Crystal's MCW Coder Hub⚕️ Modifier GP: Services Delivered Under an Outpatient Physical Therapy Plan of Care
Quick Reference
Descriptor: Services Delivered Under an Outpatient Physical Therapy Plan of Care 1 Global Period: N/A — follows the global period of the billed PT CPT® code 2 Provider Type: Physical Therapist (PT) / Physical Therapy Assistant (PTA) under PT supervision 3 Reimbursement: Paid at Medicare Physician Fee Schedule rate for PT services when medically necessary 4 NCCI Status: Required on all PT services billed to Medicare Part B; Modifier Indicator 1 5 Approach: Appended to every PT CPT® or HCPCS code on each line of the claim
📋 Code Description & Clinical Context
Modifier -GP is a Level II HCPCS modifier that identifies services performed under an outpatient physical therapy plan of care 1. Because many therapy CPT® codes are shared across physical therapy (PT), occupational therapy (OT), and speech-language pathology (SLP), Medicare requires discipline-specific modifiers to accurately track utilization, apply the correct payment thresholds, and determine which therapy type delivered the service 6. Without -GP, Medicare cannot process a physical therapy claim correctly and will deny it.
The three therapy discipline modifiers are:
Key Usage Indications:
- All PT evaluation and re-evaluation codes (97161, 97162, 97163, 97164)
- All PT treatment procedure codes on the same date of service (97110, 97112, 97116, 97140, 97530, 97535, 97542, 97750, 97760, 97761, 97763)
- Group therapy billed by a PT (97150)
- Aquatic therapy (97113) billed under a PT plan of care
- RTM monitoring codes billed under a PT plan (98975, 98976, 98977, 98980, 98981)
- HCPCS G-codes for PT services (e.g., G0283)
- PT services billed in SNF Part B, outpatient hospital, private clinics, patient home (not under home health), and telehealth
Every Line Item — No Exceptions
🌲 Code Hierarchy / Context
HCPCS Level II Modifiers
└─ Therapy Discipline Modifiers
├─ -GP Services Under PT Plan of Care ← THIS MODIFIER
├─ -GO Services Under OT Plan of Care
├─ -GN Services Under SLP Plan of Care
└─ -KX Therapy Threshold Exception (co-billed with -GP when threshold exceeded)
Parent Category: Therapy Discipline Modifiers (HCPCS Level II) 7 Related Modifiers: -GO (OT), -GN (SLP), -KX (therapy threshold attestation, co-billed with -GP), -GA (ABN on file, co-billed with -GP when Medicare likely to deny), -59 (distinct service when needed on timed code pairs) Primary Code Dependency: Must be appended to a valid PT CPT® or HCPCS code on a CMS-1500 / 837P claim
💰 Reimbursement & Valuation
| Component | Rate | Notes |
|---|---|---|
| Base Rate | 100% | Paid at Medicare Physician Fee Schedule (MPFS) for the billed PT CPT® code 4 |
| PTA Reduction | 85% | When a PTA provides services under PT supervision, append -CQ alongside -GP; paid at 85% of MPFS 4 |
| Therapy Threshold (2026) | $2,330 (PT/SLP combined) | When exceeded, -KX must be appended alongside -GP to attest to continued medical necessity 8 |
| Targeted Medical Review Trigger | $3,000 | Claims may be selected for medical review once therapy costs surpass this amount 8 |
| Medicare Advantage | Follows original Medicare | Most MA plans follow CMS rules; confirm individual plan requirements 6 |
| Telehealth | GP required | -GP applies to PT telehealth services; additional telehealth modifiers also required 3 |
Assistant/Support Modifier Note:
- When a Physical Therapy Assistant (PTA) delivers the service, append -CQ alongside -GP on every affected line — payment reduces to 85% of MPFS 4
- When a student PT (not yet licensed) furnishes services in whole or in part, append -CO alongside -GP — payment reduces to 85% 4
🚫 Includes / Excludes & NCCI Guidance
✅ Includes
- All PT evaluation codes (97161–97164) 3
- All PT procedure codes (timed and untimed) performed under a PT plan of care 3
- Group PT therapy (97150) 3
- Aquatic therapy (97113) performed under a PT plan of care
- RTM supply (98976, 98977) and monitoring management codes (98980, 98981) when under PT plan 9
- HCPCS G0283 (Electrical stimulation for wound care, billed under PT plan by chiropractors/PTs) 10
- SNF Part B long-term care resident PT claims (not under a Part A stay) 3
- Telehealth PT services (also requires applicable telehealth modifier) 3
❌ Excludes / Not Used With -GP
- SNF Part A covered stay: Therapy is bundled into facility payment; facility bills Medicare, not the individual PT 3
- Home health episode: Under a Medicare home health plan of care, the HHA bills therapy services; -GP is not separately appended by the individual PT 3
- OT or SLP services: Those services require -GO and -GN respectively — do NOT apply -GP to non-PT discipline codes 6
- CPT® codes that describe a series or protocol by definition that are beyond the scope of outpatient PT (e.g., physician-only E/M codes, surgical procedures, non-therapy HCPCS)
- Modifier -GY: Statutory exclusion — if a service is excluded by statute, -GP cannot make it billable
Do Not Mix Discipline Modifiers
🏥 MS-DRG Assignment (Inpatient Facility)
Modifier -GP is used exclusively on outpatient professional (Part B) claims and does not apply to inpatient MS-DRG assignment. However, the diagnoses supporting the PT plan of care are critical to ensuring appropriate care coordination documentation across care settings.
