⚕️ Outpatient Therapy Modifiers Reference Guide (CMS / Medicare Part B)

Executive Summary & Regulatory Authority

Governing Regulations: CMS Internet-Only Manual (IOM) Pub. 100-04 (Medicare Claims Processing Manual), Chapter 5, §20; Pub. 100-02 (Medicare Benefit Policy Manual), Chapter 15, §§220–230; 42 CFR §414.64. Mandatory Scope: Therapy modifiers are required on all outpatient therapy claims billed to Medicare Part B and commercial payers following CMS policy, regardless of provider setting (private practice, outpatient hospital, CORF, SNF Part B, HHA Part B, or physician clinic).

1. Primary Discipline Modifiers (Plan of Care Identifiers)

Therapy discipline modifiers are mandatory Level II HCPCS modifiers that indicate services were rendered under an established, certified outpatient therapy plan of care. They are mutually exclusive for the same service line.

Modifier	Plan of Care Discipline	Qualified Billing Practitioners	CMS Claims Processing Manual Rule
-GP	Physical Therapy (PT)	Physical Therapist (PT), Physical Therapist Assistant (PTA under supervision), Physician / NPP furnishing PT	Required on all PT services (evaluations, re-evaluations, timed/untimed modalities, and procedures)
-GO	Occupational Therapy (OT)	Occupational Therapist (OT), Occupational Therapy Assistant (OTA under supervision), Physician / NPP furnishing OT	Required on all OT services (evaluations, re-evaluations, ADL training, cognitive, and therapeutic modalities)
-GN	Speech-Language Pathology (SLP)	Speech-Language Pathologist (SLP), Physician / NPP furnishing speech therapy	Required on all SLP speech, swallowing, cognitive, and voice evaluation and treatment services

Scope of Mandate (Where Modifiers Are Required)

Discipline modifiers are not restricted to physician or incident-to billing; they are required on all professional and institutional claims:

Professional Claims (CMS-1500 / 837P): Private practices, physician/NPP clinics (POS 11), home visits (POS 12), telehealth (POS 02/10).
Institutional Outpatient Claims (UB-04 / 837I):
- Hospital Outpatient Departments (HOPD) — Type of Bill (TOB) 13X
- Skilled Nursing Facilities (SNF Part B long-term residents) — TOB 22X, 23X
- Comprehensive Outpatient Rehabilitation Facilities (CORFs) — TOB 75X
- Outpatient Rehabilitation Facilities / Rehabilitation Agencies (ORFs) — TOB 74X
- Home Health Agencies billing Part B outpatient therapy — TOB 34X

2. Assistant Payment Reduction Modifiers (-CQ & -CO)

Under Section 53107 of the Bipartisan Budget Act of 2018 and 42 CFR §414.64, services furnished in whole or in part by a therapy assistant are reimbursed at 85% of the Medicare Physician Fee Schedule (MPFS).

Modifier	Assistant Discipline	Required Companion Modifier	Payment Differential
-CQ	Physical Therapist Assistant (PTA)	Appended alongside -GP	Paid at 85% of MPFS allowable
-CO	Occupational Therapy Assistant (OTA)	Appended alongside -GO	Paid at 85% of MPFS allowable

The CMS 10% De Minimis Standard

De Minimis Standard: The assistant modifier (-CQ or -CO) is triggered whenever a PTA or OTA furnishes more than 10% of a service independently of the supervising therapist.
Timed 15-Minute Units: 10% of a 15-minute unit equals 1.5 minutes. In practice, if a PTA/OTA provides 2 or more minutes of a 15-minute unit without the therapist actively participating, the unit must be billed with -CQ or -CO.
Untimed Codes (e.g., 97150 Group Therapy, Unlisted): If the assistant furnishes >10% of the total session time independently, append the assistant modifier.
Full Service by Assistant: If the assistant provides the entire service independently under general supervision, the assistant modifier is mandatory for all units.
Students: Services provided by therapy students are not billable under Medicare Part B unless the licensed clinician is physically present in the room actively directing and participating throughout the entire service. Modifiers -CQ and -CO apply only to licensed/certified PTAs and OTAs, never to students.

3. CY 2026 Therapy Thresholds & Modifier -KX

Section 50202 of the Bipartisan Budget Act of 2018 permanently repealed the former Medicare “therapy cap” and established an annual statutory threshold system linked to the Medicare Economic Index (MEI).

