Split/Shared E/M: The Substantive Portion

When a physician and a nurse practitioner both contribute to the same hospital encounter, exactly one of them bills it — and the rule for deciding which one changed materially in 2024. The current test asks who performed the substantive portion, defined as more than half of the total time or the substantive part of the medical decision making. Get it wrong and the claim is billed under the wrong national provider identifier, which is a payment error rather than a documentation quibble.

This page covers the definition, the setting boundary that separates split/shared billing from incident-to billing, the substantive-portion test as it now stands, the required modifier, and what the medical record has to show.

Verified against Noridian Healthcare Solutions, Jurisdiction E Part B, “Split or Shared Services,” last updated 21 July 2025; the American College of Surgeons, “Reporting Split/Shared E/M Visits in 2024”; 42 CFR 415.140 (conditions for payment: split (or shared) visits); 42 CFR 410.26 (incident to physician’s professional services); and the Medicare Claims Processing Manual, Publication 100-04, Chapter 12, Section 30.6.18. CPT codes and descriptions are copyright the American Medical Association.

What a Split (or Shared) Visit Is

Noridian’s definition: a split or shared visit “means an evaluation and management visit in the facility setting that is performed in part by both a physician and a nonphysician practitioner who are in the same group, in accordance with applicable law and regulations such that the service could be billed by either the physician or nonphysician practitioner if furnished independently by only one of them.”

Four conditions are packed into that sentence:

It is an E/M visit.
It is in a facility setting.
It is performed in part by both a physician and a non-physician practitioner (NPP).
Both are in the same group, and either could have billed the service independently.

Noridian adds that the “work provided may be both face-to-face and non-face-to-face,” and that “payment is made to the practitioner who performs the substantive portion of the medical decision making (MDM) or total time for the visit.”

Per the American College of Surgeons, a split/shared E/M visit “may be provided to a new or established patient for an initial or subsequent visit.” There is no new-versus-established restriction.

The Setting Boundary: Split/Shared Versus Incident-To

This is the most consequential distinction in the whole area, and the ACS puts the question and answer directly.

Can a split/shared E/M visit be reported in a non-facility setting? “No. This new split/shared E/M visit reporting policy applies only to those furnished in a facility setting. In a non-facility setting, such as a physician’s office, different reporting rules apply when an NPP provides some or all of an E/M visit and the physician bills for the visit. This type of E/M visit is referred to as an ‘incident-to’ service.”

So the setting determines the framework:

Facility setting — hospital or other facility: split/shared rules, governed by 42 CFR 415.140, decided by substantive portion, reported with modifier FS.
Office (non-facility) setting: incident-to rules, governed by 42 CFR 410.26, with an entirely different set of supervision and establishment-of-plan conditions.

Practices that operate in both settings sometimes apply one framework everywhere. That produces incorrect billing in whichever setting was not the source of the habit. Our guide to incident-to billing and its conditional test, setting by setting covers the office-side rules in detail.

Who Counts as an NPP

Per the ACS: “Medicare defines an NPP as a nurse practitioner, physician assistant, certified nurse specialist, or certified nurse midwife. All of these practitioners may independently report E/M services if they are legally authorized and qualified to furnish an E/M service in their state.” NPPs caring for Medicare patients in a facility “must enroll in the Medicare program to bill for the services they provide.”

On “same group,” the ACS notes that CMS “has yet to provide a definition of ‘same group’ at this time, but has indicated that a physician and an NPP must work jointly to furnish all of the work related to the E/M in circumstances when a split/shared visit is appropriately billed.” Where the physician and NPP are in different groups, “the physician and NPP would be expected to bill independently and only for the services each fully furnishes.”

The Substantive Portion Test

Per Noridian, for CY 2024 the CMS definition of substantive portion “includes the revisions to the CPT guidelines.” The substantive portion means:

“More than half of the total time spent by the physician or nonphysician practitioner performing the split or shared visit, OR
The substantive part of the medical decision making”

Noridian states the resulting flexibility plainly: “Medicare will allow time or medical decision making to serve as the substantive portion of a split or shared visit.”

The ACS quotes the CPT guidance CMS adopted, and this is the part practices most need to internalise:

“For the purpose of reporting E/M services within the context of team-based care, performance of a substantive part of the MDM requires that the physician(s) or other QHP(s) made or approved the management plan for the number and complexity of problems addressed at the encounter and takes responsibility for that plan with its inherent risk of complications and/or morbidity or mortality of patient management. By doing so, a physician or other QHP has performed two of the three elements used in the selection of the code level based on MDM.”

Two things follow. Making or approving the management plan, and taking responsibility for it, is what constitutes the substantive part of MDM — not merely reviewing the note or countersigning it. And doing so is credited as performing two of the three MDM elements.

If code selection is based on total time, the ACS states the service “is reported by the professional who spent the majority of the face-to-face or non-face-to-face time performing the service.”

