Overview
Modifier FS carries the CMS descriptor "split (or shared) evaluation and management visit". It exists because Medicare lets a physician and a nonphysician practitioner, such as a nurse practitioner or physician assistant, who are in the same group combine their work on one E/M visit in a facility, as long as the visit could have been billed by either of them alone. Chapter 12, section 30.6.18 of the Medicare Claims Processing Manual defines the visit, sets the billing rule and requires FS on the claim so the payer can see that two practitioners contributed.
The setting limits come first. Split or shared visits are furnished only in facility settings, meaning institutional settings where Medicare does not allow billing incident to a practitioner's services, such as hospitals and skilled nursing facilities. Office visits and nursing facility visits are not billable as split or shared, and SNF visits that the conditions of participation require a physician to perform entirely cannot be split either. New and established patients, and initial and subsequent visits, all qualify when the other conditions are met.
The billing practitioner is whoever performed the substantive portion. Since January 1, 2024 that means more than half of the total time the two spent on the visit, or a substantive part of the medical decision making as the CPT E/M guidelines define it. Critical care and prolonged services, which have no medical decision making component, use time only. The choice matters financially because Medicare generally pays services billed by a nurse practitioner or physician assistant at 85 percent of the physician fee schedule amount, so the documentation decides both who bills and what is paid.
The record must name the physician and the NPP who performed the visit, and the practitioner who performed the substantive portion, and therefore bills, must sign and date it. The manual adds two reminders: modifier 52 cannot be used to report a partial E/M visit, because Medicare does not pay for partial visits, and FS itself does not change the payment amount. In practice, audits of split or shared billing focus on whether the time or decision-making notes support the billing practitioner, so time stamps for each practitioner's work and an explicit statement of who made the key decisions are the safeguards. Split or shared billing is also separate from incident-to billing: in the office, where incident-to rules apply, a physician can bill a nonphysician practitioner's follow-up visit only when the incident-to conditions are met, and FS is not used.
Worked example
A hospitalist and a physician assistant in the same group see an inpatient on day two of a stay. The physician assistant spends 20 minutes reviewing results and examining the patient; the hospitalist spends 25 minutes, revises the treatment plan and talks with the family. The hospitalist performed more than half of the 45 minutes, so the subsequent hospital visit is billed under the hospitalist's NPI with modifier FS, and both practitioners are named in the signed note.
Look it up in CMS data
Free reference pages and tools rebuilt from the current CMS release files, for looking up the CMS data behind this term.
Frequently asked questions — Modifier FS (Split or Shared E/M Visit)
When is the FS modifier required?
Whenever a physician and a nonphysician practitioner in the same group each perform part of one E/M visit in a facility setting and the visit is billed as a split or shared service. The manual requires FS on those claims so the payer can identify them.
Can split or shared visits be billed in the office?
No. Medicare limits split or shared visits to facility settings where incident-to billing is not allowed, such as hospitals and skilled nursing facilities. Office and nursing facility visits are not billable as split or shared.
Who bills a split or shared visit?
The practitioner who performed the substantive portion: since 2024, more than half of the combined time or a substantive part of the medical decision making. For critical care and prolonged services only time counts.
Does modifier FS change the payment?
Not by itself. The payment follows the billing practitioner: Medicare generally pays NPP-billed services at 85 percent of the physician fee schedule amount, so the substantive-portion decision is what changes the amount paid.
Disclaimer
This glossary entry is operational reference for revenue-cycle and medical-billing professionals. It is not legal, clinical, or contractual advice. Industry benchmarks cite named public sources where available; always verify against the current guidance from the authority body before relying on a number in a contract, policy, or compliance filing.