Locum Tenens Billing Guidelines - Medicare Rules, Q6 Modifier and 60-Day Rule

When a physician is temporarily unavailable, practices often engage a substitute so patients continue to receive care. Under Medicare Part B, this arrangement is governed by the payment rules for fee-for-time compensation arrangements. 

The Medicare Claims Processing Manual (Pub. 100-04, Chapter 1, §30.2.11) titles the section “Payment Under Fee-For-Time Compensation Arrangements (formerly referred to as Locum Tenens Arrangements).”

These rules determine whether the regular physician or medical group may submit the claim and receive payment for the substitute’s services, when modifier Q6 is required, whose NPI appears in the applicable claim field, and how long the arrangement may continue.

 The rules apply only to Medicare fee-for-service claims processed by A/B Medicare Administrative Contractors. Medicaid, Medicare Advantage, and commercial payers set their own requirements, and practices that need help sorting out payer specific variation often lean on a partner that handles medical billing consulting across multiple payer types.

What Is Locum Tenens Billing?

In everyday practice language, “locum tenens” describes a temporary substitute physician who covers for a regular physician during an absence such as illness, pregnancy, vacation, or continuing medical education. The substitute is typically paid on a per diem or similar fee-for-time basis and works as an independent contractor rather than an employee.

Medicare’s official term for the arrangement is fee-for-time compensation. CMS moved away from using “locum tenens” exclusively after the 21st Century Cures Act broadened that phrase to cover both fee-for-time compensation and reciprocal billing. The manual language remains the authoritative reference point: fee-for-time compensation arrangements, formerly referred to as locum tenens arrangements.

The arrangement is meant for temporary substitution only. It is not a way to cover permanent vacancies or long-term staffing gaps. Practices expecting ongoing coverage needs should look at proper physician credentialing instead of stretching a temporary billing exception past its intended use.

Medicare’s Fee-for-Time Requirements

Under §30.2.11, a patient’s regular physician or physical therapist may bill for a substitute’s covered visit services, and receive payment on assignment, when all of the following are true.

• The regular physician or physical therapist is unavailable.
• The Medicare beneficiary has arranged or seeks to receive services from the regular physician or physical therapist.
• The regular physician or physical therapist pays the substitute on a per diem or similar fee-for-time basis.
• The substitute does not treat Medicare patients for a continuous period longer than 60 days, subject to the active duty exception.
• The claim carries HCPCS modifier Q6 after the procedure code.

A “regular physician” is whoever is normally scheduled to see the patient, including specialists. The rule applies to physicians only. Non-physician practitioners such as nurse practitioners, physician assistants, and CRNAs generally cannot be billed under fee-for-time or reciprocal arrangements. 

One exception exists for Medicare-enrolled physical therapists furnishing outpatient physical therapy in a Health Professional Shortage Area, Medically Underserved Area, or rural area, effective since June 13, 2017.

Three arrangements fall under the same core rules.

• Individual physician: claims are submitted under the regular physician’s own billing identity.
• Medical group: the group may bill on behalf of a group physician, provided the substitute has not reassigned payment rights through a CMS-855R and the other §30.2.11 conditions are met.
• Departed physician: a physician who has left the group may still be treated as the “regular physician” for up to 60 days while a temporary replacement covers their patients.

The Continuous 60-Day Period

CMS caps the arrangement at a continuous period of 60 days, with an active duty exception. MAC guidance defines that period as starting on the first day the substitute sees Medicare Part B patients of the regular physician, and ending on the last day before the regular physician returns. The period stays continuous even if there are gaps without covered services, or if a second substitute steps in during the window.

Active duty exception. A physician or physical therapist called to active duty as a reservist may bill under a fee-for-time arrangement beyond 60 days if every other requirement is still met.

Once the continuous period ends, the fee-for-time exception no longer covers billing the substitute’s services under the regular physician’s identity. Anything after that point needs its own valid Medicare enrollment and billing arrangement. If a physician has left the group, the practice can bill a temporary replacement under the departed physician’s NPI for up to 60 days, but it cannot extend that window by rotating in a new substitute.

