What Medicare enrollment actually is
Medicare enrollment is how providers and groups become eligible to bill Medicare Part B (professional services) or Part A (institutional). It's separate from commercial credentialing — Medicare doesn't use CAQH. Every enrollment goes through the PECOS portal or paper 855 forms.
The 855 forms you'll actually use
- CMS-855I — Individual provider enrollment (physician, NP, PA, therapist, etc.).
- CMS-855R — Reassignment of benefits: the individual reassigns payment to a group TIN.
- CMS-855B — Group or clinic enrollment (the entity itself).
- CMS-855S — DMEPOS suppliers.
- CMS-588 — EFT authorization so Medicare can direct-deposit payments.
A new group starts with the 855B; each provider files an 855I plus an 855R to reassign to the group.
Effective date & retro-billing
Medicare's effective date is generally the later of (a) the date PECOS received a complete application, or (b) the date the provider began furnishing services at the location. Providers can retro-bill up to 30 days before the effective date (60 days in a Presidentially-declared disaster area). Missing the 30-day window means unbillable services — file early.
Common Medicare enrollment mistakes
- Filing 855I without the matching 855R — payment has nowhere to go.
- Group NPI or TIN mismatch between PECOS and IRS records.
- Practice location addresses that don't match the state license.
- Missing CMS-588 EFT form — enrollment approves but no payment flows.
- Not revalidating every 5 years — CMS deactivates providers who miss it.
Timelines
Clean Medicare applications typically approve in 45–90 days. Contractor backlogs vary by state (Novitas, Palmetto, NGS, WPS, First Coast, Noridian). For a full payer breakdown see the payer timeline guide.
How Credify handles Medicare
Credify Health files every 855 form on your behalf, manages PECOS, tracks the MAC contractor, and captures every allowable retro-effective date. Related: Medicaid enrollment by state.