Locum tenens billing: who bills, the Q6 modifier and the 60-day rule

What is locum tenens billing?

Every locum assignment produces two separate streams of billing, and people often mean different ones when they say “locum tenens billing”:

Payer billing

The practice, group or hospital bills Medicare, Medicaid or a commercial plan for the patient care the locum delivered. The question here is whose provider number goes on the claim, and for how long that's allowed.

Agency billing

The locum tenens agency invoices the facility for the clinician's days or hours, call, travel and other costs, at the contracted bill rate. This is the business side of locum tenens, and it happens regardless of how (or whether) the facility can bill payers for the work.

The two are linked by one practical risk. The facility owes the agency for every day worked, but it can only collect from payers if the locum's services are billable. A locum who isn't credentialed with a commercial plan, or who stays past Medicare's 60-day limit without enrolling, can generate a full agency invoice and very little collectable revenue.

A note on terms: “locum cover” is the usual phrase in the UK, Ireland, Australia and New Zealand, where general practice locums cover GP sessions in the same way. It means the same thing, temporary cover for an absent or vacant clinician, but the billing rules in those systems are different. This guide describes the U.S.

How Medicare locum tenens billing works: the Q6 modifier

Medicare now calls these fee-for-time compensation arrangements (they were formerly called locum tenens arrangements). They let a regular physician who is away bill for a substitute's services as if they were their own. The conditions are set out in the Medicare Claims Processing Manual, CMS Pub. 100-04, Chapter 1, §30.2.11:

1. The regular physician is unavailable to provide the services, for example because of illness, vacation, leave or continuing medical education.
2. The patient has arranged, or seeks, to receive services from the regular physician. The substitute is standing in for a specific physician's practice.
3. The substitute is paid on a per diem or similar fee-for-time basis by the regular physician or group, and is not an employee of the regular physician. In practice this is usually an independent contractor arrangement.
4. The substitute does not provide services for more than 60 continuous days (the 60-day rule, below).
5. Claims carry modifier Q6 on each service the substitute performed, billed under the regular physician's NPI.
6. The record identifies the substitute. The practice keeps a record of each service the substitute provided, associated with the substitute's NPI, and makes it available to the Medicare Administrative Contractor (MAC) on request.

When a physician leaves a group and the group brings in a locum to cover the vacancy while it recruits, the group can bill for the substitute under the departed physician's NPI with Q6, subject to the same 60-day limit.

Medicare rules change and MACs publish their own billing guidance. Check the current version of Pub. 100-04, Ch. 1, §30.2.11 and your MAC's instructions before relying on any summary, including this one.

What is the 60-day rule for locum tenens?

A substitute can be billed under the regular physician's NPI for a continuous period of no more than 60 days. The one statutory exception is a regular physician called to active military duty, where the substitute can be billed for longer.

Once the 60 days run out:

• The practice can no longer bill the substitute's services with Q6 under the absent physician's NPI.
• The substitute must be enrolled in Medicare and bill under their own NPI, typically with their payments reassigned to the group or facility they're working for.

Enrollment and reassignment take time, so the practical rule is to start the paperwork on day one of any coverage that might run long. Illustrative: a group's physician starts a three-month medical leave on March 1, and a locum covers the full period. The first 60 continuous days can be billed with Q6 under the absent physician's NPI. If the locum's own enrollment and reassignment aren't in place by the end of that window, the group keeps paying the agency for the remaining weeks with no clean way to bill Medicare for them.

How the 60 days are counted (for example, whether a gap restarts the clock, or how a group with several absent physicians should handle one locum) is exactly the kind of detail to confirm with your MAC rather than assume.

Locum tenens (Q6) vs reciprocal billing (Q5)

Medicare has a second, older substitute arrangement: reciprocal billing, where physicians informally cover for each other. It's easy to confuse with locum billing, and the modifier differs.

Both arrangements require the regular physician to be unavailable and both require the claim to identify the substitute's services. If an agency placed the clinician and the practice pays for their time, it's a fee-for-time arrangement and Q6 applies.

Locum tenens billing in hospitals, Medicaid and commercial plans

Hospitals. The facility bills its own facility charges as normal: a locum covering the emergency department or a hospitalist service doesn't change how the hospital bills for the room, nursing, imaging or the facility side of an ED visit. The professional services depend on who the absent clinician worked for. If the hospital employs the physician group, the hospital (or its billing entity) handles professional billing. If an outside group holds the contract, that group bills. Either way, every locum has to be credentialed and privileged by the hospital's medical staff office before they can see patients, which is usually the longest lead time in the whole process.

