Two clinicians see the same patient on the same day. One is a physician, one is a nurse practitioner, and both are in your group. The claim can only carry one E/M code and one provider. The answer depends on the setting first, then on who did the substantive portion, and then on whether the note proves it. Get any of those three wrong and the claim is either underpaid or exposed to recoupment.
What this covers
- Split or shared billing exists only in facility settings. In the office, incident-to rules apply instead.
- The substantive portion is more than half of the combined time, or a substantive part of the medical decision making.
- Time both clinicians spend together counts once, not twice. That single rule decides most disputes.
- The note must name both clinicians and state who performed the substantive portion. A countersignature is not enough.
- Modifier FS goes on the E/M code whenever the visit is billed as split or shared, whichever clinician bills.
A countersignature is not a substantive portion.The signature proves the physician read the note. It does not prove the physician did the work that earns the higher rate.
This is written for the billing manager who finds a physician signature on an APP’s note and has to decide whether the claim can go out under the physician’s NPI. The rules are federal, they are stable, and most of the errors come from applying the office rule in a hospital or the hospital rule in an office.
The setting decides which rulebook applies
A split or shared visit is an E/M service in a facility setting performed in part by a physician and in part by a nonphysician practitioner in the same group, where either one could have billed the service alone. The definition only makes sense where Medicare prohibits payment for services furnished incident to a physician’s professional services. That prohibition is what creates the need for a separate rule.
The office is not one of those places. In a physician office, the APP’s work is billed incident to the physician, under the physician’s NPI, at the full fee schedule rate. No modifier FS is involved. Applying split or shared logic to an office visit, or incident-to logic to a hospital visit, is the first and most expensive mistake in this area.
| Setting | Place of service | Rule that governs | Modifier |
|---|---|---|---|
| Hospital inpatient | 21 | Split or shared | FS on the E/M code |
| Hospital outpatient, on campus | 22 | Split or shared | FS on the E/M code |
| Hospital outpatient, off campus | 19 | Split or shared | FS on the E/M code |
| Emergency department | 23 | Split or shared | FS on the E/M code |
| Skilled nursing facility | 31 | Split or shared, unless the visit must be physician-only | FS on the E/M code |
| Nursing facility | 32 | Not billable as split or shared | None |
| Physician office | 11 | Incident to, 42 CFR 410.26 | None specific to incident-to |
Two exclusions sit inside the facility rule. Some skilled nursing facility visits must be performed directly and solely by a physician under the conditions of participation, and those cannot be split or shared. A resident is not an NPP for this purpose either: encounters involving residents follow the teaching physician rules, which require the teaching physician’s personal participation in the key portion of the service.
The same group requirement is narrower than it looks. CMS has not published a definition of group, and its guidance says a physician and an NPP must work jointly on the whole of the E/M service. A hospital-employed APP and a physician in an independent group do not form a split or shared pair. Each bills separately for what each furnished. The medical coding rules behind the visit level still apply to both claims.
What the substantive portion means now
Since January 1, 2024, CMS defines the substantive portion in two ways, and the billing practitioner has to satisfy one of them. The first is more than half of the total time the physician and NPP spent on the visit. The second is a substantive part of the medical decision making, as the CPT guidelines describe it. CMS retained that definition for 2026, and 42 CFR 415.140 still reads the same way.
The time route is arithmetic once the time is written down. Add the physician’s time and the NPP’s time. Where they met the patient together, or discussed the case together, count that shared block once, not twice. Whoever holds more than half of the total bills the visit. The Medicare Administrative Contractor’s own example makes the counting concrete: the NPP spends ten minutes, the physician spends fifteen, so the physician has fifteen of twenty-five minutes and bills. If the two then spend five more minutes together on the plan, the total becomes thirty minutes and the physician holds twenty of them, which is still more than half.
Qualifying time follows the CPT list. Preparing to see the patient, reviewing tests, taking or reviewing history, examining the patient, counseling, ordering, referring, documenting, interpreting results and care coordination all count, whether or not the patient is present. Time spent on separately reported services, travel, and general teaching does not count.
