Modifier Q6: billing while a locum holds your panel

How do I bill for a locum tenens covering my practice?

Bill it under your own NPI as if you personally provided the service, and add modifier Q6 to the code. Medicare calls this a fee-for-time compensation arrangement — the modern name for what most billers still call locum tenens — and the payment goes through your own enrollment and your own numbers, not the substitute's 1Ref 1Centers for Medicare & Medicaid Services (2026).Internet-Only Manuals (IOMs).That CMS program instructions live in the public Internet-Only Manuals, including the Medicare Claims Processing Manual, which is the operative source defining fee-for-time compensation (Q6) and reciprocal (Q5) billing arrangements, their continuous-coverage window, and documentation requirements.. This is squarely a medicare-billing mechanism, built for exactly the situation of a solo practice with no one else to bill under while you're out.

What modifier Q6 actually signals

Q6 tells the payer that the physician of record did not personally perform the service — a temporary substitute did, under a fee-for-time arrangement — while the claim itself is otherwise submitted exactly as if you had. The substitute's own NPI does not appear on the claim; your NPI carries both the rendering and billing role, the same as any claim you'd bill yourself. That's the entire mechanical difference between an ordinary claim and a Q6 claim: one modifier, added to a claim that otherwise looks like your own work.

The related modifier Q5 covers a reciprocal arrangement instead — two physicians who informally cover for each other without a per-diem or per-service payment changing hands, common in small or rural practices that trade coverage back and forth. Q6 is for a paid, arranged substitute; Q5 is for an unpaid reciprocal swap. Both share the same underlying idea: the claim bills under the absent physician's own identity, and a modifier discloses that someone else rendered it.

Why this exists, and what it is not

The point of a fee-for-time arrangement is continuity — a solo practice can keep billing normally during a planned or unplanned absence instead of losing revenue or credentialing a temporary clinician with every payer on short notice. It is not incident-to billing, where a supervised clinician works in your own office under your direct oversight; a Q6 substitute is covering your entire absence, often without your presence at all, which is materially different even though both end up billed under your NPI. It also isn't a question of credential-level modifiers — Q6 does not downgrade payment the way a supervision modifier can, because the claim bills exactly as if you performed the service personally. And whether the mechanism is available to you at all depends on your own participation, non-par, opt-out status: it assumes you are enrolled and billing Medicare directly, so it doesn't apply if you've opted out of the program entirely.

The coverage window, documentation, and where the specifics live

Medicare limits how long a fee-for-time arrangement can run and requires you to be able to identify the substitute for any given date of service if asked, but the exact continuous-coverage window and documentation format are set out in the Medicare Claims Processing Manual, which is the source to check rather than a remembered number 1Ref 1Centers for Medicare & Medicaid Services (2026).Internet-Only Manuals (IOMs).That CMS program instructions live in the public Internet-Only Manuals, including the Medicare Claims Processing Manual, which is the operative source defining fee-for-time compensation (Q6) and reciprocal (Q5) billing arrangements, their continuous-coverage window, and documentation requirements.. Because that manual is updated periodically, confirm the current limit before assuming a duration you learned even a year or two ago still holds.

Keep your own internal log regardless of what the manual currently specifies: the substitute's name, NPI, and the dates and codes they covered for you. Nothing about that log goes on the claim itself, but a payer or an auditor can ask you to produce it, and the arrangement only works if you can answer that question immediately rather than reconstruct it after the fact.

MAC guidance and jurisdiction-specific documentation

Because Medicare claims administration is regionalized, your own Medicare Administrative Contractor may publish its own documentation and signature expectations for reciprocal and fee-for-time billing on top of the national manual, and CMS publishes which MAC serves your jurisdiction 2Ref 2Centers for Medicare & Medicaid Services (2026).Medicare Administrative Contractors.That Medicare claims administration is regionalized across MACs and CMS publishes which MAC serves each jurisdiction, so a solo can find the contractor that may add its own documentation expectations for reciprocal and fee-for-time billing.. CGS Medicare, for one, publishes its own billing articles covering exactly this kind of jurisdiction-specific guidance, and it's a useful model for what to expect from whichever MAC actually processes your claims — read your own MAC's published article rather than assume every jurisdiction handles the paperwork identically 3Ref 3CGS Medicare (2026).CGS Medicare.Cited as one example of a Medicare Administrative Contractor's own published billing articles and documentation guidance, illustrating the kind of jurisdiction-specific instruction a reader should confirm with their own MAC rather than assume is universal..

How the claim actually pays

Because a Q6 claim bills under your own enrollment, it pays at your own rate — the same Medicare Physician Fee Schedule amount you'd receive had you performed the service yourself, since the fee schedule sets payment by the billing clinician's own numbers, not the identity of whoever actually rendered the care 4Ref 4Centers for Medicare & Medicaid Services (2026).Physician Fee Schedule.That the Medicare Physician Fee Schedule sets payment for clinician services by the billing clinician's own enrollment, which is why a Q6 claim billed under the regular physician's NPI pays at that physician's normal rate rather than a reduced locum rate.. There is no separate, lower locum rate. That also means the modifier is invisible to your revenue, provided it's used correctly and documented — the only real risk is compliance, not payment accuracy.

The convention is Medicare-specific, and it does not automatically carry over to commercial payers or to medicaid-billing arrangements: many commercial plans do not recognize the reciprocal-billing modifiers at all and instead require a covering clinician to be independently credentialed and billed under their own NPI, whatever your Medicare arrangement looks like. Confirm each commercial payer's own policy before assuming Q6 travels with the claim to every plan a patient carries.

A short setup for using it correctly

Set this up before the absence starts, not during it, since the documentation trail is what makes a Q6 claim defensible.

• Confirm with your MAC, and separately with each commercial payer, whether it recognizes reciprocal or fee-for-time billing at all, and under what terms.
• Log the substitute's name, NPI, and covered dates internally — never on the claim.
• Bill every covered service under your own NPI in both the rendering and billing fields, with Q6 appended.
• Confirm the current continuous-coverage window and documentation format in the Medicare Claims Processing Manual before an absence runs long.
• Even a preventive-services visit — a Welcome to Medicare exam a substitute performs during your absence — follows the identical Q6 rule; the modifier doesn't depend on the type of visit.

Q6 also sits in a different modifier family than the NCCI-related pairs like 59, xe, xs, xu, which unbundle code pairs rather than identify who rendered a service, and it works independently of beneficiary-liability modifiers like ga, gz, gy, which flag who pays, not who performed the visit.