Rehabilitation billing covers physical therapy (PT), occupational therapy (OT), and speech-language pathology (SLP) services.
It differs from general medical billing because therapy claims depend on timed CPT codes, the 8-minute rule, therapy-specific modifiers (GP, GO, GN, KX, CQ, CO), and Medicare utilization thresholds that don’t apply to other specialties.
The OIG has identified outpatient therapy as a high-risk audit category, with improper payments tied to missing documentation, insufficient medical necessity support, and incomplete plans of care.
In this guide, we’ll be exploring:
- Correct rehabilitation CPT codes
- Medicare documentation and threshold rules
- Therapy modifiers and when each is required
- The 8-minute rule and how timed units are calculated
- The six denial patterns that cost therapy practices the most
What are the correct rehabilitation CPT codes?
Rehab CPT codes fall into three groups — evaluation codes, timed procedure codes, and modality codes.
Evaluation codes
Here are the evaluation CPT codes:
| CPT code | Description |
| 97161–97163 | PT evaluation (low, moderate, high complexity) |
| 97164 | PT re-evaluation |
| 97165–97167 | OT evaluation (low, moderate, high complexity) |
| 97168 | OT re-evaluation |
Timed procedure codes
A list of timed procedure codes:
| CPT code | Correct description |
| 97110 | Therapeutic exercises (strength, endurance, ROM, flexibility) |
| 97112 | Neuromuscular reeducation |
| 97116 | Gait training |
| 97140 | Manual therapy (mobilization, manipulation) |
| 97530 | Therapeutic activities (functional tasks) |
| 97535 | Self-care/home management training |
Modality codes
A list of modality codes:
| CPT code | Description |
| 97010 | Hot/cold packs (Medicare generally bundles) |
| 97014 | Electrical stimulation (unattended) |
| 97032 | Electrical stimulation (attended, manual — timed) |
| 97035 | Ultrasound therapy (timed) |
Here’s a chart you can use for reference:
Quick Reference
Correct Therapy CPT Codes
Verified against AMA CPT and CMS guidance.
Therapeutic Exercise
Manual Therapy
Neuromuscular Reeducation
Gait Training
Therapeutic Activities
Self-Care/Home Management
How does the 8-minute rule work?
The 8-minute rule is the CMS calculation method for timed therapy codes. Under Medicare Claims Processing Manual, Chapter 5, at least 8 minutes of direct one-on-one treatment is required to bill one unit.
| Total minutes | Billable units |
| 8–22 | 1 unit |
| 23–37 | 2 units |
| 38–52 | 3 units |
| 53–67 | 4 units |
When multiple timed services are provided in the same session (97110 + 97140 + 97112), total treatment minutes across all timed codes determine maximum billable units. Individual code minutes are allocated using the “rule of eights” — each code needs at least 8 minutes documented.
Common 8-minute errors
- Billing 1 unit for 7 minutes of treatment (doesn’t meet the 8-minute minimum)
- Billing more units than total treatment time supports
- Failing to document actual minutes per timed code
In practice, the 8-minute rule is where the most therapy audit findings originate — not because therapists don’t provide enough treatment time, but because the time documentation doesn’t match the units billed.
A therapist who provides 45 minutes of treatment but documents “4 units” without breaking down the minutes per code creates a denial on audit.
Which therapy modifiers are required?
Every rehab claim requires a discipline modifier (GP/GO/GN), and Medicare claims above the utilization threshold need KX. Missing GP/GO/GN is the single most common modifier denial in therapy billing.
| Modifier | When required |
| GP | Every PT claim |
| GO | Every OT claim |
| GN | Every SLP claim |
| KX | When charges exceed the annual Medicare utilization threshold |
| CQ | Service performed by a PT assistant |
| CO | Service performed by an OT assistant |
| 59 / XS | Manual therapy (97140) billed with other therapy codes at a different site |
| 25 | E/M billed on same day as therapy |
Missing GP/GO/GN
The most common modifier denial in rehab billing. Without the discipline modifier, the payer can’t identify the service as therapy and the claim is denied. Build the appropriate modifier into billing system defaults.
KX threshold
The Medicare therapy cap was repealed in 2018, but CMS replaced it with an annual utilization threshold. When therapy charges exceed the threshold (updated annually), KX must be appended to indicate medical necessity. Claims above a higher “targeted medical review” threshold may be selected for manual review by MACs.
What ICD-10 codes support rehabilitation claims?
