solutions covers a different policy footprint than Noridian or Palmetto GBA, so a group with providers in two jurisdictions is applying two documentation standards to the same procedure. The jurisdiction matters more than the company name: seven companies hold the 12 A/B jurisdictions and most hold two, and two jurisdictions run by one contractor still carry separate LCD sets. The pre-bill check is which policy is active in that jurisdiction, for that code, on that date of service.
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 set out covered diagnosis lists and documentation requirements, and the numbering is unforgiving: sleep testing for obstructive sleep apnea is NCD 240.4.1, while NCD 240.4 immediately beside it is CPAP therapy — cite the wrong one in an appeal and the argument answers a policy the denial was not issued under. A CPT code that is billable in principle but paired with a diagnosis outside the covered list denies as not medically necessary under CARC 50. 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 recovery demands that age into bad debt because the primary payer's filing window has already closed. Those demands come from the Commercial Repayment Center where a Group Health Plan should have paid first, and from the Benefits Coordination and Recovery Center on liability, no-fault and workers' compensation cases. The Medicare Secondary Payer Recovery Contractor that older billing guidance still names is not the entity you deal with.
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 recovery demands through the Commercial Repayment Center (Group Health Plan cases) and the Benefits Coordination and Recovery Center (liability, no-fault and workers' compensation) 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 to an office/outpatient E/M for continuing, longitudinal care |
| 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, 5 to 15 minutes |
| G0463 | Hospital outpatient clinic visit (Medicare-specific) |
| Q5101 | Injection, filgrastim-sndz, biosimilar (Zarxio), 1 microgram — HCPCS Level II |
Last updated: 2026-10-02
Common Questions
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Request ReviewHow does Medicare timely filing work?
Medicare requires the claim to be filed no later than one calendar year after the date of service under 42 CFR 424.44(a)(1). The clock starts on the date of service, not the discharge date, and nothing in the rule excuses a billing-system outage or staffing turnover. The exceptions in 424.44(b) are four and they are specific: error or misrepresentation by a Medicare contractor or an HHS agent acting within its authority; retroactive Medicare entitlement; retroactive entitlement where a state Medicaid agency then recovered its payment six months or more after the service; and retroactive disenrollment from a Medicare Advantage or PACE organization that then recovered its payment. Each extends filing only through the last day of the sixth calendar month after the triggering notice, and the paragraph (b)(1) exception is unavailable more than four years after the date of service. If the deadline itself falls on a federal nonworkday, it moves to the next workday. Outside those exceptions a late claim denies under CARC 29 for untimely filing. Regulation text read at 42 CFR 424.44 on 17 September 2026.
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 issued to an Original Medicare fee-for-service beneficiary where payment is expected to be denied — typically a Part B service the clinician believes Medicare will find not reasonable and necessary under section 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 is issued before the service is furnished, and its purpose is narrow: it transfers potential financial liability for that item or service to the beneficiary. CMS publishes the form, the form instructions and the issuing guidelines (Medicare Claims Processing Manual, Pub. 100-04, Chapter 30, from Section 50), and those are what the workflow should be built from. 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 date the initial claim determination is received. Level 2 is reconsideration by a Qualified Independent Contractor (QIC), due within 180 days of receiving the redetermination decision — and CMS presumes that decision was received five days after the date on the notice unless there is evidence otherwise, which is five days practices routinely lose. Level 3 is a hearing before an Administrative Law Judge (ALJ), available only when the amount remaining in controversy meets the threshold CMS republishes each year — $200 for calendar year 2026. Level 4 is review by the Medicare Appeals Council, and Level 5 is federal district court review, which carries a much higher amount-in-controversy threshold set in the same annual Federal Register notice. Most overturns happen at the redetermination or QIC level when documentation is supplemented appropriately. Filing deadlines and the CY2026 threshold read from the CMS appeal pages on 17 September 2026.
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 MAC jurisdictions and 4 DME MAC jurisdictions, and seven companies hold the 12: Wisconsin Physicians Service (J5, J8), National Government Services (J6, JK; operating as Wellpoint Federal since April 2026), CGS Administrators (J15), Noridian Healthcare Solutions (JE, JF), Novitas Solutions (JH, JL), Palmetto GBA (JJ, JM) and First Coast Service Options (JN). Four of those A/B MACs also process home health and hospice claims for areas that do not match their A/B footprint. Each MAC handles claim adjudication, provider enrollment, audits and its own Local Coverage Determinations, so a practice in two jurisdictions complies with two LCD sets even when one company holds both — one of the most common sources of avoidable denials in multi-state groups. Jurisdiction assignments read from the CMS MACs-by-State list on 17 September 2026.
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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