Overview
A Medicare Administrative Contractor (MAC) is a private-sector organization that CMS contracts with to perform the operational functions of Medicare fee-for-service (FFS) claims administration for a defined geographic jurisdiction. MACs are the primary Medicare operational interface for providers — processing claims, handling enrollment, conducting medical review, publishing Local Coverage Determinations (LCDs), adjudicating appeals, and providing provider education and outreach.
There are two MAC structures. A/B MACs (sometimes called Medicare Administrative Contractors for Part A and Part B) handle Part A institutional claims (hospital inpatient, home health, hospice) and Part B professional and outpatient claims within their geographic jurisdiction. 12 A/B MACs cover the United States, each serving specific states. DME MACs handle Durable Medical Equipment, Prosthetics, Orthotics, and Supplies (DMEPOS) claims. 4 DME MACs cover the United States, each serving a specific region regardless of patient location.
Major MACs as of 2025 include: Noridian Healthcare Solutions (Jurisdictions F, J, A/B), Palmetto GBA (multiple jurisdictions including Jurisdiction M), CGS Administrators (Jurisdictions 15 A/B, DME Jurisdiction C), WPS (Jurisdiction 5 A/B), Novitas Solutions (multiple jurisdictions), First Coast Service Options (Jurisdiction N), National Government Services (Jurisdictions 6 A/B and K). Contract assignments change periodically through CMS competitive procurement cycles.
For RCM, the operational MAC relationship touches every Medicare FFS claim. Providers enroll in Medicare through their MAC (PECOS and paper enrollment); submit claims through their MAC (clearinghouse and EDI submissions); receive payments from their MAC; receive denials and ADRs from their MAC; submit redeterminations to their MAC; receive Medicare Secondary Payer processing through their MAC; receive education and provider outreach from their MAC.
MAC jurisdictions matter for specific operational activities. LCDs are jurisdiction-specific — the LCD applying to a service depends on the MAC where the claim is processed. Provider education webinars, newsletters, and specific policy interpretations may differ across MACs. RCM teams for multi-state providers must maintain awareness of multiple MAC rules and LCDs.
Provider enrollment is managed through the MAC via PECOS. Changes in provider location, employment, services offered, or practice structure require MAC notification. Revalidation cycles (every 3–5 years depending on provider type) are managed through the MAC. Enrollment errors or delays have cascading payment consequences.
Medical review and program integrity functions include: Targeted Probe and Educate (TPE) programs — specific provider reviews; Complex or routine post-payment review; Prior-authorization programs for specific services; Pre-payment review for providers with elevated error rates; Fraud investigation referrals to Unified Program Integrity Contractors (UPICs) or HHS-OIG.
MAC technology infrastructure varies. Most operate through CMS-approved claim processing systems with MAC-specific front-end systems for provider enrollment (PECOS), claim submission (Medicare clearinghouses), correspondence (provider portals), and appeals (MAC-specific portals). Provider RCM teams typically have MAC-specific logins and processes.
MAC performance is measured by CMS on multiple dimensions: claim processing accuracy, payment timeliness, customer service quality, medical review accuracy, and operational compliance. CMS publishes MAC performance data; MACs compete for contract renewals based on performance.
Industry benchmark
CMS Medicare Administrative Contractor program documentation. Medicare Program Integrity Manual. MAC jurisdictional maps (CMS website).
Worked example
A multi-state hospital system has facilities in Texas (Novitas A/B MAC jurisdiction H), New Mexico (Noridian A/B Jurisdiction F), and Colorado (Noridian Jurisdiction H). Provider enrollment for each facility is through the applicable MAC. Texas facility claims go to Novitas with Novitas-specific LCDs applying; New Mexico and Colorado facilities go to Noridian with Noridian LCDs. Redetermination appeals go to the respective MAC that issued the denial. Compliance and billing teams must maintain awareness of both MACs' rules, LCDs, and operational policies.
Frequently asked questions — Medicare Administrative Contractor (MAC)
How are MAC jurisdictions determined?
CMS assigns each U.S. state/territory to a specific A/B MAC jurisdiction. Provider enrollment, claims, and most operational activities flow through the MAC for the provider's location. DME claims go to DME MACs based on patient location, regardless of provider location.
What do MACs do?
Process Medicare claims, handle provider enrollment (PECOS), adjudicate redeterminations, publish LCDs, conduct medical review and ADR activities, provide provider education and outreach, handle beneficiary inquiries, and coordinate Medicare Secondary Payer processing.
How do I know which MAC serves my practice?
CMS publishes jurisdictional maps on the CMS website. MAC contract assignments occasionally change through CMS procurement cycles; provider MAC assignments update automatically for existing providers. Check CMS Medicare Administrative Contractor page for current assignments.
Can MACs publish coverage policies that differ from Medicare?
LCDs can add local detail and fill gaps where no NCD exists, but cannot conflict with national policy or statute. MACs cannot unilaterally create coverage rules beyond CMS authority. Stakeholder comment processes, CMS oversight, and legal challenge mechanisms provide checks on MAC policy authority.
Disclaimer
This glossary entry is operational reference for revenue-cycle and medical-billing professionals. It is not legal, clinical, or contractual advice. Industry benchmarks cite named public sources where available; always verify against the current guidance from the authority body before relying on a number in a contract, policy, or compliance filing.