CPT Modifier Quick Reference for Therapy
A short reference for the modifiers PT, OT, and SLP clinicians append most often. Plain-language summaries only — this is a memory aid, not a coding policy. Modifier requirements vary by payer, state, and setting, so confirm against your payer’s current guidance and the official sources listed below before you bill.
Common therapy modifiers
| Modifier | Type | What it signals |
|---|---|---|
GP | Discipline | Services delivered under an outpatient physical therapy plan of care. |
GO | Discipline | Services delivered under an outpatient occupational therapy plan of care. |
GN | Discipline | Services delivered under an outpatient speech-language pathology plan of care. |
KX | Threshold | Attests that the requirements in the medical policy are met and the services are medically necessary. In outpatient therapy this is the modifier used once a beneficiary passes the annual therapy threshold. |
59 | Distinct service | Distinct procedural service — identifies a procedure that was separate and independent from another service on the same day. Many payers now prefer the more specific X modifiers below where one applies. |
XE | Distinct service | Separate encounter. A subset of 59 used when the services happened during distinct encounters on the same day. |
XS | Distinct service | Separate structure. A subset of 59 used when the services were performed on a different organ or body structure. |
XP | Distinct service | Separate practitioner. A subset of 59 used when a different practitioner performed the service. |
XU | Distinct service | Unusual non-overlapping service. A subset of 59 for a service that does not overlap the usual components of the main service. |
CQ | Assistant | Outpatient physical therapy services furnished in whole or in part by a physical therapist assistant. |
CO | Assistant | Outpatient occupational therapy services furnished in whole or in part by an occupational therapy assistant. |
GA | Liability | A waiver of liability statement (an ABN) is on file, and the provider expects the service may be denied as not reasonable and necessary. |
GY | Liability | The item or service is statutorily excluded or does not meet the definition of a Medicare benefit. |
GZ | Liability | The provider expects the service to be denied as not reasonable and necessary, and no ABN was issued. |
96 | Habilitative / rehabilitative | Habilitative service — helps a patient learn a skill or function they had not previously developed. |
97 | Habilitative / rehabilitative | Rehabilitative service — helps a patient regain a skill or function they had lost. |
52 | Extent of service | Reduced services — the procedure was partially reduced or eliminated at the provider’s discretion. |
22 | Extent of service | Increased procedural services — the work required was substantially greater than typical. Expect to submit documentation. |
How to use this sheet
Discipline modifiers (GP, GO, GN) identify the plan of care and are the ones you attach most routinely. The distinct-service family (59 and the X modifiers) exists to explain why two services that would normally bundle were genuinely separate — reach for the specific X modifier when one fits, and keep documentation that supports it. The liability modifiers (GA, GY, GZ) describe what you told the patient about coverage, not what you did clinically.
None of these change how many units you bill. If you are working out units from treatment minutes, start with the calculators below.
Related tools
Official sources
- CMS, Medicare Claims Processing Manual, Chapter 5 — outpatient rehabilitation billing, including therapy modifiers and the threshold.
- CMS MLN Booklet, Outpatient Rehabilitation Therapy Services — plain-language overview of therapy billing requirements.
- APTA, Coding and Billing — discipline-specific guidance and updates.
- AMA, Current Procedural Terminology (CPT) — the authoritative CPT code set and modifier definitions.