CMS-855A vs 855B vs 855I vs 855S: Which Medicare Form Is Yours?

There are five active CMS-855 enrollment applications, and the one you need is decided by what kind of entity you are, not what kind of medicine you practice. Institutional providers file the 855A. Clinics, groups and organizational suppliers file the 855B. Individual practitioners file the 855I. Order-and-certify-only clinicians file the 855O. DMEPOS suppliers file the 855S. The 855R no longer exists.

Picking the wrong one does not usually get you a rejection letter on day two. It gets you sixty days of silence followed by a request to start over on a different form — which, if you have already opened your doors, is sixty days of unbillable care. This guide is the decision, made once, correctly.

The five forms at a glance

All of them can be filed on paper or through PECOS, the internet-based Provider Enrollment, Chain and Ownership System. PECOS is faster and gives you a status trail; the paper forms exist for edge cases and for people who want to see the whole application at once. The content is identical either way.

The CMS-855R is gone — reassignments now live on the 855I

This is the single most common piece of stale advice still circulating, so it goes first.

The CMS-855R (Reassignment of Medicare Benefits) has been discontinued. The current CMS-855I states it plainly: “All reassignment actions should now be reported via the CMS-855I.” If you are a practitioner reassigning your Medicare benefits to a group so the group can bill for your services — or terminating that reassignment, or changing it — you are filing an 855I, not a separate 855R.

One rule survives the change, and it is the one that trips up new groups: both parties must already be enrolled, or be enrolling at the same time. A practitioner cannot reassign benefits to a group that has no Medicare enrollment of its own. The concurrent path is an 855B for the group and an 855I for the practitioner, filed together. Groups that hire before they enroll discover this in week eleven.

CMS-855A — institutional providers

The 855A is for organizations that will bill Medicare Part A. The form names the eligible types directly:

• Community Mental Health Center
• Comprehensive Outpatient Rehabilitation Facility
• Critical Access Hospital
• End-Stage Renal Disease Facility
• Federally Qualified Health Center
• Histocompatibility Laboratory
• Home Health Agency
• Hospice
• Hospital
• Indian Health Services Facility
• Opioid Treatment Program (may file the 855A or the 855B)
• Organ Procurement Organization
• Outpatient Physical Therapy / Occupational Therapy / Speech Pathology Services
• Religious Non-Medical Health Care Institution
• Rural Emergency Hospital
• Rural Health Clinic
• Skilled Nursing Facility

If your organization type is not on that list, your MAC — not a consultant, not a forum — is the authority on which form applies. Call before you file.

An 855A applicant needs a Type 2 (organizational) NPI, and per Section 125 of the Consolidated Appropriations Act of 2021, an action plan must accompany the enrollment application.

The 855A is not a form, it is a five-step certification

The reason 855A timelines run long is that the application is one step of five. CMS describes the process this way:

1. You submit the CMS-855A and supporting documentation to your MAC.
2. The MAC reviews it and makes a recommendation for approval or denial to the State survey agency, copying CMS.
3. The State agency or an approved accreditation organization conducts a survey and makes a certification recommendation to CMS.
4. The MAC conducts a second review to verify you still meet enrollment requirements before billing privileges are granted.
5. CMS makes the final decision. If approved, you typically sign a provider agreement.

Two consequences follow. First, a clean application does not shorten the survey queue — those are different agencies with different backlogs. Second, if the MAC asks for additional documentation at any point, you have 30 days to supply it under 42 CFR 424.525(a)(1). Missing that window restarts far more than the request.

Our Medicare & Medicaid enrollment work sits at steps 1, 2 and 4. Steps 3 and 5 belong to the survey agency and CMS, and anyone who tells you they can accelerate them is selling something that does not exist.

CMS-855B — clinics, group practices and other suppliers

The 855B enrolls organizations that bill Part B. In the form’s own framing, that means “a medical practice, group/clinic or other supplier that will bill for Medicare Part B services (e.g., group practices, clinics, independent laboratories, portable x-ray suppliers).” Ambulatory surgery centers and portable x-ray suppliers appear as certified Part B providers that use the 855B to report a change of ownership. Opioid treatment programs may use either the 855A or the 855B.

The 855B is also the form you use when a group accepts a reassignment of benefits from a practitioner, terminates one, or changes the reassignment information — the group’s half of the transaction whose individual half now lives on the 855I.

