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Modifiers 62 and 66 answer a question no other modifier in the surgical set addresses: how many surgeons the operation genuinely required, and in what relationship. Everything else in the global-surgery family describes timing or scope. These two describe personnel, and they are the ones most likely to be denied for a reason that has nothing to do with the operative note.
That reason is a number in the fee schedule database that most claims never consult. CMS has already decided, code by code, whether two surgeons or a team are plausibly necessary for that procedure. If the indicator says no, the second claim denies regardless of what happened in theatre. If it says "documentation required," the claim suspends for manual review and nothing pays until a human reads the report. Checking the indicator before the case is the single highest-value habit in this area.
The Decision Rule
Chapter 12 of the Medicare Claims Processing Manual (Publication 100-04), Section 40.8, sets out the framework. It opens with the premise that matters: under some circumstances the individual skills of two or more surgeons are required on the same patient during the same operative session, because of the complexity of the procedure or the patient’s condition — and in these cases the additional physicians are not acting as assistants-at-surgery. That sentence is the boundary between this guide’s modifiers and the assistant set, which has its own guide: modifiers 80, 81, 82 and AS.
Modifier 62 — co-surgeons
- Two surgeons, each in a different specialty, were required to perform a specific procedure. Co-surgery also covers procedures where two surgeons perform parts of the procedure simultaneously — the manual gives heart transplant and bilateral knee replacement as examples.
- Each surgeon bills the same procedure code with modifier 62. Both claims must carry it. Contractor guidance warns that if only one does, that physician is paid at 100 percent and the other physician’s claim denies.
- The fee schedule co-surgery indicator (Field 24 of the fee schedule database) must permit it — see below.
- The procedure code and diagnosis code should match across the two claims, though the billed amounts need not.
Modifier 66 — surgical team
- A team of more than two surgeons of different specialties was required for a specific procedure. Contractor guidance describes the setting: a single, highly complex procedure requiring several physicians from the same or different specialties, along with other highly skilled and specially trained personnel and complex equipment — usually confined to organ transplant teams.
- Every surgeon appends modifier 66 to the code.
- The team surgery indicator (Field 25) must permit it.
- The claim must carry enough information to allow pricing "by report." The manual states this as an absolute: all claims for team surgeons must contain sufficient information to allow by-report pricing.
The case that is neither
Section 40.8.B closes with a scenario that trips up a lot of multi-specialty operating: if surgeons of different specialties are each performing a different procedure, with specific CPT codes, neither co-surgery nor multiple-surgery rules apply — even if the procedures are performed through the same incision. Each surgeon simply bills their own procedure. If one of them performs multiple procedures, the multiple-surgery rules apply to that surgeon’s services only. Two surgeons in the same field at the same time is not automatically co-surgery; co-surgery means both are working on the same code.
The Indicators That Decide Whether Anything Pays
Section 40.8.C tells contractors exactly what to do with each indicator value, and the behaviour differs enough to be worth tabulating.
| Indicator | Modifier 62 (Field 24) | Modifier 66 (Field 25) |
|---|---|---|
| 0 | Payment adjustment rules for two or team surgeons do not apply. The MAC pays the first bill submitted, at the lower of the billed amount or 100 percent of the fee schedule amount, and denies bills received subsequently from other physicians. These are medical necessity denials. | |
| 1 | Claim suspends for manual review of documentation submitted with it. If the documentation supports the need for co-surgeons, each physician is paid at the lower of the billed amount or 62.5 percent of the fee schedule amount. | Claim suspends for manual review. If team surgeons are determined medically necessary, each physician is paid by report. |
| 2 | Payment rules for two surgeons apply. Each physician is paid at the lower of the billed amount or 62.5 percent of the fee schedule amount. | Paid by report. |
Two consequences follow that are easy to miss. First, on an indicator-0 code the order of submission decides who gets paid — the first bill in is paid at 100 percent and the second denies. That is a race condition, not a clinical judgment, and it is a reason for two practices to agree the billing approach before the case rather than after the denial. Second, on indicator-1 codes the manual specifies that documentation of medical necessity is required for certain services identified in the fee schedule database, so submitting the operative report with the claim rather than waiting for a request is the difference between a suspension that resolves and one that denies.
