CMS Substantial Portion Rules for Physician-APP Teams
When a physician and an Advanced Practice Provider (APP), a nurse practitioner or physician assistant, both participate in the same patient visit, who bills the claim? Under CMS split/shared visit rules, the answer depends on who performed the "substantial portion" of the encounter, and since 2022, the rules have been significantly tightened. Getting this wrong is one of the fastest ways to trigger a Medicare audit.
A split/shared visit occurs when a physician and a qualified non-physician practitioner (NPP), an NP or PA, each personally perform a face-to-face portion of an E/M visit with the same patient on the same date of service, in a facility setting. The visit is then billed under one provider's NPI based on who performed the "substantial portion."
Split/shared rules apply only in facility settings, hospital inpatient, hospital outpatient, emergency department, observation, skilled nursing facility, and critical care. Office-based visits where the physician and APP see the same patient separately are governed by different rules (incident-to or direct billing).
CMS defines the substantial portion as the portion that determines who may bill the visit under their NPI. As of 2023 and continuing in 2026, the substantial portion is defined solely by time.
2026 rule: The provider who spends more than half (greater than 50%) of the total time spent by both providers on the visit is considered to have performed the substantial portion. That provider bills the claim under their own NPI.
Prior to this rule finalization, CMS had considered history, physical exam, or medical decision making (MDM) as alternative ways to define the substantial portion. Those alternatives are no longer in effect for Medicare split/shared visits; time is the only standard.
Total split/shared visit time includes the combined face-to-face and non-face-to-face time spent by both providers on the date of service, following the same E/M time counting rules (ordering tests, reviewing records, documentation, care coordination on the date of the visit).
| Scenario | Physician Time | APP Time | Who Bills? |
|---|---|---|---|
| APP does most of visit, physician briefly reviews | 8 min | 22 min | APP bills under own NPI |
| Equal contribution | 15 min | 15 min | Either may bill (document clearly) |
| Physician performs the majority | 25 min | 10 min | Physician bills under own NPI |
| Physician sees patient, APP documents only | 30 min | 20 min (documentation) | Physician bills: documentation time counts |
For a split/shared visit to be billed compliantly, the medical record must clearly support:
Co-signature is not documentation: A physician co-signing an APP's note doesn't constitute split/shared participation. The physician must independently document their own personal, face-to-face or non-face-to-face contribution to the visit on that date.
This is why split/shared rules matter so much financially. When a service is billed under the physician's NPI in a facility setting, Medicare pays at 100% of the physician fee schedule. When billed under the APP's NPI, Medicare pays at 85% of the physician fee schedule.
For a high-volume inpatient or hospitalist practice seeing 20 patients per day with a physician-APP team, the difference between correctly documenting physician substantial portion vs. defaulting to APP billing can represent $80,000–$150,000 in annual revenue difference per physician.
Split/shared rules don't apply to critical care services (99291/99292). Critical care must be billed under the provider who personally performed the critical care; there's no split/shared mechanism for critical care. Each provider bills only their own time, and physician and APP critical care time can't be combined.
Split/shared claims are reviewed for two things: does the record show what each provider did and for how long, and is the claim under the right NPI. Because the substantive portion is decided by time, a note without each provider's minutes can't support billing under the physician. A co-signature alone doesn't show participation.
The financial gap is why reviewers care. A facility visit billed under the physician pays at the full fee schedule, while the APP's own NPI pays 85 percent, so a pattern of billing under the physician without supporting time records is an overpayment on every claim. On a hospitalist group averaging 15 split/shared visits a day, a 3-year lookback with even a 20% error rate on the physician-NPI portion can put $90,000 to $140,000 in recoupment on the table, plus the cost of the appeal. Add a required time field for each provider to the split/shared note template, and make the modifier depend on it.
Because the substantive portion is decided by time, the note has to capture minutes. Add a time field for each provider to the split/shared template, with a prompt for what the time covered. Have both providers document on the same date. If the note is signed by one provider and attested by the other, the attestation should state the portion of the time the second provider personally performed.
Then confirm the claim. The billing team should compare the times in the note to the NPI on the claim, and hold the claim if it isn't clear who did more than half the work.
Some visits will be near the halfway mark. Decide in advance how the practice will handle them, and require that the note show both providers' minutes. If it's unclear, the safer choice is to bill under the provider whose time is clearly documented as the majority, or to use the APP's NPI.
By time. The article says the provider who spends more than half of the total time on the visit is the one who bills it, and total time follows the same rules as E/M time counting.
No. The article says critical care (99291 and 99292) can't be split or shared and has to be billed under the provider who personally performed it.
Both providers' participation. The article says each must personally document their portion of the visit, and a co-signature alone isn't sufficient.
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