Like the 855A, it requires a Type 2 NPI, and the legal business name and TIN on the application must match the ones used to obtain that NPI. A mismatch there is one of the quiet, high-frequency causes of a returned application, because nothing about the error is visible to the person filling out the form.

There is one distinction worth internalising: a hospital department that bills Part B practitioner services files an 855B even though the hospital itself is an 855A provider. Same building, two applications, two enrollment records.

CMS-855I — individual physicians and non-physician practitioners

The 855I enrolls the individual clinician. Physicians and eligible professionals as defined in section 1848(k)(3)(B) of the Social Security Act use it to obtain billing privileges, revalidate, reactivate, move to a new MAC jurisdiction, report changes — and, since the 855R was retired, to handle every reassignment action.

Two situations that look like they need a group form but do not:

• The sole-owner professional entity. An individual practitioner who has formed a professional corporation, professional association or LLC of which they are the sole owner files an 855I, not an 855B.
• Moving from order-and-certify to billing. A clinician currently enrolled on an 855O who now wants to submit claims files an 855I.

Physician assistants have their own reassignment history worth flagging: PAs are named explicitly in the 855I’s reassignment instructions, which is a change from the era when a PA’s Medicare relationship ran only through an employer. If you are enrolling PAs, see physician assistant credentialing for the state-level supervision documents that ride alongside.

There is no application fee on the 855I. If a service quotes you one, they are quoting their own fee, not Medicare’s.

CMS-855O — enrollment for the sole purpose of ordering and certifying

Section 6405 of the Affordable Care Act requires that the clinician who orders a home health episode, a DMEPOS item or a lab test be enrolled in Medicare — even when that clinician will never bill Medicare for anything. The 855O is how they get there.

The form lists who it is for, and the list is more specific than most people expect: clinicians employed by the Department of Veterans Affairs, the Department of Defense / Tricare, the Public Health Service, the Indian Health Service or a Tribal Organization, or by an FQHC, RHC or Critical Access Hospital; licensed residents in an approved medical residency program; dentists, including oral surgeons; pediatricians; and retired physicians who are still licensed.

Once enrolled, you appear in the CMS database as eligible to order and certify. You get no billing privileges and no PTAN for claims. This matters downstream in a way that is easy to miss: a home health agency’s claim can be denied because the ordering physician is not in that database — a problem the agency cannot fix from its own side. If you run an agency, verifying ordering clinicians is part of your intake, not part of your billing.

CMS-855S — DMEPOS suppliers

The 855S is its own world. It enrolls Durable Medical Equipment, Prosthetics, Orthotics and Supplies suppliers, and the list of who must file it is long and counter-intuitive — it includes pharmacies, grocery stores, department stores, opticians, physicians and dentists who furnish DMEPOS, physical and occupational therapists, sleep laboratories, hospitals, home health agencies and skilled nursing facilities among many others. If your organization hands a patient a covered item and bills Medicare for it, you are probably in scope even if “DME supplier” is not how you describe yourself.

Three things separate the 855S from every other 855:

• A $50,000 surety bond from an authorized surety, per NPI, effective on the date the application is submitted — with an elevated amount if the contractor requires it.
• Accreditation by a CMS-approved accrediting organization for each product line. Adding a product line after enrollment means being re-surveyed for it.
• A three-year revalidation cycle rather than five: 42 CFR 424.57(g) requires a supplier to revalidate its billing privileges every three years.

The application fee must also be paid in the calendar year you submit the 855S.

Scope note. Maverick handles credentialing, enrollment and payer contracting. DMEPOS accreditation and surety bonding are not services we sell — they are a different specialty with different vendors, and we will tell you that in the first conversation rather than the fourth. Where a DMEPOS line sits inside a practice we already serve, we sequence around it.

The two forms that ride along with all of them

CMS-588 — Electronic Funds Transfer Authorization. Medicare pays by EFT. The 588 goes in with your enrollment application along with a voided check or a bank letter. Every 855’s “tips to avoid delays” section names it, because leaving it out is a deficiency that stops an otherwise clean file.

CMS-460 — Medicare Participating Physician or Supplier Agreement. Optional, and it decides whether you accept assignment on all claims. It is a business decision about your fee schedule position, not a compliance step, and it has a filing window tied to your enrollment.

Effective dates: the part that decides whether you get paid

This is where enrollment stops being paperwork and starts being revenue.

