Modifier Q6 is a HCPCS Level II modifier used to identify services furnished by a locum tenens (substitute) physician under Medicare.

A locum tenens arrangement allows a temporary substitute physician to treat patients on behalf of a regular physician who is temporarily unavailable due to vacation, illness, maternity leave, military service, continuing medical education, or other temporary absences.

Instead of billing under the substitute physician’s Medicare enrollment, Medicare allows the regular physician to submit the claim using their own NPI, provided all CMS requirements are satisfied and Modifier Q6 is appended to the procedure code.

Modifier

Modifier Name

Service Furnished by a Locum Tenens Physician

(Current HCPCS descriptor: Service furnished under a fee-for-time compensation arrangement by a substitute physician, or by a substitute physical therapist furnishing outpatient physical therapy services in a health professional shortage area, a medically underserved area, or a rural area.)

Plain English Explanation

Modifier Q6 tells Medicare:

“A temporary substitute physician provided this service while the patient’s regular physician was temporarily unavailable.”

Although another physician actually treated the patient, Medicare pays the claim under the regular physician’s billing number, provided all Medicare requirements are met.

Purpose

Modifier Q6 is used to:

Identify locum tenens services.
Allow temporary physician coverage.
Prevent interruption of patient care.
Allow payment under the regular physician’s Medicare enrollment.
Comply with Medicare substitute physician billing rules.

Understanding Modifier Q6

A locum tenens physician is:

A temporary substitute.
Usually an independent contractor (not an employee in the locum arrangement).
Paid on a per diem or similar fee-for-time basis.
Covering the practice only temporarily.

The patient generally believes they are receiving care from their usual physician’s practice while the regular physician is absent.

When to Use Modifier Q6

Append Modifier Q6 when all Medicare conditions are met:

The regular physician is temporarily unavailable.
The patient sought treatment from the regular physician or practice.
The substitute physician is paid on a fee-for-time (for example, daily or hourly) basis.
The substitute physician provides services for no more than 60 continuous days for the same absent physician.
The claim is submitted under the regular physician’s NPI with Modifier Q6.

Common CPT codes include:

CPT Code	Description
99202–99205	New patient office visits
99211–99215	Established patient office visits
99381–99397	Preventive medicine visits
99441–99443 (when payer applicable)	Telephone E/M services
Other covered Medicare physician visit services	When substitute billing requirements are met

When NOT to Use Modifier Q6

Do not use Modifier Q6 when:

The substitute physician is permanently replacing the physician.
Coverage exceeds 60 continuous days (unless a specific statutory exception applies).
The substitute physician is independently billing Medicare for the services.
The physician is simply adding staff rather than replacing an absent physician.
The payer does not recognize Medicare substitute physician rules.

Medicare Rules

Medicare requires all of the following:

The regular physician must be temporarily unavailable.
The patient must seek services from the regular physician.
The substitute physician must be compensated on a fee-for-time basis.
The substitute physician generally may not furnish Medicare services for more than 60 continuous days for the same absent physician.
The claim is submitted under the regular physician’s NPI with Modifier Q6.
The practice must maintain records identifying the substitute physician and the dates services were provided for audit purposes.

Commercial Insurance Rules

Commercial payer policies vary.

Some commercial insurers:

Follow Medicare locum tenens rules.
Require credentialing of the substitute physician.
Do not recognize Modifier Q6.
Require different substitute physician billing procedures.

Always verify payer-specific billing requirements.

Documentation Requirements

Documentation should include:

Reason for the regular physician’s absence.
Name of the substitute physician.
Dates of substitution.
Medical record identifying the actual rendering physician.
Fee-for-time compensation arrangement.
Evidence that the 60-day limit was not exceeded.
Regular physician’s NPI on the claim.
Complete clinical documentation.

Real Billing Examples

Example 1 – Vacation Coverage

Dr. Smith is on a two-week vacation.

Dr. Jones provides office visits for Dr. Smith’s Medicare patients.

Billing

CPT 99213-Q6
Claim submitted under Dr. Smith’s NPI

Example 2 – Medical Leave

A physician takes six weeks of medical leave.

A locum tenens physician covers the practice.

Billing

CPT 99214-Q6
Regular physician’s NPI

Example 3 – Maternity Leave

A substitute physician provides patient care during maternity leave.

Coverage lasts 45 days.

Billing

Appropriate CPT code
Modifier Q6

Example 4 – Rural Physical Therapy

An eligible substitute physical therapist furnishes outpatient therapy services in a qualifying rural area under CMS substitute therapist rules.

Billing

Appropriate therapy CPT code
Modifier Q6 (when all CMS requirements are satisfied).

Example 5 – Incorrect Billing

A substitute physician provides services for 90 continuous days, and the practice continues billing with Modifier Q6.

This is generally incorrect, because the continuous substitution exceeds Medicare’s standard 60-day limit.

CMS-1500 Claim Example

Field	Example
CPT	99213
Modifier	Q6
Billing NPI	Regular physician’s NPI
Rendering Documentation	Substitute physician identified in practice records
Units	1

Common Denials

Missing Modifier Q6.
Coverage exceeds the 60-day limit.
Substitute physician improperly enrolled or billed.
Incorrect billing NPI.
Missing substitute physician records.
Payer does not recognize locum tenens billing.

Correcting Denials

Verify all Medicare locum tenens requirements.
Confirm the 60-day continuous service limit was not exceeded.
Verify billing under the correct physician’s NPI.
Maintain records identifying the substitute physician.
Submit a corrected claim.
Appeal with supporting documentation if appropriate.