Critical Care Is Different

Noridian flags the exception: “For critical care visits, starting for services furnished in CY 2022, the substantive portion will be more than half of the total time.” Critical care does not get the MDM option. Time is the only test, and it has been that way since 2022.

What the Transitional Years Looked Like

Practices auditing older claims need the prior rule. Per Noridian: “During the transitional years, 2022 and 2023, except for critical care visits, the substantive portion can be one of the three key E/M visit components (history, exam, or medical decision-making [MDM]), or more than half of the total time spent by the physician and NPP performing the split or shared visit. When one of the three key components is used as the substantive portion in 2022 and 2023, the practitioner who bills the visit must perform that component in its entirety to bill.”

That “in its entirety” requirement is stricter than the current MDM test, and a claim from 2022 or 2023 should be assessed against it rather than against today’s rule.

Modifier FS and the Documentation Requirements

Noridian: “Append modifier FS (Split or Shared E/M Visit) to the E/M code to report these services.” The modifier is not optional, and its absence on a qualifying facility claim is itself a reporting error. The ACS confirms CMS requires modifier FS “no matter if the physician or” NPP bills the service.

On the record: “The provider performing the substantive portion will submit the appropriate level of E/M service under their name and NPI number. The medical record must identify both providers involved in the split or shared E/M service and be signed by the billing provider.”

Noridian lists what documentation must include:

Identity of both providers who perform the visit
Who performed the substantive portion of the visit

That second item is the one most often missing. A note signed by both clinicians, with no statement identifying who performed the substantive portion, does not establish that the billing NPI is the correct one.

Worked Example One: MDM Decides It

A patient is admitted overnight with a COPD exacerbation. The following morning an NPP sees the patient first, takes the interval history, examines the chest, reviews the overnight observations and the morning blood gas, and drafts an assessment. The attending physician then sees the patient, confirms the findings, decides to escalate to intravenous corticosteroids and add an antibiotic, and documents that plan and the reasoning behind it. The NPP spent roughly 30 minutes; the physician spent roughly 15.

Report: under the physician’s name and NPI, with modifier FS appended.

Why: the physician did not spend more than half the total time — the NPP did. But the physician made the management plan for the problems addressed and took responsibility for it, which is the substantive part of MDM. Because CMS permits either time or MDM to serve as the substantive portion, the MDM route governs and the physician bills.

What the note must say: both clinicians identified, and an explicit statement that the physician performed the substantive portion by making the management plan.

Worked Example Two: Time Decides It

The same admission, next day. The NPP conducts the entire encounter: interval history, examination, review of results, and formulation of the plan to continue current therapy and plan discharge. The physician briefly reviews and agrees, spending about five minutes, and contributes no change to the plan.

Report: under the NPP’s name and NPI, with modifier FS.

Why: the NPP performed the majority of the time and made the management plan. A brief physician review that neither drives the plan nor takes responsibility for it is not the substantive part of MDM. Billing this under the physician’s NPI because the physician is the attending is the classic error this rule exists to prevent.

Worked Example Three: Wrong Framework

In a hospital-owned physician office, an NPP sees an established patient for a stable chronic condition, and the supervising physician is in the suite but does not see the patient.

Split/shared does not apply — this is a non-facility office setting. The applicable framework is incident-to under 42 CFR 410.26, with its own conditions on supervision and on whether the physician established the plan of care. Modifier FS has no role here.

Frequently Asked Questions

Is modifier FS required on every split/shared claim?

Yes. CMS requires modifier FS on the E/M code for split or shared visits, regardless of whether the physician or the NPP is the billing practitioner.

Can the physician bill if the NPP spent more time?

Yes, provided the physician performed the substantive part of the MDM — made or approved the management plan for the number and complexity of problems addressed and took responsibility for it. Since CY 2024, time and MDM are alternative routes, not cumulative requirements.

Does countersigning the NPP’s note make the physician the billing provider?

No. The substantive part of MDM requires making or approving the management plan and taking responsibility for it. A signature attesting to review does not by itself meet that description, and it does not establish more than half the total time either.

Does either practitioner have to see the patient face to face?

The work “may be both face-to-face and non-face-to-face.” Contractor guidance in this area generally expects a face-to-face encounter by one of the two practitioners, though not necessarily by the one who bills. Check your own MAC’s published position, which is where this detail is settled.

Do split/shared rules apply in the emergency department and skilled nursing facilities?

The policy applies to E/M visits in a facility setting, which covers institutional environments rather than the physician office. Where a specific visit type has its own instruction — critical care being the clearest example, with its time-only test — that instruction governs.

What about 2022 and 2023 claims?

Assess them under the transitional rule: one of the three key components performed in its entirety, or more than half the total time. Applying today’s MDM test retrospectively will produce the wrong answer on claims from those years.

Where is this written down?

42 CFR 415.140 sets the conditions for payment for split (or shared) visits; the Medicare Claims Processing Manual, Pub. 100-04, Chapter 12, Section 30.6.18 carries the operational instruction; and 42 CFR 410.26 governs the incident-to alternative in the office setting.