| Scenario | Impact | Description |
|---|---|---|
| Post-acute outpatient PT after hospital discharge | No DRG impact | -GP applies to post-discharge Part B claims only 11 |
| SNF Part B PT (long-term resident) | No DRG impact | Billed directly to Medicare Part B with -GP; facility Part A not affected 3 |
| Therapy threshold exceeded | KX required | Add -KX alongside -GP; no DRG effect but impacts Part B payment 8 |
| Documentation supports functional diagnosis | Supports CC/MCC on prior inpatient stay | Diagnoses like M54.50, G81.91, S72.001A may have been CC/MCC during inpatient stay 12 |
Note
Facility reimbursement (Part A / MS-DRG) is not affected by modifier -GP. This modifier is a Part B professional billing element only 11.
🏷️ Common ICD-10-CM Diagnosis Codes
Modifier -GP* does not change diagnosis coding requirements. The diagnosis must support the medical necessity of the physical therapy plan of care and the specific PT services billed.*
Primary Diagnosis Options (Supporting PT Plan of Care)
| ICD-10-CM Code | Description | HCC Status* |
|---|---|---|
| M54.50 | Low back pain, unspecified | ❌ Not HCC |
| M17.11 | Primary osteoarthritis, right knee | ❌ Not HCC |
| M17.12 | Primary osteoarthritis, left knee | ❌ Not HCC |
| S72.001A | Fracture of unspecified part of neck of right femur, initial encounter | ❌ Not HCC |
| G81.91 | Hemiplegia, unspecified, affecting right dominant side | ✅ HCC (Neurological) |
| G35 | Multiple sclerosis | ✅ HCC (Neurological) |
| G20 | Parkinson’s disease | ✅ HCC (Neurological) |
| I69.351 | Hemiplegia and hemiparesis following cerebral infarction affecting right dominant side | ✅ HCC (Stroke/Neuro) |
| Z96.641 | Presence of right artificial hip joint (post-THA PT) | ❌ Not HCC |
| Z96.651 | Presence of right artificial knee joint (post-TKA PT) | ❌ Not HCC |
* HCC Status: Hierarchical Condition Category mapping for Medicare Advantage risk adjustment. The diagnosis — not the modifier — drives HCC assignment. Modifier -GP has no direct impact on risk scores 1314.