Coding Tips

Modifier Q6 is only for temporary substitute physician arrangements meeting CMS requirements.
The regular physician’s NPI remains on the claim.
Maintain detailed logs of substitute physician dates.
Monitor the 60-day continuous service limit carefully.
Review payer-specific substitute physician policies before billing.

Modifier Q6 vs Modifier Q5

Modifier	Description
Q6	Fee-for-time substitute (locum tenens) physician arrangement
Q5	Reciprocal billing arrangement between physicians

Modifier Q6 vs Modifier GC

Modifier	Description
Q6	Temporary substitute physician
GC	Resident service under teaching physician supervision

Modifier Q6 vs Modifier 95

Modifier	Description
Q6	Temporary substitute physician billing
95	Telehealth audio-video service

Frequently Asked Questions (FAQs)

Q1. What does Modifier Q6 mean?

Answer: It identifies services furnished by a temporary locum tenens (substitute) physician under a Medicare fee-for-time compensation arrangement.

Q2. Who submits the Medicare claim?

Answer: The regular physician submits the claim using their own NPI, with Modifier Q6 appended to the procedure code.

Q3. What is the Medicare 60-day rule?

Answer: A substitute physician generally may not furnish Medicare services for the same absent physician for more than 60 continuous days, unless a specific statutory exception applies.

Q4. Does the substitute physician need to be identified?

Answer: Yes. Although the claim is billed under the regular physician’s NPI, the practice must maintain records identifying the substitute physician and make them available upon Medicare request.

Q5. Can commercial insurance use Modifier Q6?

Answer: Some commercial payers recognize Q6, while others require the substitute physician to be credentialed separately. Always verify payer policy.

AR Caller Tips

When following up on Q6 claims:

Verify the claim was billed under the correct physician’s NPI.
Confirm Modifier Q6 was appended.
Check whether the substitute period exceeded 60 continuous days.
Verify payer recognition of locum tenens billing.
Document payer representative names, reference numbers, and appeal instructions.

Interview Questions

Question 1

What is Modifier Q6 used for?

Answer: Billing services furnished by a temporary locum tenens physician under Medicare.

Question 2

Who receives Medicare payment?

Answer: The regular physician bills and receives payment, provided all CMS requirements are met.

Question 3

What is the 60-day rule?

Answer: The substitute physician generally cannot provide Medicare-covered services for the same absent physician for more than 60 continuous days.

Question 4

Who is listed on the CMS-1500 claim?

Answer: The claim is submitted under the regular physician’s NPI, with Modifier Q6 appended to the applicable procedure code.

Practice Scenario

Scenario

Dr. Williams takes a four-week vacation. Dr. Patel, an independent locum tenens physician, sees Medicare patients during Dr. Williams’ absence and is paid on a daily basis.

Question

How should the claims be billed?

Answer

Report:

Appropriate CPT code (for example, 99213)
Modifier Q6
Bill under Dr. Williams’ NPI

Maintain documentation identifying Dr. Patel as the substitute physician and ensure the coverage does not exceed the Medicare 60-day continuous service limit.

Related Medicare Special Modifiers

Q5 – Service Furnished Under a Reciprocal Billing Arrangement
GC – Service Performed by a Resident Under Teaching Physician Direction
GE – Service Performed by a Resident Without Presence of a Teaching Physician (Primary Care Exception)
QW – CLIA Waived Test

Common Billing Mistakes

Billing beyond the 60-day limit.
Using the substitute physician’s NPI instead of the regular physician’s NPI.
Forgetting Modifier Q6.
Missing substitute physician documentation.
Using Q6 for permanent physician replacements.
Assuming all commercial payers follow Medicare locum tenens rules.

Key Takeaways

Modifier Q6 identifies services furnished by a temporary locum tenens physician.
Medicare requires a fee-for-time compensation arrangement.
Claims are billed under the regular physician’s NPI.
The substitute physician generally may not provide services for more than 60 continuous days for the same absent physician.
Complete documentation is essential for Medicare compliance and audit readiness.

References

CMS Medicare Claims Processing Manual, Pub. 100-04, Chapter 1, Section 30.2.11 – Locum Tenens (Substitute Physician) Arrangements.
CMS Transmittal R1335CP – Substitute Physician (Locum Tenens) Billing.
CGS Medicare – Services Provided Under Locum Tenens Provisions.
HCPCS Level II Code Book.
CPT® Professional Edition (American Medical Association).

Conclusion

Modifier Q6 is a specialized Medicare modifier that supports temporary substitute physician (locum tenens) billing while maintaining continuity of patient care. Proper use requires strict compliance with Medicare’s substitute physician rules, including billing under the regular physician’s NPI, maintaining detailed documentation, compensating the substitute on a fee-for-time basis, and observing the 60-day continuous service limitation. Accurate reporting of Modifier Q6 helps practices remain compliant, avoid denials, and ensure appropriate reimbursement during temporary physician absences.

Educational Disclaimer

This article was prepared with the assistance of artificial intelligence (AI) for educational and informational purposes. It is based on publicly available CMS guidance, Medicare Claims Processing Manual provisions, HCPCS Level II guidance, and general medical billing principles. It is not an official publication of CMS or the American Medical Association (AMA). Always consult the latest CMS Medicare Claims Processing Manual, HCPCS Level II Code Book, CPT® Professional Edition, Medicare Administrative Contractor (MAC) guidance, and payer-specific billing policies before coding, billing, or submitting claims.