Section 40.8.C adds two operational rules that matter downstream. Contractors must apply the rules of global surgical packages to each of the physicians participating in a co- or team surgery — so each co-surgeon carries their own global period and may need modifier 58, 78 or 79 on later work. And contractors must retain the 62 and 66 modifiers in history, which is what makes co-surgery patterns visible to data analysis over time.
There is also a note on modifier 66 worth knowing before billing one: a Medicare fee may already exist for some procedures billed with modifier 66, and in those cases all physicians on the team must agree on the percentage of the payment each is to receive. If a contractor receives a modifier 66 claim after already paying one surgeon the full amount on an unmodified bill, it denies the subsequent claim.
What the Record Must Show
The operative report is doing two distinct jobs here: establishing that more than one surgeon was necessary, and establishing what each of them actually did.
- A statement of why two surgeons or a team were required — the complexity of the procedure, the patient’s condition, or both. This is what an indicator-1 manual review is looking for.
- Distinct, attributable operative work for each surgeon. Contractor guidance illustrates a spinal case where one surgeon performed the approach, the discectomy, the fusion preparation and the closure, while the other removed a ligament and end plates and placed and trimmed the graft. Two surgeons who both simply "participated" look like a surgeon and an assistant.
- Different specialties, evident on the face of the claims. Modifier 62 as the manual describes it turns on the two surgeons being in different specialties.
- Separate operative reports, or one report signed by both. Each surgeon’s contribution needs to be traceable to that surgeon, because each is billing the same code.
- For modifier 66, enough detail to price by report — a by-report claim without a report has nothing to price against.
- Agreement between the two practices. Because both claims must carry modifier 62 and generally the same diagnosis, the coding decision has to be coordinated across two billing offices. This is the most common practical failure point and it is administrative, not clinical.
The Misuse That Triggers Denials and Audits
- Reporting an assistant as a co-surgeon. The manual’s own framing forecloses it: in a genuine co-surgery the additional physician is not acting as an assistant-at-surgery. Co-surgery pays 62.5 percent each; assistant-at-surgery pays 16 percent. The incentive to mischaracterise is obvious and so is the audit interest.
- Modifier 62 where each surgeon performed a different procedure. Not co-surgery, even through the same incision. Each bills their own code.
- One-sided modifier 62. If only one surgeon appends it, the other’s claim denies. This is not recoverable by argument; it is recoverable by correcting the claim.
- Modifier 66 for two surgeons. Contractor guidance names this as incorrect use — modifier 66 is only appropriate for teams of three or more.
- Ignoring the indicator. On an indicator-0 code, the second claim denies as a medical necessity denial no matter how good the documentation is. Checking Field 24 or 25 before the case takes seconds; appealing afterwards does not.
- Billing team surgery without a report. By-report pricing requires a report.
What happens on a denial, and who pays
Section 40.8.D sets out the remittance handling, and it is unusually specific. Where a procedure is subject to the statutory restriction against payment for assistants-at-surgery, payment is denied with Group Code CO, CARC 54, and Medicare Summary Notice message 15.11, and contractors add the message "You cannot be charged for this service." Where Field 23 of the fee schedule database carries an indicator of 0 or 1 — meaning an assistant-at-surgery is not generally medically necessary for that procedure — the denial carries Group Code CO, CARC 54 and MSN 15.12. For indicator-0 procedures the limitation of liability provisions in Chapter 30 apply to assigned claims, so the appropriate limitation-of-liability language is included; for unassigned claims the Program Integrity Manual rules on medical necessity denials apply.
