Physical Therapy Billing Resource Center
Physical therapy billing involves unique challenges — the Medicare 8-minute rule, therapy caps, KX modifiers, and complex CPT code requirements. This resource center provides the reference guides you need to reduce denials and maximize reimbursement.
Quick Answer
Physical therapy billing involves specialized rules including the 8-minute rule for time-based codes, the KX modifier for therapy thresholds, the GP modifier for physical therapy services, and prior authorization for certain PT procedures. PT claims are frequently denied for missing modifiers, exceeding therapy caps, and lacking prior auth.
Key Takeaways
The 8-minute rule determines how to bill time-based PT codes.
The KX modifier is required when exceeding the therapy threshold (formerly therapy cap).
The GP modifier indicates physical therapy services.
PT prior authorization is required for certain procedures by some payers.
Common PT denial codes: CO-16 (missing modifier), CO-151 (utilization), CO-197 (missing auth).
Step-by-Step
Apply the 8-minute rule
Count total treatment minutes. Divide by the unit value. Bill full units for 8+ minutes remaining, and the code with the most time gets the extra unit.
Append the GP modifier
The GP modifier indicates the service was provided by a physical therapist. It is required on all PT CPT codes.
Monitor therapy thresholds
Track therapy minutes against the annual threshold. When exceeded, append the KX modifier to indicate medical necessity above the threshold.
Check prior auth requirements
Some payers require prior auth for certain PT procedures. Verify before rendering the service.
Common Mistakes
Not applying the 8-minute rule correctly — causes overbilling or underbilling.
Forgetting the GP modifier — causes CO-16 denials.
Not appending KX when exceeding the therapy threshold — claims denied.
Not tracking therapy minutes against the annual threshold.
FAQ
Related Resources
Common Denials
Top Physical Therapy Denial Codes
| Code | Description | Resolution |
|---|---|---|
| CO-97 | Service bundled | Check NCCI edits; remove bundled code |
| CO-50 | Non-covered service | Verify medical necessity; appeal with documentation |
| CO-197 | Authorization absent | Obtain prior auth for therapy visits |
| CO-16 | Missing information/modifier | Add GP, KX, or other required modifiers |
| CO-151 | Frequency limit exceeded | Apply KX modifier if threshold met with justification |
| CO-45 | Contractual adjustment | Write off per contract; no patient liability |
8-Minute Rule
Medicare 8-Minute Rule Calculation
Medicare requires timed modalities to be billed based on the total treatment time.
| Service | CPT Code | Time | Units |
|---|---|---|---|
| Therapeutic Exercise | 97110 | 23 min | 2 units |
| Manual Therapy | 97140 | 16 min | 1 unit |
| Electrical Stimulation | 97014 | 8 min | 1 unit |
| Total Session | 47 min | 4 units |
8-Minute Rule: One unit = 8-22 min, two units = 23-37 min, three units = 38-52 min. Remainder must be ≥8 min to bill an additional unit.
Key Modifiers
Essential PT Billing Modifiers
GP Modifier
Indicates services delivered under a physical therapy plan of care. Required on all PT claims for most payers, especially Medicare.
KX Modifier
Indicates the patient has exceeded the Medicare therapy cap but services are medically necessary and justified. Must include supportive documentation.
59 Modifier
Distinct procedural service. Used when performing services that are normally bundled but are separately appropriate in this case.
GO / GN Modifiers
GO = occupational therapy plan of care. GN = speech-language pathology plan of care. Used to identify the therapy discipline for the claim.
Frequently Asked Questions
Physical Therapy Billing FAQ
What is the Medicare 8-minute rule for physical therapy?
The Medicare 8-Minute Rule determines how to bill timed therapy services. For each timed CPT code, count the total minutes spent. One unit = 8-22 minutes, two units = 23-37 minutes, three units = 38-52 minutes, four units = 53-67 minutes. The remainder of minutes after the first unit must be at least 8 minutes to bill an additional unit. For example, if you spend 23 minutes on therapeutic exercise (97110), you bill 2 units. If you spend 21 minutes, you bill 1 unit. Untimed services (evaluation, re-evaluation) are billed as one unit regardless of duration.
What is the KX modifier and when is it used?
The KX modifier is used when a Medicare patient exceeds the annual therapy cap (the threshold for physical therapy and speech-language pathology combined). By appending the KX modifier, the provider attests that the services are medically necessary and justified despite exceeding the cap. The modifier must be supported by documentation in the medical record showing why continued therapy is necessary. Without the KX modifier, Medicare will deny claims that exceed the cap. The cap amount changes annually.
What are the most common physical therapy CPT codes?
Common physical therapy CPT codes include: 97110 (Therapeutic Exercise), 97112 (Neuromuscular Reeducation), 97113 (Aquatic Therapy), 97116 (Gait Training), 97140 (Manual Therapy), 97150 (Therapeutic Procedures, Group), 97010 (Hot/Cold Packs, untimed), 97014 (Electrical Stimulation, untimed), 97035 (Ultrasound), 97161-97164 (PT Evaluation — low, moderate, high complexity), and 97110 (Therapeutic Exercise). Each timed code is billed based on the 8-minute rule.
Does physical therapy require prior authorization?
Whether PT requires prior authorization depends on the payer and plan. Medicare typically does not require prior authorization for outpatient PT. However, many commercial payers — particularly Medicare Advantage plans, managed Medicaid, and some commercial plans — require prior authorization for physical therapy, often after a set number of visits (e.g., 6, 8, or 12 visits). Always verify authorization requirements at the time of eligibility verification. Failure to obtain required authorization is a leading cause of PT denials (CO-197).
What is the GP modifier and when is it required?
The GP modifier indicates that services were delivered under a physical therapy plan of care. The GO modifier indicates occupational therapy, and the GN modifier indicates speech-language pathology. Medicare and many commercial payers require these modifiers on all therapy claims to identify the discipline providing the service. Claims submitted without the correct therapy modifier may be denied or processed incorrectly.