Locum tenens billing lets a practice keep collecting when its regular physician steps away, by submitting a substitute physician’s services under the regular provider’s National Provider Identifier (NPI) with a special modifier. Medicare calls the setup a fee-for-time compensation arrangement, and it hinges on two rules that trip up practices again and again: the Q6 modifier and a continuous 60-day limit. Follow both and a vacation, illness, or maternity leave never interrupts your revenue. Miss either and every affected claim becomes an overpayment you have to give back. This guide covers what locum tenens billing is, how the Q6 modifier works, how the 60-day clock actually counts, how Q5 differs, and the documentation that keeps an audit boring.
Key takeaways
- The Q6 modifier flags a service performed by a substitute physician under a fee-for-time (locum tenens) arrangement.
- Claims go out under the regular physician’s NPI, with Q6 appended to each substituted service.
- The 60-day limit runs continuously from the substitute’s first day and does not pause for weekends or off days.
- Q5 covers reciprocal billing between two physicians, while Q6 covers locum tenens.
- Written agreements and a running 60-day log are the difference between a clean claim and a refund.
What is locum tenens billing?
Locum tenens billing is the practice of submitting a temporary substitute physician’s claims under the absent regular physician’s name and NPI, rather than enrolling the substitute as a new provider. Medicare permits it when the regular physician is away for a real, temporary reason such as vacation, illness, continuing education, or parental leave.
The substitute is not a permanent hire. The practice pays them on a per diem or fee-for-time basis, which is exactly why Medicare renamed the arrangement a fee-for-time compensation arrangement. Because the claim carries the regular physician’s NPI while a different clinician does the work, understanding the split between the rendering provider and the billing provider is the foundation everything else sits on.
The Q6 modifier explained
The Q6 modifier identifies each service a substitute physician furnishes under a locum tenens arrangement. You append it to every line the substitute performed, on a claim that otherwise looks normal and carries the regular physician’s NPI.
Two limits matter. Q6 does not apply to an employed physician, since employees bill under their own credentials, and Q6 cannot be used for postoperative services delivered inside a global surgical period. If a surgery’s global package is already in play, the substitute’s follow-up visits fall under that package, not under Q6. Global periods are governed by their own set of surgical modifiers, including the surgical-care split marked by Modifier 54. Like any modifier, Q6 changes how a payer reads a line, the same way the CQ modifier reports who performed a therapy service.
How the 60-day rule works
A regular physician may bill a substitute’s work with Q6 only for a single continuous period of up to 60 days per absence. The details are where practices slip:
- The count starts on the substitute’s first day treating patients, not the day the regular physician left.
- It runs continuously. Weekends, holidays, and days the substitute sees no one all count.
- The clock resets only if the regular physician returns to work, even for a single day.
- On day 61, Q6 claims become an overpayment. The substitute must either stop or enroll in Medicare and bill under their own NPI.
The one common exception applies to a regular physician called to active duty in the armed forces, where the arrangement can extend beyond 60 days. Because exceeding the limit is the single costliest locum tenens error, set a calendar alert around day 45 so you can start independent enrollment before the clock runs out.
Q5 vs Q6: locum tenens vs reciprocal billing
Medicare offers two substitute-billing modifiers, and mixing them up creates denials. They describe different relationships.
| Modifier | Arrangement | Use it when |
|---|---|---|
| Q6 | Fee-for-time (locum tenens) | A substitute covers an absent regular physician and is paid per diem or fee-for-time. |
| Q5 | Reciprocal billing | Two physicians cover each other’s patients on an occasional, reciprocal basis. |
Pick the modifier that matches the actual agreement, not the one that feels close. Reciprocal coverage between colleagues is Q5. A paid temporary stand-in is Q6.
How to bill for a locum tenens physician
Once the arrangement qualifies, the workflow is simple and repeatable:
- Confirm the regular physician’s absence is temporary and the substitute is paid on a fee-for-time basis.
- Screen the substitute against the OIG exclusion and CMS preclusion lists before they see a patient.
- Submit claims under the regular physician’s name and NPI.
- Append the Q6 modifier to every service the substitute performed.
- Track the 60-day period from the substitute’s first service date.
- Confirm each non-Medicare payer’s own rules, since many do not follow the Q6 framework.
Sequencing matters when several modifiers land on one claim, a habit that also shows up with codes like Modifier 99.
Documentation and compliance requirements
Locum tenens claims live or die on paperwork. Keep a written agreement and an internal log that capture:
- The reason for the regular physician’s absence.
- The exact start and end dates the arrangement covers.
- The identities and NPIs of both the regular and substitute physicians.
- The compensation structure, confirming per diem or fee-for-time rather than employment.
- A running tally of the 60-day period, updated in real time rather than after the fact.
Retain these records for at least seven years so they are ready if a contractor asks. Well-organized documentation also keeps you aligned with broader compliance expectations for protected records.
Common locum tenens billing mistakes
The repeat offenders are easy to name and easy to prevent:
- Running past 60 continuous days without enrolling the substitute independently.
- Leaving off the Q6 modifier, or using it on an employed physician.
- Applying Q6 to postoperative care inside a global surgical period.
- Assuming commercial payers and Medicaid follow Medicare’s Q6 rules.
- Thin or informal documentation instead of a signed agreement and dated log.
A single owner for 60-day tracking and a standard onboarding checklist for every substitute clear most of these before a claim goes out.
Frequently asked questions
What is the Q6 modifier used for?
The Q6 modifier identifies a service performed by a substitute physician under a Medicare fee-for-time (locum tenens) arrangement. You append it to each substituted service on a claim billed under the regular physician’s NPI.
How is the 60-day locum tenens limit counted?
The 60 days run continuously from the substitute’s first date of service and include weekends, holidays, and non-service days. The period resets only if the regular physician returns to work, even for one day.
What is the difference between Q5 and Q6?
Q5 covers reciprocal billing, where two physicians cover each other’s patients on an occasional basis. Q6 covers locum tenens, where a paid substitute temporarily fills in for an absent regular physician.
Can locum tenens bill under their own NPI?
Not while working under a Q6 arrangement. Claims go out under the regular physician’s NPI. If coverage needs to continue past 60 days, the substitute must enroll in Medicare and bill under their own NPI.
The bottom line
Locum tenens billing keeps the lights on when a physician steps away, but only if you respect its two guardrails. Append the Q6 modifier to every substituted service, bill under the regular physician’s NPI, and watch the continuous 60-day clock like a hawk. Back it all with a signed agreement and a dated log, verify each payer’s own rules, and a temporary absence stops being a revenue gap. For the exact federal language, the CMS Medicare Claims Processing Manual, Chapter 1 spells out the fee-for-time compensation rules in full.
