Summary

How does a new practice enroll in Medicare?

In a fixed order, through PECOS: the practice enrolls as an organization, each clinician enrolls as an individual, and each clinician then reassigns payments to the practice. Filing out of order is a common cause of delay. Medicare pays a clinician's claims at the practice from the effective date on its approval letter.

Start with the record everything else copies.

Every clinician has an individual National Provider Identifier. A group practice has one of its own. Both sit in NPPES, the national register that CMS keeps and publishes.A The name, address and specialty on that record travel into the Medicare application and into every commercial file after it.

We read the NPPES record for the practice and for each clinician before anything is filed. An old suite number or a former employer's address takes minutes to correct there. Found later, it comes back as a request from the Medicare contractor, and the file sits until someone answers it.

PECOS is Medicare's own system, and it does not read CAQH.

Most commercial payers pull a clinician's history from the shared credentialing profile in the CAQH Provider Data Portal (formerly ProView). Medicare does not. It enrolls through PECOS and asks its own questions about who owns the practice and where it sees patients.

A complete CAQH profile helps with the commercial plans and does nothing for Medicare. Both files get built, and both have to agree with each other and with NPPES. CAQH also has to be re-attested on a set cycle, so a profile that was current when you filed can lapse while a commercial application is still open.

The practice first, then each clinician, then the link.

Medicare's order has three parts. The practice enrolls as an organization, on the CMS-855B. Each clinician enrolls as an individual, on the CMS-855I. Then each clinician reassigns their Medicare payments to the practice, on the same CMS-855I, so a claim billed under the group pays the group. All three can be filed in PECOS.B

Filed out of order, the pieces have nothing to attach to. A reassignment needs an enrolled practice to point at. A practice enrolled with no clinicians linked to it has nobody whose visits it can bill. When a new clinician joins a practice Medicare has already enrolled, the first step drops away and the other two remain.

We price Medicare like any other payer on the list. A group pays $450 for the practice's own application and $350 for each clinician. A solo clinician who owns the practice pays one fee per payer, $450, and it covers each Medicare form that owner files.C

Timing, and the one date that matters.

Of the payers a new practice files with, Medicare usually answers first. The commercial plans take months, and Medicaid depends on the state.D

The answer that counts is the effective date on Medicare's approval letter. For a physician or a nurse practitioner, physician assistant or other non-physician practitioner, Medicare sets that date at the later of two days: the day it received an application it went on to approve, or the day the clinician first saw patients at the new location.B Medicare also allows a short window of billing before that date when circumstances kept the clinician from enrolling sooner, and a longer one after a presidentially declared disaster.B Medicare accepts an application up to 60 days before the effective date listed on it, and it can return one that arrives sooner.B We file each clinician's application once the practice details are settled and that window is open, ahead of the start date wherever we can.

When MGMA polled medical groups, 54% reported that denials tied to credentialing were rising.E A denial of that kind is one the enrollment file is kept to prevent.

What a new clinician can bill while the file is open.

Seeing patients before the effective date is allowed. Billing Medicare under the new clinician's own name for those visits is the risk. Medicare's incident-to rule can let a visit bill under an enrolled physician instead, on two strict conditions: that physician supervises directly, on site, and the visit follows a plan of care the physician already set.F

It is a bridge for supervised work. It does not stand in for enrollment, and commercial plans set their own limits on it. The answer for each plan goes into the enrollment file before anyone bills under it.

Two Medicare enrollments that sit outside the main file.

The first is equipment. A practice that supplies durable medical equipment needs its own Medicare enrollment as a DMEPOS supplier. The plainest case is a dentist fitting an oral appliance for sleep apnea. It is billed to medical insurance under HCPCS E0486, and for Medicare the dentist has to be enrolled as the supplier.G

The second is Medicare Advantage. Those plans are run by private insurers with networks of their own, held to CMS network adequacy standards.H Enrollment in traditional Medicare does not put a clinician in any of them. Each Medicare Advantage plan your patients carry is its own application, and its panel can be closed. Our note on closed panels covers what happens then.

To open a Medicare file we need each clinician's NPI, the practice's tax ID and service address, and the names of its owners. We gather the rest. Once the effective date is set, Medicare claims go out under it, and if we run your billing we follow each one to a payment or written payer decision.

Sources

  1. CMS, the National Plan and Provider Enumeration System (NPPES) records and published NPI files. Read 2026.
  2. Primary sources: 42 CFR part 424, subpart P (sections 424.520, 424.521 and 424.526, effective dates, retrospective billing and returned applications), the CMS-855 enrollment applications, and the CMS Medicare Program Integrity Manual, chapter 10. Read 2026.
  3. HRI Med published fees. Current as of 2026.
  4. GetPracticeHelp, payer-by-payer credentialing timeline guide. A vendor guide, not a measured survey. Read 2026.
  5. MGMA Stat poll, N=425, asking members whether credentialing-related denials were rising. Poll taken 2021.
  6. Medical Economics, on the requirements for incident-to billing. Read 2026.
  7. Nierman Practice Management, on billing oral appliances to medical insurance, and CMS Local Coverage Determination L33611. Read 2026.
  8. drcredentialing.us, guide to closed insurance panels and network adequacy. Read 2026.