Supporting/Comorbid Codes (Document When Applicable)
- R26.89 Other abnormalities of gait and mobility (supports gait training 97116)
- M62.81 Muscle weakness, generalized (supports therapeutic exercise 97110)
- R53.1 Weakness (supports neuromuscular re-education 97112)
- Z87.39 Personal history of musculoskeletal disorders (supports continued PT)
- Z96.641 / Z96.651 Presence of artificial joint (post-surgical PT support)
✏️ Modifiers Guidance
| Modifier | Relationship to -GP | Payable Together? |
|---|---|---|
| -GO | OT discipline modifier — mutually exclusive with -GP for same service line | ❌ Never on the same line |
| -GN | SLP discipline modifier — mutually exclusive with -GP for same service line | ❌ Never on the same line |
| -KX | Therapy threshold attestation — append alongside -GP when annual threshold exceeded | ✅ Required together when threshold exceeded |
| -GA | ABN on file — append alongside -GP when service expected to be denied but ABN is signed | ✅ Use together when ABN obtained |
| -GY | Statutory exclusion — service not a Medicare benefit | ❌ Mutually exclusive; if GY applies, service is non-covered |
| -CQ | Services furnished in whole or part by PTA — payment reduced to 85% | ✅ Required alongside -GP when PTA provides service |
| -CO | Services furnished in whole or part by PT student — payment reduced to 85% | ✅ Required alongside -GP when student furnishes service |
| -59 | Distinct procedural service — used on timed code pairs to prevent bundling when truly separate | ✅ May be used with -GP when appropriate |
These three modifiers are mutually exclusive on the same service line. Apply the correct discipline modifier based on who actually delivered the service under which plan of care. Misapplication leads to overpayment, audit risk, and compliance violations 6.
📝 Coding Examples
✅ Example 1: New Patient PT Evaluation + Treatment, Same Day
Scenario: New Medicare patient presents to outpatient PT clinic with left knee OA (M17.12) post-TKA (Z96.652). PT performs a moderate complexity evaluation and provides 30 min therapeutic exercise. Report:
✅ Example 2: PT and OT Same Day — Different Modifiers
Scenario: Patient with stroke (I69.351) receives PT gait training (30 min) and OT ADL training (30 min) on the same day. PT Bills:
✅ Example 3: Therapy Threshold Exceeded — KX Required
Scenario: Medicare patient with Parkinson’s (G20) has accumulated $2,330 in PT/SLP services for the year. PT continues skilled balance and gait training. Report:
❌ Example 4: Missing GP on Eval Code
Scenario: PT bills 97163 (High-Complexity Evaluation) and 97110--GP (Therapeutic Exercise) for a new patient visit. The eval code is billed without -GP. Report: 97163 (no modifier), 97110--GP Rationale: Incorrect. -GP is required on every PT code including evaluation codes. The eval line will likely deny 3.
❌ Example 5: GP Applied to OT Service Line
Scenario: A clinic bills 97535--GP (Self-Care/Home Management ADL Training — an OT service) in error. Report: 97535--GP Rationale: Incorrect. 97535 in this context is an OT service and requires -GO. Applying -GP misidentifies the discipline. Creates overpayment risk and audit exposure 6.
✅ Example 6: PTA Delivering Services — CQ Required
Scenario: A PTA under PT supervision provides therapeutic exercise (97110) and manual therapy (97140) to a Medicare patient with low back pain (M54.50). Report:
🔍 Documentation Essentials for Support
To support modifier -GP and ensure clean claims with audit readiness, documentation should include:
- Provider Credentials: Document PT name and credentials (PT, DPT, MPT) in every note 3.
- Plan of Care on File: A signed, dated PT plan of care must be established and on file before billing -GP services 7.
- Physician/NPP Certification: For Medicare, the PT plan of care must be certified (signed) by a physician or NPP within required timelines 7.
- Discipline Specificity: Notes must clearly identify the service as physical therapy (not just “therapy”). State functional goals, objective measures, and PT-specific interventions 3.
- Time for Timed Codes: Document exact start/stop times or total timed minutes per code for timed CPT® codes (8-Minute Rule compliance) 7.
- Medical Necessity: Functional limitations, objective findings, and skilled PT need must be documented in each visit note 8.
- KX Attestation (When Applicable): If -KX is co-billed, documentation must explicitly support continued skilled need beyond the threshold 8.
- ABN (When Applicable): If -GA is co-billed, a valid signed ABN must be on file prior to the date of service 15.
Documentation Language
Avoid generic entries like “therapy performed.” Use specific language: “Skilled physical therapy provided by Jane Smith, DPT, for gait training and neuromuscular re-education. Patient demonstrates measurable functional deficit in ambulation secondary to Parkinson’s disease. Today’s session focused on improving step length and balance reaction time.”