CY 2026 Medicare Part B Threshold Amounts

Threshold Category	2026 Amount	Statutory Rule & Billing Requirement
PT & SLP Combined Threshold	$2,480	Once incurred Part B expenses exceed $2,480, -KX must be appended to all subsequent PT and SLP claims to attest to continued medical necessity.
OT Separate Threshold	$2,480	Monitored on an independent financial track; -KX must be appended once incurred OT expenses exceed $2,480.
Targeted Medical Review (MR) Threshold	$3,000	Fixed at ** $3, 000 t h r o ug h C Y 2028 * * . C l aim se x cee d in g$ 3,000 do not face automatic denial, but are subject to targeted review by Supplemental Medical Review Contractors (SMRC) or MACs.

Attestation Function of Modifier -KX

Appending -KX is a binding legal attestation that:
1. The patient requires continuing, complex, skilled therapy services beyond the financial threshold.
2. The medical record contains explicit, objective documentation supporting medical necessity and justification for exceeding the cap.
Automatic Claim Denial: Claims submitted above $2,480 in cumulative allowable expenses without -KX are automatically denied by Medicare adjudication systems (Remittance Advice Remark Code MA01 / Claim Adjustment Reason Code 119).

4. Beneficiary Financial Liability Modifiers (ABN Rules)

When therapy services fail to meet Medicare coverage criteria or medical necessity guidelines, the provider must issue a valid Advance Beneficiary Notice of Noncoverage (Form CMS-R-131) prior to delivering care:

Modifier	Regulatory Meaning	Impact on Claim & Liability
-GA	Waiver of Liability / ABN on File	Provider obtained a signed, valid ABN prior to treatment because service is expected to deny as not medically necessary (e.g., non-skilled maintenance). Medicare denies claim; patient is legally liable.
-GX	Notice of Voluntary ABN Issued	ABN issued voluntarily for services that are statutorily excluded from Medicare benefits.
-GY	Statutory Exclusion	Service is statutorily non-covered by Medicare (not a covered benefit under Title XVIII). Claim denies; patient is liable even without an ABN.
-GZ	No ABN on File (Expected Denial)	Service expected to deny as not medically necessary, but no ABN was obtained. Claim is denied, and provider cannot balance-bill the patient (provider writes off balance).

5. CMS “Always Therapy” vs. “Sometimes Therapy” Codes

CMS categorizes physical medicine and rehabilitation codes to govern modifier requirements (CMS IOM Pub. 100-04, Ch. 5, §20.1):

“Always Therapy” Codes

Must always have a therapy discipline modifier (-GP, -GO, or -GN) appended on every claim line, regardless of whether furnished by a therapist, physician, or NPP.
Subject to the 8-Minute Rule (timed units) and the therapy financial threshold.
Common Examples:
- Evaluations / Re-evaluations: 97161, 97162, 97163, 97164 (PT); 97165, 97166, 97167, 97168 (OT)
- Timed Procedures: 97110 (Therapeutic Exercise), 97112 (Neuromuscular Re-education), 97116 (Gait Training), 97140 (Manual Therapy), 97530 (Therapeutic Activities), 97535 (Self-Care / ADL)
- Speech Services: 92507 (Speech/Language Treatment), 92526 (Swallowing Therapy), 97129 / 97130 (Cognitive Intervention)

“Sometimes Therapy” Codes

Codes that are physical medicine procedures but can be provided either under a certified therapy plan of care or outside of one (e.g., by a physician acting as a physician).
If furnished under a therapy plan of care: Must be appended with -GP, -GO, or -GN.
If furnished outside a therapy plan of care by a physician: Billed without a therapy discipline modifier (not counted against the therapy threshold).
Common Examples:
- Active wound care management: 97597, 97598, 97602
- Orthotic / prosthetic management: 97760, 97761, 97763
- Strapping / casting: 29105, 29125, 29540

6. Modifier Sequencing & Multi-Modifier Positioning

CMS-1500 (Item 24D) and electronic 837P/837I transactions allow up to four modifiers per line item. Sequence therapy modifiers logically to avoid processing errors:

Claim Line Multi-Modifier Sequencing Structure:
[CPT/HCPCS Code] ➔ [Position 1: Primary Discipline (-GP/-GO/-GN)]
                 ➔ [Position 2: Assistant Differential (-CQ/-CO, if PTA/OTA >10%)]
                 ➔ [Position 3: Threshold Attestation (-KX, if >$2,480)]
                 ➔ [Position 4: NCCI Distinct Service (-59/-XS) or Liability (-GA)]