Group Code CO means the provider absorbs the cost, which is the practical meaning of "you cannot be charged for this service." Where a beneficiary might reasonably be asked to accept liability for a service Medicare is expected to deny, that is an ABN question — see modifier GA and the GX, GY and GZ decision matrix — and it has to be handled before the service, not after the denial.
Modifiers 62 and 66 vs. the Assistant-at-Surgery Set
This is the differentiation that decides the money, and it rests on a single question: was the second physician performing the surgery, or assisting the surgeon who was?
| Role | Modifier | Payment basis |
|---|---|---|
| Two surgeons, different specialties, same procedure code | 62 | 62.5 percent of the global surgery fee schedule amount, to each |
| Team of more than two surgeons of different specialties | 66 | By report |
| Physician assistant-at-surgery | 80, 81, 82 | 16 percent of the amount otherwise applicable for the surgical payment |
| PA, NP or CNS as assistant-at-surgery | AS | 80 percent of the lesser of the actual charge or 85 percent of the physician rate — which works out to 13.6 percent of the amount paid to physicians |
Section 20.4.3 sets the assistant-at-surgery rate at 16 percent of the amount otherwise applicable for the surgical payment, and adds a constraint that catches practices out: MACs may not pay assistants-at-surgery for surgical procedures in which a physician is used as an assistant in fewer than five percent of cases for that procedure nationally, determined through manual review. Procedures billed with 80, 81, 82 or AS are subject to assistant-at-surgery policy, and claims are paid only where an assistant is authorised for that procedure.
The section also carries a warning with teeth. Medicare’s rules on billing patients in excess of the allowed amount apply to assistant-at-surgery services, and physicians who knowingly and willfully bill a beneficiary for an assistant-at-surgery service on a restricted procedure may face penalties under section 1842(j)(2) of the Social Security Act, varying with the frequency and seriousness of the violation.
On the AS side, Sections 110.2 and 120.1 confirm the arithmetic separately for physician assistants and for nurse practitioners and clinical nurse specialists, and both state that the AS modifier must be reported when billing those services — Section 120.1 adding that only the AS modifier is reported for NP and CNS assistant-at-surgery services.
Modifier 62 vs. modifier 51
Different questions entirely, and the manual keeps them apart deliberately. Modifier 51 addresses one surgeon performing several procedures. Modifier 62 addresses several surgeons performing one. Where surgeons of different specialties each perform a different procedure, Section 40.8.B says neither co-surgery nor multiple-surgery rules apply — but if one of those surgeons performs multiple procedures, the multiple-surgery rules attach to that surgeon’s services alone.
Modifiers 62 and 66 vs. the global-period modifiers
Orthogonal. Modifiers 62 and 66 describe who operated; 58, 78 and 79 describe when and why. Because the global surgical package rules apply to each participating physician, a co-surgeon returning to theatre days later faces exactly the same 58-versus-78-versus-79 decision as a solo surgeon would.
A Working Sequence
- Before the case, look up the procedure code’s co-surgery indicator (Field 24) or team surgery indicator (Field 25).
- If the indicator is 0, expect only one payment. Decide, between the practices, what to bill and how to handle the second physician’s work.
- If the indicator is 1, plan to submit the operative report with the claim, not after it.
- Confirm the relationship: are both surgeons performing the same procedure code, or is one assisting, or are they performing different procedures?
- Confirm the specialties differ, and that the count matches the modifier — two for 62, more than two for 66.
- Coordinate across both billing offices so the modifier, the code and the diagnosis match.
- Track each surgeon’s own global period from the date of surgery.
Where Jurisdiction Matters
The 62.5 percent co-surgery rate, the by-report treatment of team surgery, the 16 percent assistant rate, the 13.6 percent AS figure and the indicator behaviour are all national and come from the Claims Processing Manual. The indicators themselves are not stable: co-surgery, team surgery and assistant-at-surgery indicator assignments are set per code in the Physician Fee Schedule and change with each annual release. A code that supported co-surgery last year may not this year, and that is the most common cause of a denial on a procedure a practice has billed successfully before.