⚠️ Common Pitfalls & Audit Risks
| Pitfall | Consequence | Prevention |
|---|---|---|
| Omitting -GP from eval codes | Denial of evaluation line | Apply -GP to ALL PT codes including 97161–97164 3 |
| Using -GP on OT or SLP service lines | Overpayment, audit risk | Confirm discipline and apply -GO or -GN for non-PT services 6 |
| Failing to add -KX when threshold exceeded | Claim denial | Monitor cumulative PT/SLP costs; add -KX when $2,330 is reached 8 |
| Not appending -CQ when PTA delivers service | Overpayment at full rate | Track PTA vs PT service delivery; reduce to 85% with -CQ 4 |
| Missing or unsigned PT plan of care | Medical necessity denial | Ensure plan of care is established, certified, and updated per CMS timelines 7 |
| Vague documentation | Audit vulnerability | Use discipline-specific functional language and objective measures in every note 3 |
| Billing SNF Part A therapy with -GP | Billing error | Confirm payer source; Part A SNF therapy is bundled — do not bill separately with -GP 3 |
🔗 Related Codes & Crosswalks
| Code Type | Code | Relationship to -GP |
|---|---|---|
| HCPCS Modifier | -GO | OT discipline modifier; mutually exclusive with -GP on same service line |
| HCPCS Modifier | -GN | SLP discipline modifier; mutually exclusive with -GP on same service line |
| HCPCS Modifier | -KX | Therapy threshold exception; co-appended with -GP when threshold exceeded |
| HCPCS Modifier | -GA | ABN on file; co-appended with -GP when service expected to be denied |
| HCPCS Modifier | -CQ | PTA-delivered service; co-appended with -GP; payment at 85% |
| HCPCS Modifier | -CO | PT student-delivered service; co-appended with -GP; payment at 85% |
| CPT® | 97161 | PT Evaluation — Low Complexity; requires -GP |
| CPT® | 97162 | PT Evaluation — Moderate Complexity; requires -GP |
| CPT® | 97163 | PT Evaluation — High Complexity; requires -GP |
| CPT® | 97164 | PT Re-evaluation; requires -GP |
| CPT® | 97110 | Therapeutic Exercise (timed, 15-min units); requires -GP |
| CPT® | 97112 | Neuromuscular Re-education (timed); requires -GP |
| CPT® | 97116 | Gait Training (timed); requires -GP |
| CPT® | 97140 | Manual Therapy Techniques (timed); requires -GP |
| CPT® | 97150 | Therapeutic Procedure Group (untimed); requires -GP |
| CPT® | 97530 | Therapeutic Activities (timed); requires -GP |
| CPT® | 97535 | Self-Care/Home Management Training (timed); requires -GP when under PT plan |
| CPT® | 97750 | Physical Performance Test or Measurement; requires -GP |
| CPT® | 97760 | Orthotic Management and Training, Initial (timed); requires -GP |
| CPT® | 97761 | Prosthetic Training (timed); requires -GP |
| CPT® | 97763 | Orthotic/Prosthetic Management, Subsequent (timed); requires -GP |
| HCPCS | G0283 | Electrical stimulation (wound care) — used by PTs/chiropractors; requires -GP |
| CPT® | 98975 | RTM Setup; requires -GP when under PT plan |
| CPT® | 98976 | RTM Supply — Respiratory; requires -GP when under PT plan |
| CPT® | 98980 | RTM Management, First 20 min; requires -GP when under PT plan |
| CMS Form | CMS-1500 | Professional claim form where -GP is reported |
1 AAPC HCPCS Level II Modifier Reference — Modifier GP 2 CMS Medicare Claims Processing Manual Ch. 5 — Part B Outpatient Therapy 3 Sirius Solutions Global — Modifier GP Guide 2026: Physical Therapy Medicare Billing Rules 4 CMS Medicare Physician Fee Schedule 2026 — Therapy Services 5 CMS NCCI Policy Manual 2025 — Chapter 10 6 Medbridge — How to Use GP, KX & GA Modifiers in Therapy Billing 7 CMS Medicare Benefit Policy Manual Ch. 15 — Covered Medical and Other Health Services (Therapy) 8 APTA Medicare Payment Thresholds for Outpatient Therapy Services 2026 9 CMS Billing Examples Using CQ/CO Modifiers — RTM Services 2025 10 Illinois Chiropractic Society — Medicare Requiring Modifier GP on Physical Therapy Services 11 Medicare Claims Processing Manual Ch. 1 — General Billing Requirements 12 CMS MS-DRG Manual v41.0 13 CMS-HCC Model V28 Documentation 14 Find-A-Code HCC Mapping Tool 15 Medicare Claims Processing Manual Ch. 1 — Section 60.4.1 Outpatient Billing with an ABN