Commercial payers and Medicaid. These don't automatically follow Medicare's Q6 rules. Some commercial plans accept a Q6-style substitute arrangement for a limited period; many require the locum to be credentialed with the plan and bill under their own NPI from the first day; some sit in between. State Medicaid programs and Medicaid managed care plans set their own rules. Medicare Advantage plans follow their provider contracts. The only reliable approach is to check each payer contract and provider manual before the locum starts, and to track which payers each locum is credentialed with.

For facilities that run locums through a contingent labor program, the MSP often owns the agency side of this (orders, rates, invoices) while revenue cycle owns payer enrollment. See MSP vs VMS in healthcare staffing for who does what.

Locum tenens nurse practitioner billing

Medicare's Q6 provision is written for physicians. Recent legislation extended substitute billing to physical therapists in certain rural and underserved areas, but it doesn't cover nurse practitioners or physician assistants. In practice, a locum NP or PA generally bills under their own NPI, which means:

• The NP or PA must be enrolled in Medicare, with payments reassigned to the group or facility they're covering.
• Medicare pays most NP and PA services billed under their own NPI at a percentage of the physician fee schedule amount (85% for most services), not the full physician rate.
• Commercial and Medicaid enrollment has to be in place for each payer before the services are billable to that payer.
• State scope-of-practice and collaboration or supervision rules still apply on a short assignment.

The result is that credentialing lead time matters even more for APP locums than for physician locums: there is no 60-day bridge. A short NP assignment that starts before payer enrollment is complete may be clinically valuable and still largely unbillable. CMS guidance on substitute billing has been revisited several times, so check the current rules with your MAC before planning around them.

How locum tenens agencies bill facilities

Locum tenens physician staffing is billed to the facility at a contracted bill rate, which covers the clinician's pay, malpractice insurance, licensing and credentialing, travel and the agency's margin (the full spread is covered in bill rate vs pay rate). The common billing units are:

• Daily or shift rate for a defined day (for example, 10 hours), with hourly overtime beyond it.
• Hourly rate, common for emergency medicine, anesthesia and APP coverage.
• Call pay: a flat rate per call period, plus an hourly rate for call-back time actually worked.
• Travel and lodging, either included in the bill rate or passed through at cost, sometimes with an admin fee.
• Malpractice, almost always built into the rate rather than invoiced separately.

Illustrative invoice for one week-plus of physician coverage. Every rate below is an assumption chosen to show the structure, not market data for any specialty.

Read a locum contract for the details that move the total: how a “day” is defined, when overtime starts, whether call-back hours are billed in full-hour increments, whether travel is capped, and what the cancellation terms are. Health systems that use several agencies usually standardize these terms on a rate card; see how hospitals build staffing rate cards. Physicians weighing the other side of the arrangement can see locum tenens 1099 vs W-2 for taxes, entities and insurance.

What does short-notice locum tenens coverage cost?

Short-notice coverage costs more for structural reasons, not just because the facility is in a hurry:

• A smaller pool. Only clinicians who are already licensed in the state and available on the needed dates can start quickly.
• Expedited credentialing. Privileging still has to happen; doing it in days rather than weeks takes extra work on both sides. Some hospitals use temporary privileges for urgent patient care needs, within their bylaws.
• Premiums. Contracts often add a rush premium, either a percentage of the bill rate or a flat daily amount, for assignments that start inside a set notice window, plus holiday rates.
• Fixed costs over fewer days. Credentialing, licensing and travel booked at the last minute are spread over a short assignment.

Illustrative: a 15% rush premium on the $2,600 day above adds $390 a day, or $3,900 over ten clinical days, before last-minute airfare. The usual alternative, leaving the schedule uncovered, means diverted patients, closed clinic sessions and burnout for the remaining team, so the comparison is premium versus lost revenue, not premium versus zero.

The best defense is knowing the market before you're in a hurry. Facilities that benchmark locum and contract rates by role and region can tell a fair rush quote from an outlier. That is what ClinicalRate for hospitals and facilities is built for: live pay and bill rates for 400+ clinical roles, by state and metro, refreshed every business day.

Frequently asked questions