The MDM route is judgment, not arithmetic. The billing practitioner has to make or approve the management plan for the number and complexity of problems addressed, and take responsibility for the treatment plan and its risk. Reviewing someone else’s assessment and agreeing with it is not the same act. When the note reads as one clinician’s thinking with a second signature under it, the MDM route is not supported.
Critical care and prolonged services do not use MDM, so the substantive portion for those is more than half of the total time, full stop. For critical care, the cumulative critical care time furnished by both clinicians on the calendar date is summed, and the clinician with more than half reports 99291 and any 99292 units.
One clinician must have face-to-face contact with the patient, but it does not have to be the physician, and it does not have to be the clinician who bills. The time and MDM comparison is the same test that sets the visit level, so both questions get answered in one pass.
Documentation that proves who did the work
The regulation sets two documentation conditions. The record must identify the physician and the NPP who performed the visit, and the individual who performed the substantive portion must sign and date it. Those are the minimum. An auditor reading the note also needs to see which basis was used and where the numbers came from.
A defensible split or shared note carries four things:
- Both clinicians named in the body of the note, with the part each performed.
- The basis stated in words: substantive portion of MDM, or more than half of total time.
- The time, when time is the basis: each clinician’s minutes, the shared minutes, and the total.
- A signature and date from the clinician who performed the substantive portion, in that clinician’s own attestation.
The weakest version of this note is a single paragraph written by the APP with the physician’s signature at the bottom and nothing in between. The signature satisfies the authentication requirement and fails the substantive portion requirement at the same time. A short addendum is enough when it is specific: what the physician personally reviewed, what was changed in the plan, and the minutes involved if time is the basis.
The level of service is selected from the combined documentation of both clinicians, not from the physician’s addendum alone. A level 4 visit supported only by the APP’s history and exam is still a level 4 claim under the physician’s NPI if the physician performed the substantive portion. The record has to support the code, and the record is the whole note.
Modifier FS and the rest of the claim
Modifier FS identifies a split or shared E/M visit and goes on the E/M code. It is required whichever clinician bills, and its absence on a qualifying claim is a reporting error in its own right. Modifier 52 is not a substitute. Medicare does not pay for partial E/M visits, and 52 describes a reduced service, not a shared one.
The other modifiers on the claim answer different questions. Modifier 25 marks a significant, separately identifiable E/M service on the same day as a procedure. Modifier FT marks critical care unrelated to a procedure during a global surgical period. Neither one identifies a split or shared visit, and stacking them does not cure a missing FS.
Payment follows the billing clinician. A physician billing a split or shared visit is paid at 100 percent of the fee schedule. An NPP billing the same visit is paid at 85 percent. That gap is the entire financial reason groups build the workflow, and it is also the reason a claim billed under a physician’s NPI without a documented substantive portion draws attention.
Same-day rules still apply on top of all this. Physicians in the same group and the same specialty are treated as a single physician for payment, so two E/M visits on the same date collapse into one claim at the combined level unless the services were for unrelated problems. Critical care is the exception that allows a separate E/M earlier in the day, with modifier 25 and documentation that the earlier visit was furnished before the patient required critical care. The critical care coding rules cover that split in detail.
In the office, incident-to replaces split or shared
Office visits run on a different rule with different failure points. Incident-to billing lets the practice report the physician’s NPI at 100 percent for work the APP performed, provided four conditions hold: the patient is established, the service is part of a plan of care the physician established and maintains, the physician provides direct supervision, and the APP is acting as auxiliary personnel under the physician’s employment or contract.
Direct supervision changed on January 1, 2026. CMS made virtual direct supervision permanent for services that require it, including most incident-to services, through real-time two-way audio and video. Audio-only does not qualify, and services with a global surgery indicator of 010 or 090 still require physical presence. The supervising physician has to be immediately available to intervene, which is a higher bar than being reachable by message.
The established patient condition does the most damage in practice. A new patient seen by an APP cannot be billed incident to, and neither can an established patient with a new problem that the physician has not yet addressed in a plan of care. Those visits go out under the APP’s own NPI at 85 percent. Groups that bill everything under the physician discover the pattern in an audit, because the new-patient claims are the ones that cannot be explained.
State scope of practice sits underneath both rulebooks. An APP who cannot legally furnish a service without a physician’s involvement cannot bill it independently either, and the federal rule does not create authority that state law withholds.