The Q6 Modifier

Modifier Q6 identifies a service furnished under a fee-for-time compensation arrangement by a substitute physician, or by a substitute physical therapist furnishing outpatient physical therapy in a shortage, underserved, or rural area.

On Form CMS-1500, Q6 goes in item 24D, after the procedure code, or the electronic equivalent. Using the modifier certifies that the substitute’s services are documented in the regular physician’s or group’s records, available for inspection, medically necessary, and eligible to be billed under this arrangement.

Q6 applies only to fee-for-time arrangements. Reciprocal billing uses Q5 instead, under a separate manual section, §30.2.10. Confusing the two produces an incorrect claim. For a closer look at how modifiers are placed and validated on a claim, iRCM’s modifier reference guides walk through the same field-level logic.

Global surgical packages raise separate issues, so confirm current MAC handling for any post-operative services inside a global period.

Whose NPI Goes Where

CMS treats three identifiers as distinct, and they should never be swapped.

In short: the claim identifies the physician being substituted for, and the practice separately maintains a service-level record tying each visit to the substitute’s NPI.

Compensation Structure

CMS requires the regular physician, physical therapist, or group to pay the substitute on a per diem or similar fee-for-time basis. An arrangement without that structure does not qualify for the exception.

Does the Substitute Need to Be Enrolled?

The manual does not require the substitute to be enrolled in Medicare as a condition of the billing exception itself. Several MACs confirm that a fee-for-time substitute does not need Medicare enrollment to have their services billed this way, as long as they hold a valid NPI and an unrestricted license in the state where they practice.

That said, enrollment status is separate from ordinary compliance work. Practices should still verify licensure, run exclusion and preclusion screening, and meet internal credentialing requirements before the substitute sees patients. Because credentialing can take longer than expected, many groups start locum tenens credentialing well before the substitute’s first day.

If the arrangement is expected to run past 60 days, or the physician is joining the group longer term, subsequent services need a proper Medicare enrollment and reassignment, through full credentialing services rather than the temporary exception.

Fee-for-Time vs. Reciprocal Billing

Submitting the Claim (CMS-1500 / 837P)

• Procedure code with modifier Q6 in item 24D, or the electronic equivalent.
• On group claims, the NPI of the physician being substituted for in item 24J.
• Standard billing provider information for the regular physician or group.
• Normal place of service, diagnosis, and medical necessity requirements still apply.
• Payment and limiting charge are calculated as if the regular physician performed the service.

See iRCM’s breakdown of professional versus institutional claim formats for more on how CMS-1500 and 837P claims differ from institutional billing.

Medicaid and Commercial Payers

Medicare’s fee-for-time rules do not automatically apply to Medicaid, Medicare Advantage, or commercial insurance. Some commercial payers accept a Q6-style approach. Others require the substitute to be credentialed and enrolled under their own NPI from day one, or apply different time limits and documentation rules entirely.

Before billing a non-Medicare claim, review the specific payer contract and provider manual, confirm the required identifiers and any temporary-provider modifier, and document the payer’s written policy. A structured revenue cycle management process makes this kind of payer verification routine rather than a scramble after a denial.

Documentation to Keep on File

For Medicare fee-for-time claims, retain:

• A service-level record naming the substitute and their NPI, available to the MAC on request.
• Evidence the compensation is per diem or similar fee-for-time.
• A log tracking the continuous period, from first Medicare service date to the projected 60-day cutoff.

Good practice also means keeping the written engagement agreement, license verification, exclusion screening results, and the underlying medical records.

Where Practices Go Wrong

• Appending Q6 when the compensation is not actually per diem or fee-for-time.
• Using Q6 for non-physician practitioners outside the physical therapist exception.
• Losing track of the continuous period from the first service date.
• Continuing to bill under the exception after the 60 days have passed.
• Reporting the substitute’s NPI as the rendering provider, instead of the physician being substituted for.
• Mixing up Q5 and Q6.
• Assuming commercial or Medicaid payers follow Medicare rules without checking.
• Using the arrangement to cover a permanent vacancy past the temporary window.

A practice with denial management already in place tends to catch a mismatched Q6 claim before it turns into lost revenue, not after.