A Medicare Administrative Contractor, or MAC, is a private insurance company that the Centers for Medicare & Medicaid Services (CMS) pays to run the day-to-day operations of Original Medicare in a specific region of the country. Twelve A/B MACs handle Part A and Part B claims, and four DME MACs handle durable medical equipment claims.1Centers for Medicare & Medicaid Services. Medicare Administrative Contractors (MACs) Who are the MACs Together they process billions of dollars in claims each year, enroll the providers who treat Medicare patients, decide certain local coverage questions, and handle the first level of appeals when a claim is denied.
If you have Original Medicare, your MAC is the entity that actually pays your doctor and generates the notice you get in the mail. If you are a provider billing Medicare, your MAC is your point of contact with the program.
What a MAC Actually Does
The core job is processing Medicare Fee-for-Service claims. A hospital, physician, or supplier submits a bill for treating a Medicare patient, and the MAC reviews the claim against Medicare rules and issues payment. Most claims come in electronically through Electronic Data Interchange (EDI), and the MAC handles enrollment, credentials, and format testing for providers using that system.2Centers for Medicare & Medicaid Services. Electronic Data Interchange (EDI) Support Providers must file within one calendar year of the date of service, and missing that deadline generally means the claim will not be paid.3eCFR. 42 CFR 424.44 – Time Limits for Filing Claims
Beyond claim payment, MACs do four other things worth knowing about:
- Provider enrollment. Before any provider can bill Medicare, they must enroll through their MAC, and they must revalidate periodically to keep billing privileges active. MACs send revalidation notices roughly two to three months before the deadline and no longer grant extensions for late responses.4Centers for Medicare & Medicaid Services. Revalidations (Renewing Your Enrollment)5Centers for Medicare & Medicaid Services. Provider Enrollment Revalidation Cycle 2 FAQs
- Cost reports. For institutional providers like hospitals and skilled nursing facilities, the MAC accepts, audits, and settles the annual Medicare cost report that documents what a facility spent delivering care to Medicare patients.6U.S. Department of Health and Human Services Office of Inspector General. Medicare Administrative Contractor Cost Report Oversight – Contract Review
- Local coverage decisions. Where Medicare’s national rules are silent, the MAC decides whether a service is reasonable and necessary through a Local Coverage Determination.
- Beneficiary communication. The Medicare Summary Notice showing what Medicare paid and what you might owe is generated by your MAC, and it explains any denial and your appeal rights.7Centers for Medicare & Medicaid Services. Medicare Summary Notice
MACs also provide educational materials, workshops, and webinars for providers on billing, coding, and compliance, and they are the first line of support for EDI questions.
How the Jurisdictions Are Set Up
Each MAC covers a defined geographic jurisdiction, and you do not choose which one you use. Providers work with the MAC assigned to where they practice, and beneficiaries interact with the MAC assigned to where they received care. The 12 A/B MACs process both Part A (hospital and facility) and Part B (physician and outpatient) claims, and four of them also handle Home Health and Hospice claims. The 4 DME MACs operate on their own regional map for durable medical equipment, orthotics, and prosthetics.1Centers for Medicare & Medicaid Services. Medicare Administrative Contractors (MACs) Who are the MACs
The companies currently holding MAC contracts include Noridian Healthcare Solutions, Novitas Solutions, Palmetto GBA, National Government Services, First Coast Service Options, Wisconsin Physicians Service (WPS), and CGS Administrators.8Centers for Medicare & Medicaid Services. Review Contractor Directory – Interactive Map CMS awards these contracts through competitive bidding under 42 U.S.C. ยง 1395kk-1, and each contract can run up to ten years before competition must be reopened.9Office of the Law Revision Counsel. 42 US Code 1395kk-1 – Contracts with Medicare Administrative Contractors
Why the Same Service Can Be Covered Differently State to State
One consequence of the MAC structure surprises people the first time they run into it: a service covered by Medicare in one part of the country may be denied in another. That happens because MACs issue their own Local Coverage Determinations, or LCDs. An LCD is a MAC’s decision about whether a service is reasonable and necessary under Medicare, applied across that MAC’s entire jurisdiction.10Centers for Medicare & Medicaid Services. Local Coverage Determinations National Coverage Determinations from CMS override LCDs when they exist, but many services have no national determination, which leaves the local MAC policy in charge.
The LCD process is open to public participation. Anyone can submit a written request for a new LCD backed by peer-reviewed evidence. The MAC reviews the request within 60 days, and if it moves forward, publishes a proposed LCD, opens at least a 45-day public comment period, and holds an open meeting where interested parties can present evidence. The final LCD takes effect no sooner than 45 days after publication, and the MAC generally has 365 days from the proposed version to finalize or retire it.11Centers for Medicare & Medicaid Services. Local Coverage Determination Process and Timeline Providers billing across multiple jurisdictions have to track the LCDs in each one.
The First Level of Appeal Runs Through the MAC
When a claim is denied or paid at a lower amount than expected, the MAC handles the first appeal, called a redetermination. A redetermination is a fresh review of the claim by MAC staff who were not involved in the original decision.12Centers for Medicare & Medicaid Services. First Level of Appeal – Redetermination by a Medicare Contractor You have 120 days from receiving the initial determination to file, and the notice is presumed received five calendar days after it was dated. The request must be in writing and include the beneficiary’s name and Medicare number, the specific services and dates in question, and an explanation of why the decision was wrong. The MAC generally issues its decision within 60 days, and filing costs nothing.
If the redetermination goes against you, the appeal moves to a Qualified Independent Contractor, which is a separate entity from the MAC, and from there potentially to an Administrative Law Judge, the Medicare Appeals Council, and federal court.13Centers for Medicare & Medicaid Services. Medicare Parts A and B Appeals Process A MAC denial is not the last word.
How to Find Your MAC
CMS keeps an interactive map that shows which A/B MAC and DME MAC covers each state, along with contact information for the contractor. The Review Contractor Directory is the fastest way to identify your MAC and reach it directly with a question about a claim, an enrollment, or a coverage policy.8Centers for Medicare & Medicaid Services. Review Contractor Directory – Interactive Map Knowing which MAC handles your claims matters because the policies, educational resources, and coverage rules can differ by jurisdiction, and every question about a Medicare payment eventually points back to the MAC that processed it.