> ## Documentation Index
> Fetch the complete documentation index at: https://mso.getlemma.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Medicare (fee-for-service)

> Medicare FFS profile: MACs, PECOS enrollment, the 12-month filing limit, LCDs, and the five-level appeals process.

**Medicare fee-for-service** — Parts A and B — is the federal program administered regionally through **Medicare Administrative Contractors (MACs)**. It is the reference frame for the entire US payment system: most commercial fee schedules are expressed as a percentage of the Medicare Physician Fee Schedule.

**Payer content ages fastest of anything on this site.** Portals move, forms change, payer IDs get reassigned, and **timely filing limits are contract-specific regardless of what any table says**. Treat this page as orientation; the payer's own current documentation and **your executed contract** are authoritative. **Checked August 2026.**

## Structure

| Part       | Covers                                           | Administered by |
| ---------- | ------------------------------------------------ | --------------- |
| **Part A** | Hospital insurance                               | MACs            |
| **Part B** | Physician and outpatient services                | MACs            |
| Part C     | Medicare Advantage — private plans replacing A/B | MA plans        |
| Part D     | Prescription drugs                               | Part D sponsors |

**Find your MAC** through [CMS](https://www.cms.gov/medicare/coding-billing/electronic-billing/find-your-mac-page). Your MAC issues **local coverage determinations (LCDs)** that affect medical necessity in your region — two practices in different MAC jurisdictions can get different answers on the same service.

## Enrollment

Through **[PECOS](https://pecos.cms.hhs.gov/)**:

| Form         | Purpose                                                                                   |
| ------------ | ----------------------------------------------------------------------------------------- |
| **CMS-855B** | Enroll the group                                                                          |
| **CMS-855I** | Enroll each individual clinician                                                          |
| **CMS-855R** | **Reassign benefits** to the group — without it, the group cannot bill for that clinician |
| **CMS-588**  | EFT authorization                                                                         |
| **CMS-460**  | Participating provider agreement                                                          |

Expect **60–120 days**. Ownership and managing control disclosure on the 855B requires care in an MSO-PC structure — see [Enroll in Medicare](/guides/enrollment/enroll-in-medicare).

On approval you receive a **PTAN**, a MAC-assigned identifier distinct from the NPI. Record group and individual PTANs.

## Timely filing

**12 months from the date of service** — set by statute and regulation.<sup>[1](#sources)</sup> One of the few limits that is genuinely fixed rather than contractual.

## Appeals — the five levels

| Level              | Decided by                         |
| ------------------ | ---------------------------------- |
| 1. Redetermination | The MAC                            |
| 2. Reconsideration | A Qualified Independent Contractor |
| 3. Hearing         | An Administrative Law Judge (OMHA) |
| 4. Review          | The Medicare Appeals Council       |
| 5. Judicial review | Federal district court             |

Each level has its own deadline; levels 3 and 5 have amount-in-controversy thresholds. Most provider appeals resolve at level 1 or 2.

## Revalidation

**Every five years for most providers** (three for DMEPOS). **Notices go to the correspondence address in PECOS** — if nobody monitors it, the first you'll hear is when billing privileges are deactivated and claims stop.

Check your date directly in the [Medicare Revalidation Lookup Tool](https://data.cms.gov/tools/medicare-revalidation-list).

## Quirks worth knowing

* **Sequestration** appears as CO-253, a statutory payment reduction. Write it off.
* **Opt-out physicians** cannot reassign benefits to your group — check status during clinician vetting
* **Incident-to and split/shared** rules are Medicare-specific and frequently misapplied
* **Crossover** to secondary payers is automatic for many claims — submitting the secondary separately produces duplicate denials
* **The 60-day overpayment rule** applies to Medicare. See [Report and return overpayments](/guides/compliance/report-and-return-overpayments).

## Sources

1. Social Security Act § 1842(b)(3)(B); 42 C.F.R. § 424.44. CMS, [Medicare Claims Processing Manual](https://www.cms.gov/regulations-and-guidance/guidance/manuals/internet-only-manuals-ioms-items/cms018912).


## Related topics

- [The US payer landscape](/concepts/payments/the-payer-landscape.md)
- [Payers vs insurance companies (they're not synonyms)](/concepts/payments/payers-vs-insurance-companies.md)
- [Enroll and contract with commercial payers](/guides/enrollment/enroll-with-commercial-payers.md)
- [Set up EDI, ERA, and EFT with each payer](/guides/enrollment/set-up-edi-era-eft.md)
- [File appeals](/guides/billing/file-appeals.md)
- [How to use the payer reference](/reference/payers/overview.md)
- [Payer enrollment & submission links](/reference/payers/enrollment-links.md)
- [Timely filing limits by payer](/reference/payers/timely-filing-limits.md)