Claim Scenarios & Reporting Syntax

Clinical & Billing Scenario	Proper Coding & Modifier Structure
Standard PT Visit (Under Threshold)	`97110-GP` (Therapeutic exercise delivered directly by PT)
Standard OT Visit (Under Threshold)	`97530-GO` (Therapeutic activity delivered directly by OT)
Standard SLP Treatment	`92507-GN` (Speech/language therapy delivered by SLP)
PTA Providing Services (>10% Time)	`97110-GP-CQ` (PT plan of care; PTA-delivered $\to$ 85% reimbursement)
OTA Providing Services (>10% Time)	`97535-GO-CO` (OT plan of care; OTA-delivered $\to$ 85% reimbursement)
Threshold Exceeded (PT Direct)	`97116-GP-KX` (Gait training; expenses >$2,480; medical necessity certified)
Threshold Exceeded (PTA Delivered)	`97110-GP-CQ-KX` (PTA-delivered service exceeding statutory threshold)
Same-Day PT & OT on Same Patient	Line 1: `97110-GP` (PT) Line 2: `97530-GO` (OT)
NCCI Mutually Exclusive Pair (Distinct Body Part)	`97140-GP` (Manual therapy, cervical) + `97530-GP-59` or `-XS` (Separate limb/site)
Maintenance Therapy (Non-Skilled, ABN Signed)	`97110-GP-GA` (Patient liable upon Medicare medical necessity denial)

7. Clinical Documentation Requirements

Under CMS Benefit Policy Manual Chapter 15, §220, documentation must substantiate each appended modifier:

Certified Plan of Care (POC):
- Established before treatment begins; signed and dated by the qualified therapist.
- Certified (physician/NPP signature) within 30 calendar days of initial evaluation.
- Recertification required at least every 90 calendar days or when significant changes occur.
Discipline-Specific Clinical Justification:
- Clearly delineate physical therapy vs. occupational therapy vs. speech therapy goals.
- Objective baseline measurements, measurable functional goals, and documented skilled interventions (preventing duplicate billing between concurrent PT and OT).
Timed Minutes Record (The 8 Minute Rule):
- Document both Total Timed Treatment Minutes and Total Overall Session Time.
- Clear documentation of who provided each minute of service (PT vs. PTA) to substantiate -CQ / -CO application.
-KX Modifier Justification:
- Explicit clinical notes outlining why the patient requires skilled care beyond the $2,480 threshold (e.g., post-operative complexity, high fall risk, severe neurological deficit, multi-trauma).

8. Compliance Warnings & Audit Pitfalls

Critical PM&R Audit Triggers

Cross-Discipline Mismatch: Billing OT codes with -GP or PT codes with -GO. Never apply -GP to OT or SLP plan of care lines.

Omission of -GP/-GO/-GN on Evaluation Codes: Many practices mistakenly believe modifiers only apply to treatment codes. Omission of -GP on 97161–97163 results in automatic front-end claim rejections.

Failure to Report -CQ / -CO: Failing to report PTA/OTA modifiers when assistants perform $> 10%$ of care constitutes improper billing and false claims exposure under the MPFS 15% payment differential.

Inappropriate Code Selection (e.g., 97110 with -GN): Billing CPT 97110-GN (Therapeutic exercise by an SLP) is an audit trigger. SLPs must bill speech/language/cognitive/swallowing CPT codes within their statutory scope of practice (e.g., 92507, 92526, 97129).

Routine KX Appending: Appending -KX as an automated billing rule without verifying whether the threshold has been reached or without clinical justification documented in the chart constitutes fraudulent attestation.

Clinical MOC & specialty guides:
Individual Modifier Files:
- -GP — Services under PT plan of care
- -GO — Services under OT plan of care
- -GN — Services under SLP plan of care
- -CQ — Services by PTA (15% reduction)
- -CO — Services by OTA (15% reduction)
- -KX — Medical policy requirements met (Therapy threshold)
- 50 Medical Coding/Modifiers/Modifiers

Regulatory citations: CMS IOM Pub. 100-04, Ch. 5; CMS IOM Pub. 100-02, Ch. 15, §§220-230; 42 CFR §414.64; CMS Calendar Year 2026 Medicare Physician Fee Schedule (MPFS) Final Rule. Verify local MAC LCD policies for jurisdiction-specific medical necessity criteria.

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Therapy Modifiers (-GP, -GO, -GN, -CQ, -CO, -KX) - PM&R Coding Reference