For the provider and supplier types listed at 42 CFR 424.520(d) — physicians, non-physician practitioners, physician and non-physician practitioner organizations, ambulance suppliers, opioid treatment programs, Part B hospital departments, CLIA labs, intensive cardiac rehabilitation facilities, mammography centers, mass immunizers and pharmacies, radiation therapy centers, home infusion therapy suppliers, and physical therapists, occupational therapists and speech-language pathologists — the effective date of billing privileges is the later of:

1. the date you filed an enrollment application that was subsequently approved, or
2. the date you first began furnishing services at the new practice location.

And under 42 CFR 424.521, those same types may retrospectively bill for up to 30 days before that effective date when circumstances precluded enrolling in advance — extended to 90 days where a Presidentially-declared disaster under the Stafford Act did.

Now the asymmetry. Surveyed, certified and accredited providers get none of that. Their effective date is governed by 42 CFR 489.13, which turns on when they met all federal requirements — enrollment, the provider agreement, and the health and safety Conditions of Participation. An 855A applicant cannot file early and backdate its way to revenue. The only lever is starting sooner, which is why home health, hospice and SNF launches are planned backward from an intended open date rather than forward from an incorporation date.

DMEPOS suppliers are governed separately again, by 42 CFR 424.57(b), and their effective date can turn on the effective date of the surety bond.

Revalidation, and the fee that comes back

Under 42 CFR 424.515, providers and suppliers other than DMEPOS must resubmit and recertify the accuracy of their enrollment information every five years. DMEPOS suppliers revalidate every three. CMS contacts you directly when it is time — and every 855 warns you not to submit a revalidation application until your MAC has asked for it, because an unsolicited one is returned.

The CY 2026 application fee of $750 is owed again at revalidation for institutional providers, and also when you add a new practice location. It is paid through PECOS before the application is submitted. Applications arriving without the fee paid sit in a queue nobody is working.

Deactivation for failing to revalidate is not a pause. It ends billing privileges and requires a new application to restore them, with a new effective date and no retroactive window for certified providers. We keep clients ahead of the clock as part of recredentialing and maintenance, because the notice arrives at the address CMS has on file — which is often not the address anyone still checks.

So which form is yours?

Work down this list and stop at the first match:

• You are a person, and you will send claims to Medicare. → CMS-855I.
• You are a person, and you will only order or certify. → CMS-855O.
• You are an organization that will bill Part A and requires survey or accreditation (hospital, HHA, hospice, SNF, FQHC, RHC, CMHC, ESRD, CORF, OTP, and the rest of the certified list). → CMS-855A.
• You are an organization or supplier that will bill Part B (group practice, clinic, independent lab, portable x-ray, ASC reporting a CHOW, hospital department billing practitioner services). → CMS-855B.
• You will bill Medicare for equipment, prosthetics, orthotics or supplies. → CMS-855S.
• You are a practitioner joining a group. → CMS-855I for you, and the group files or has already filed a CMS-855B. Both must be enrolled before the reassignment is effective.

A group launching with several clinicians will file most of these at once, in a sequence where the group’s 855B has to clear before the practitioners’ reassignments can attach. That sequencing — not the forms themselves — is where launches slip, and it is exactly what group enrollment and contracting exists to manage.

The Medicare enrollment is not the finish line

Medicare enrollment produces Medicare billing privileges. It does not put you in a Medicare Advantage network, a Medicaid program, or any commercial plan. Medicare Advantage plans generally require Medicare enrollment as a precondition and then run their own credentialing on top. Medicaid is a separate application in every state — in Texas, that is TMHP and PEMS — followed by separate managed care contracts.

If you are mapping the whole sequence rather than a single form, start with credentialing vs. enrollment, which draws the line between being verified, being enrolled, and being contracted.

Get the form right the first time

Every week spent on the wrong 855 is a week your effective date moves. If you would rather have a specialist name the form, file it, and hold the deficiency correspondence, a 20-minute consult is where that starts — and you will get a written scope before anything is committed.

Sources: CMS-855A, CMS-855B, CMS-855I, CMS-855O and CMS-855S enrollment applications (CMS.gov); 42 CFR 424.515, 424.520, 424.521, 424.525 and 424.57 (eCFR); Medicare, Medicaid and CHIP; Provider Enrollment Application Fee Amount for Calendar Year 2026, 90 FR (Dec. 3, 2025). Verified 2026-08-12.