Medicare Claims and Billing: How the Process Works

Medicare claims and billing form the operational backbone of the program, determining how providers receive payment and how beneficiaries are charged for covered services. The process spans multiple parties — including providers, Medicare Administrative Contractors, and CMS itself — and follows a structured sequence governed by federal statute and regulation. Understanding how claims move through this system helps beneficiaries interpret their Medicare Summary Notices, identify potential errors, and exercise their rights under the Medicare appeals process.

Definition and scope

A Medicare claim is a formal request for payment submitted to Medicare after a covered service has been rendered. Claims can be filed by providers (assigned claims) or, less commonly, by beneficiaries themselves (unassigned claims). The Centers for Medicare & Medicaid Services (CMS), the federal agency administering Medicare, contracts with private entities called Medicare Administrative Contractors (MACs) to process the vast majority of claims on its behalf (CMS Medicare Administrative Contractors).

The billing system distinguishes between two primary claim types:

• Institutional claims — submitted on a UB-04 form (CMS-1450) by hospitals, skilled nursing facilities, home health agencies, and hospices
• Professional claims — submitted on a CMS-1500 form by physicians, non-physician practitioners, and outpatient suppliers

These form types correspond to the coverage divisions within Medicare itself. Institutional claims typically relate to Part A hospital insurance, while professional claims generally fall under Part B medical insurance.

How it works

The claims and billing process follows a defined sequence from service delivery to payment determination:

1. Service rendered — A beneficiary receives a covered service from a participating or non-participating provider.
2. Claim submission — The provider submits a claim electronically to the appropriate MAC. CMS requires electronic submission for most providers under the Administrative Simplification provisions of HIPAA (45 CFR Part 162).
3. MAC processing — The MAC reviews the claim for completeness, medical necessity, and coverage eligibility. This includes automated edits and, in some cases, manual review.
4. Payment determination — If approved, the MAC pays the provider according to the Medicare fee schedule or prospective payment system applicable to that service category. For Part B services, Medicare generally pays 80 percent of the approved amount after the annual deductible is met (CMS Medicare Costs).
5. Remittance advice — The provider receives an Electronic Remittance Advice (ERA) explaining the payment, adjustments, or denial reasons.
6. Medicare Summary Notice — Beneficiaries enrolled in Original Medicare receive a Medicare Summary Notice (MSN) quarterly, detailing services billed, amounts approved, and any beneficiary liability.

Timely filing limits apply: providers must submit claims within 1 calendar year of the date of service, as established under the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (CMS Timely Filing).

Common scenarios

Assigned vs. non-assigned billing: When a provider accepts assignment, they agree to accept Medicare's approved amount as payment in full and bill the beneficiary only for applicable cost-sharing. Non-participating providers who do not accept assignment may charge up to 15 percent above the Medicare-approved amount — a ceiling known as the limiting charge (Medicare Rights Center). Beneficiaries with Medigap supplement insurance may have some or all of this cost-sharing covered depending on their plan type.

Coordination of benefits: When Medicare acts as a secondary payer — for example, when an employer group health plan is primary — the billing sequence changes materially. The primary payer adjudicates the claim first, and Medicare pays only after reviewing the primary payer's explanation of benefits. Full detail on these rules appears under Medicare as secondary payer.

Claim denials: Claims are denied for reasons including lack of medical necessity, missing documentation, duplicate billing, or services excluded from coverage. A denied claim does not foreclose payment — beneficiaries and providers retain the right to request redetermination through the five-level Medicare appeals structure.

Billing errors and fraud: Upcoding (billing for a higher-cost service than delivered), unbundling (separating charges that should be billed together), and billing for services not rendered are among the billing irregularities tracked by CMS's program integrity contractors. These practices carry civil monetary penalties and potential exclusion from federal healthcare programs under 42 U.S.C. § 1320a-7a (CMS Program Integrity). Detailed guidance on recognizing and reporting these patterns is covered under Medicare fraud and abuse.

Decision boundaries

Several threshold questions determine how a claim is processed and who bears financial responsibility:

Covered vs. non-covered services: Medicare pays only for services that are medically necessary and explicitly covered under statute or CMS national or local coverage determinations. Services listed in what Medicare does not cover generate no payment obligation from the program regardless of provider billing.

Medicare Advantage vs. Original Medicare billing: Beneficiaries enrolled in Medicare Advantage do not have claims processed by MACs. Instead, the private plan administers claims under its own network and prior authorization rules, subject to CMS oversight. Providers must bill the plan directly, not CMS. This is a structurally distinct pathway from Original Medicare.

Advance Beneficiary Notice (ABN): When a provider believes Medicare may deny a service as not medically necessary, the provider must issue a signed ABN before delivering the service. Without a valid ABN, a non-participating provider cannot bill the beneficiary if Medicare denies the claim. With a signed ABN, the beneficiary accepts financial liability for that specific service.

Beneficiaries seeking a full orientation to how these billing decisions fit within the broader program can start at the Medicare home resource hub, which links to eligibility, cost, and coverage topics including Medicare costs, premiums, deductibles, and copays.