MAC operational guidance differs in emphasis — Noridian, Novitas and First Coast Service Options all publish co-surgery pages and they do not read identically, particularly on what documentation is requested up front. Commercial and Medicare Advantage payers set their own co-surgery and assistant policies, and many use different percentages or require prior authorisation for a second surgeon; a plan is entitled to pay co-surgeons at a rate other than 62.5 percent. Verify against the payer’s own policy rather than assuming the Medicare rule transfers.
Frequently Asked Questions
How much does modifier 62 pay?
The fee schedule amount applicable to each co-surgeon is 62.5 percent of the global surgery fee schedule amount, subject to the lower of that or the billed amount. Actual dollar amounts vary by locality and year — check the current fee schedule.
How is modifier 66 paid?
By report. Team surgery has no fixed percentage. Where a Medicare fee already exists for a procedure billed with modifier 66, all physicians on the team must agree on the percentage each receives.
Do both surgeons have to append modifier 62?
Yes. If only one does, that physician is paid at 100 percent and the other’s claim denies. The two billing offices have to coordinate.
What is the difference between a co-surgeon and an assistant-at-surgery?
A co-surgeon performs a distinct part of the same procedure using the individual skills of their own specialty; the manual states that in a co-surgery the additional physician is not acting as an assistant. An assistant-at-surgery supports the primary surgeon. The payment reflects the difference: 62.5 percent each for co-surgeons, 16 percent for a physician assistant-at-surgery, and 13.6 percent of the physician amount for a PA, NP or CNS billing with modifier AS.
What if two surgeons operate through the same incision but perform different procedures?
Neither co-surgery nor multiple-surgery rules apply. Each surgeon bills their own procedure code. If one performs multiple procedures, the multiple-surgery rules apply to that surgeon only.
Why did my co-surgeon claim deny when the operative note clearly supports two surgeons?
Most often because the code’s co-surgery indicator is 0, in which case the payment adjustment rules do not apply, the first claim submitted is paid at 100 percent and later claims from other physicians are denied as medical necessity denials. Check Field 24 for the code and the year in question.
Can modifier 66 be used for two surgeons?
No. Modifier 66 applies to a team of more than two surgeons of different specialties. Contractor guidance identifies use for two or fewer surgeons as incorrect.
Related CASRAI Resources
- Modifiers 80, 81, 82 and AS — when an assistant is payable at all, and the three denial routes
- Modifier 51: multiple procedures — one surgeon, several procedures
- Modifier 58: staged or related procedure
- Modifier 78: the unplanned return to the operating room
- Modifier 79: unrelated procedure in the postoperative period
- Modifier 22: increased procedural services — the other by-report surgical claim
- Modifiers GX, GY and GZ against GA — who is liable when a surgical claim denies
- Modifiers 52 and 53: reduced versus discontinued
- Incident-to billing — the other place non-physician practitioner billing rules bite
- The False Claims Act in billing
Sources: CMS Medicare Claims Processing Manual, Publication 100-04, Chapter 12, Section 40.8 (claims for co-surgeons and team surgeons, Rev. 3721, effective 25 May 2017), Section 20.4.3 (assistant-at-surgery services), Section 110.2 (physician assistants) and Section 120.1 (nurse practitioners and clinical nurse specialists); Noridian Healthcare Solutions modifier 62 guidance (last updated 9 May 2025) and modifier 66 guidance (last updated 6 July 2026). Co-surgery, team surgery and assistant-at-surgery indicators are assigned per code in the annual Physician Fee Schedule and change each year. CPT is a registered trademark of the American Medical Association; modifier meanings are described here in summary and the AMA’s descriptor text is not reproduced. General reference material, not coding advice for a specific claim — verify against your own MAC’s current guidance and the payer’s policy.