Where the money leaks, and how to find it
Most split or shared errors are not coding errors. They are handoff errors between the two clinicians, recorded after the fact by someone reconstructing the visit from the schedule. A monthly sample of ten claims billed with FS will show whether the workflow holds.
Include at least two where the NPP billed, since the 85 percent rate raises a different question about whether the NPP really held the substantive portion.
Write down who you think performed the substantive portion and on what basis before you check what was billed. The gap between the two answers is the finding.
Add each clinician’s minutes and the shared minutes once. If the note gives only a total, the claim cannot be defended on time.
FS present, billing NPI matches the clinician who held the substantive portion, and the place of service is a facility code.
Look for a second E/M on the same date by the same group and specialty, and confirm the unrelated-problem exception or the combined level.
| What the claim shows | What it usually means | Fix |
|---|---|---|
| Physician NPI, no FS | Office staff billed incident-to logic in a facility | Add FS and confirm the substantive portion, or rebill under the NPP |
| FS on an office claim | Hospital rule applied in a physician office | Remove FS and test the incident-to conditions |
| FS present, note names one clinician | The second clinician’s involvement was never documented | Addendum with the specific work performed, if it can be supported |
| Time totals that exceed the visit | Shared minutes counted twice | Recalculate with shared time counted once |
| NPP billed at 100 percent | Claim priced as if the physician billed | Correct the expected rate, then check the contract |
| New patient billed incident to | Established patient condition not met | Rebill under the NPP’s NPI at 85 percent |
The repair for a claim already paid is a corrected claim, and it only works when the documentation supports the corrected version. A note that cannot show who did what cannot be fixed by a modifier. That is the argument for building the attestation into the template rather than asking clinicians to remember it. Medical coding and billing teams that put the four required elements in a smart phrase get a usable note on the first attempt.
Split and shared visit questions
No. The physician has to perform the substantive portion, which means more than half of the combined time or a substantive part of the medical decision making. A signature authenticates the record and proves nothing about the work. If the physician reviewed the note, agreed with the plan and spent two minutes doing it, the visit belongs under the APP’s NPI at 85 percent.
No. Split or shared visits exist only in facility settings, where payment for services incident to a physician’s professional services is prohibited. Office visits use the incident-to rule at 42 CFR 410.26, which requires an established patient, a physician’s plan of care and direct supervision. Modifier FS does not belong on an office claim.
Modifier FS, on the E/M code, whichever clinician bills the visit. It is required for Medicare and for most commercial payers that follow the Medicare rule. Modifier 52 is not a substitute because Medicare does not pay for partial E/M visits. Modifiers 25 and FT answer separate questions about same-day and global-period services.
The shared time counts once. Add the physician’s solo time, the NPP’s solo time and the joint time, counting the joint block a single time, then compare each clinician’s share to the total. If the NPP spent ten minutes, the physician fifteen, and they spent five together, the total is thirty minutes and the physician holds twenty, which is more than half.
Yes, but on time alone. Critical care does not use medical decision making for code selection, so the substantive portion is more than half of the cumulative critical care time both clinicians furnished on that calendar date. The clinician with more than half reports 99291 and any 99292 units, and modifier FS goes on those codes.
One of the two clinicians must have face-to-face contact with the patient, and it does not have to be the physician or the one who bills. The substantive portion can be entirely non-face-to-face, such as reviewing imaging and setting the plan. What matters is the proportion of total time or the substance of the decision making, not who stood at the bedside.
The bottom line
The rules are not complicated once the setting is settled: facility visits use the substantive portion test and modifier FS, office visits use incident-to. Almost every error traces back to one of those two rulebooks being applied in the wrong place, or to a note that never recorded who did the work. A template that asks for the four documentation elements costs nothing to build and settles the question at the point of care.
How many FS claims would survive a chart review?
MedFactor audits split or shared claims against the note, recalculates the time, and checks the modifier and billing NPI together. Send us ten recent FS claims and we will show you which ones rest on a documented substantive portion and which ones rest on a signature.
Request a free coding reviewThis article summarizes CMS regulations, Medicare manual guidance and MAC publications as of November 2026 and is not legal or compliance advice; confirm the current rule and your payer contracts before changing a billing workflow.