Here is a list of ICD-10 codes for rehab claims:
| ICD-10-CM | Description |
| M54.50 / M54.51 | Low back pain (unspecified / vertebrogenic) |
| M54.2 | Cervicalgia |
| M54.6 | Pain in thoracic spine |
| M17.0 | Bilateral primary osteoarthritis, knee |
| M62.81 | Muscle weakness, generalized |
| G81.90 | Hemiplegia, unspecified |
| I63.9 | Cerebral infarction (stroke) |
| S72.001A | Fracture of neck of femur, initial |
Diagnosis specificity affects medical necessity validation. A claim for 12 weeks of PT supported by “M54.9 — dorsalgia, unspecified” is weaker than one supported by “M54.51 — vertebrogenic low back pain” with documented functional limitations.
What does Medicare require for therapy claims?
Medicare Part B covers outpatient PT, OT, and SLP when medically necessary, documented in a physician-certified plan of care, and recertified every 90 days. Claims without these elements are denied on audit — even when the treatment itself was appropriate.
Plan of care
A physician-certified plan with diagnosis, long-term goals, and treatment type/frequency. Recertification every 90 days.
Visit documentation
Medical necessity documented at every visit, with functional progress notes showing improvement or justifying continued treatment. The OIG has identified therapy claims lacking sufficient documentation as a persistent source of improper Medicare payments.
Denial Prevention
Top Rehab Billing Denials
What should benefits verification cover for therapy?
Rehab claims are denied more often for authorization and eligibility failures than for coding errors.
A therapy-specific verification should confirm visit limits per benefit period, remaining deductible, copay and coinsurance, PA requirements (and for how many visits), whether the plan separates PT/OT/SLP visit limits, and whether a physician referral is required.
The AMA’s 2024 prior authorization survey found that 94% of physicians reported PA delays in care. For therapy practices, authorization management is the front-end workflow that determines whether treatment sessions will be reimbursable at all.
Your therapy sessions shouldn’t lose money in the billing queue
Most rehab denials trace back to modifier omissions, 8-minute rule miscalculations, expired authorizations, or plan-of-care gaps. These aren’t coding complexity problems — they’re workflow gaps that repeat across every session.
MedHeave builds therapy-specific billing controls into the claim workflow — timed code accuracy, GP/GO/GN defaults, KX threshold tracking, authorization management, and the documentation standards that OIG auditors review.
- Dedicated account managers with direct access
- Claims submitted within 24–48 hours of signed session notes
- Performance-based pricing (4–7% of collections) with no lock-in
- Denials addressed within 72 hours with payer-specific documentation
Contact us to see how structured rehab billing captures the full value of every therapy session delivered.
Frequently asked questions
Here are some commonly asked questions on this topic:
Rehabilitation billing translates therapy services into standardized timed CPT codes, links them to ICD-10 diagnosis codes, applies therapy-specific modifiers (GP for PT, GO for OT, GN for SLP), and submits claims to payers for reimbursement. Timed codes require at least 8 minutes of direct one-on-one treatment per billable unit under CMS rules. Claims must be supported by a physician-certified plan of care, documented medical necessity, and functional progress notes showing improvement.
The 8-minute rule is the CMS calculation method for timed therapy CPT codes. A minimum of 8 minutes of direct one-on-one treatment is required to bill one unit. When multiple timed services are provided in the same session, total treatment minutes determine the maximum billable units — one unit for 8–22 minutes, two for 23–37, three for 38–52, and so on. Documenting actual treatment minutes per code is required, and billing units that exceed documented time is a compliance violation.
Every therapy claim requires a discipline modifier — GP (physical therapy), GO (occupational therapy), or GN (speech-language pathology). The KX modifier is required when Medicare therapy charges exceed the annual utilization threshold to certify medical necessity. CQ and CO identify services performed by PT assistants and OT assistants respectively. Modifier 59/XS applies when manual therapy (97140) is billed as a distinct service. Modifier 25 is required for same-day E/M visits.
PT evaluations use CPT 97161 (low complexity), 97162 (moderate complexity), 97163 (high complexity), and 97164 (re-evaluation). Level selection depends on clinical complexity — number of body systems examined, comorbidity impact, and clinical decision-making documented in the evaluation. The former evaluation codes 97001 and 97002 were deleted in 2017 and are rejected by every payer. Claims submitted with deleted codes produce automatic rejections.
Medicare Part B covers outpatient PT, OT, and SLP services when medically necessary, performed by a licensed therapist, and documented in a physician-certified plan of care. Coverage continues as long as the patient shows measurable functional progress. The therapy cap was permanently repealed in 2018, but CMS replaced it with an annual utilization threshold (requiring the KX modifier) and a targeted medical review threshold above which claims may be selected for manual review by MACs.
