Medicare is one of the most important payers for many practices, and its enrollment process is different from commercial credentialing. It runs through federal systems, uses specific forms and identifiers, and has its own rules for effective dates, reassignment and revalidation. Getting it right the first time avoids months of unpaid claims.
This guide explains the building blocks: NPI, PECOS and the CMS-855 forms. Medicare rules and forms are updated periodically, so always confirm current requirements on CMS.gov or with your Medicare Administrative Contractor (MAC) before submitting.
Key takeaways
- Every provider needs an NPI from NPPES before enrolling in Medicare.
- Enrollment is submitted online through PECOS or on paper using the appropriate CMS-855 form.
- Providers who bill through a group usually also reassign their benefits to that group.
- Enrollment must be kept current: changes must be reported and enrollment revalidated on CMS’s schedule.
Step 1: The National Provider Identifier (NPI)
The NPI is a unique 10-digit identifier issued through the National Plan and Provider Enumeration System (NPPES). There are two types:
- Type 1: individual providers, such as physicians, nurse practitioners and therapists.
- Type 2: organizations, such as group practices and clinics.
Applying for an NPI is free. Make sure the information in NPPES (name, practice address, taxonomy) is accurate, because it should match your Medicare application.
Step 2: PECOS
PECOS (Provider Enrollment, Chain, and Ownership System) is CMS’s online system for Medicare enrollment. It is generally faster and easier to track than paper applications, and it lets you view and update enrollment records later. Access is set up through CMS’s identity management system, and organizations can authorize staff or surrogates to work on their behalf.
Step 3: The CMS-855 Forms
The paper equivalents of PECOS applications are the CMS-855 forms. The most commonly used by physician practices are:
| Form | Used for |
|---|---|
| CMS-855I | Individual physicians and non-physician practitioners, including reassignment of their benefits to a group |
| CMS-855B | Clinics, group practices and certain other suppliers |
| CMS-855O | Providers who only order or refer, and do not bill Medicare |
Institutional providers such as hospitals use the CMS-855A, and suppliers of durable medical equipment use the CMS-855S. CMS has discontinued the separate CMS-855R reassignment form; reassignments are now reported through PECOS or on the CMS-855I. Forms and versions change over time, so always download the current version from CMS.
Group Enrollment and Reassignment
When a provider works for a group practice, two enrollments are typically involved: the group’s own enrollment, and the individual’s enrollment with a reassignment of benefits to the group. The reassignment allows the group to bill and be paid for the provider’s services, and both the provider and the group must be enrolled, or enrolling at the same time. A missing reassignment is a common reason a group’s claims for a new provider are rejected.
What the Application Covers
- Identifying information and NPI
- Licenses, certifications and specialty
- Practice locations and where services are provided
- Ownership and managing control (for organizations)
- Adverse legal history, sanctions and exclusions
- Where payments should be sent, usually by electronic funds transfer
Processing, Effective Dates and Follow-Up
Your MAC processes the application, may ask for more information, and issues a decision. Processing times vary by contractor and by how complete the application is. Respond to development requests quickly; unanswered requests can lead to rejection and the need to start again.
Medicare has specific rules on effective dates. Physicians, non-physician practitioners and their organizations can generally bill retrospectively for services up to 30 days before their effective date (90 days after a Presidentially declared disaster) if circumstances prevented enrolling earlier and all other requirements were met. Confirm the rules for your situation with your MAC before scheduling Medicare patients for a new provider.
After Enrollment: Keeping It Current
- Report changes on time. Changes of ownership, adverse legal actions and practice location changes must be reported within 30 days; most other changes within 90 days. Late reporting can lead to revocation or overpayments.
- Revalidate when CMS requests it. Most providers and suppliers revalidate every five years; suppliers of durable medical equipment (DMEPOS) every three years.
- Keep NPPES and PECOS aligned so your data matches across systems.
Medicare Advantage Is Different
Medicare Advantage plans are run by private insurers. Being enrolled in traditional Medicare does not make a provider in-network with a Medicare Advantage plan; each plan has its own credentialing and contracting process. See credentialing vs payer enrollment vs contracting.
Enrolling new providers with Medicare? Tell us about your providers and locations, and we will talk through the enrollment work involved.
Learn more about our provider credentialing support, or start with our provider credentialing guide.
Frequently Asked Questions
01Do I need an NPI before enrolling in Medicare?
Yes. An NPI from NPPES is required before you can enroll in Medicare.
02Should I use PECOS or paper forms?
PECOS is generally recommended because it is faster to process, easier to track and simplifies later updates. Paper CMS-855 forms remain available.
03What is a reassignment of benefits?
It is an authorization that allows a group or organization to bill Medicare and receive payment for services an individual provider delivers. It is typically needed when a provider works for a group, and it is reported through PECOS or on the CMS-855I.
04How often must Medicare enrollment be revalidated?
Most providers and suppliers revalidate every five years; DMEPOS suppliers every three years. CMS can also request off-cycle revalidation. CMS publishes due dates, but tracking your own due date remains your responsibility.
05Does Medicare enrollment cover Medicare Advantage plans?
No. Medicare Advantage plans are private plans with their own credentialing and contracting, so providers must join each plan separately.
