Physical therapy billing requires mastery of Medicare's 8-minute rule, timed vs. untimed code distinctions, annual therapy thresholds, and KX modifier compliance—rules that directly determine how many units can be billed for every treatment session. VeriMedix ensures PT practices capture all billable units while maintaining the documentation integrity that protects against audits and denials.
Physical therapy billing is built around a fundamental distinction between timed codes and untimed (service-based) codes. Timed codes—such as 97110 (therapeutic exercises), 97112 (neuromuscular reeducation), 97140 (manual therapy), and 97530 (therapeutic activities)—are billed in 15-minute increments and subject to the 8-minute rule. Untimed codes—such as 97010 (hot/cold packs), 97014 (unattended electrical stimulation), 97161–97163 (PT evaluations), and 97150 (group therapy)—are billed once per session regardless of how long they take. Correctly categorizing each service and applying the 8-minute rule to aggregate timed minutes is the foundation of accurate PT billing.
The Medicare 8-minute rule requires therapists to count total timed service minutes per session and bill one unit for each full 15-minute increment, plus one additional unit if at least 8 minutes remain. For example, 38 minutes of timed service = 3 billable units (38 ÷ 15 = 2 full units plus 8 minutes remaining, which meets the 8-minute threshold for a third unit). The GP modifier is required on all claims for physical therapy services, signaling to Medicare that the service is under a physical therapist's plan of care. When a physical therapy assistant (PTA) performs at least 10% of a service, the CQ modifier must be appended to denote PTA-delivered care, and payment is reduced to 85% of the standard fee schedule rate. The CO modifier serves the same function for occupational therapy assistants.
Medicare's annual therapy threshold—$2,410 for PT and SLP combined in 2025 ($2,480 in 2026)—triggers the KX modifier requirement once a patient's cumulative therapy expenses reach that threshold. Adding KX to each claim line attests that continued therapy is medically necessary and that appropriate documentation exists in the medical record. Claims exceeding the threshold without KX are automatically denied. A higher targeted medical review threshold of $3,000 activates additional claims scrutiny. Plan of care certification requirements mandate that a physician, NP, or PA certify (sign) the therapist's plan of care within a defined timeframe—typically within 30 days of the evaluation.
Below are commonly billed codes our certified coders manage for physical therapy practices. Always confirm payer-specific coverage and current code values.
| Code | Description | Billing note |
|---|---|---|
97161 | Physical therapy evaluation, low complexity | Untimed; billed once per initial evaluation; documents low-complexity clinical presentation |
97162 | Physical therapy evaluation, moderate complexity | Untimed; moderate clinical presentation with established body structure or function impairment |
97163 | Physical therapy evaluation, high complexity | Untimed; high-complexity presentation with multiple body system involvement |
97110 | Therapeutic exercises; each 15 minutes | Timed; one-on-one skilled instruction; subject to 8-minute rule; one of highest-volume PT codes |
97112 | Neuromuscular reeducation of movement, balance, coordination, kinesthetic sense; each 15 minutes | Timed; document specific neuromuscular deficits being treated |
97140 | Manual therapy techniques (e.g., mobilization/manipulation, manual lymphatic drainage, manual traction); each 15 minutes | Timed; cannot be billed with 97124 (massage) even with modifier 59 per NCCI mutually exclusive edit |
97530 | Therapeutic activities, direct one-on-one patient contact; each 15 minutes | Timed; use when functional tasks are the treatment focus; can be billed same session as 97140 with modifier 59 if in distinct 15-minute intervals |
97010 | Application of a modality to one or more areas; hot or cold packs | Untimed; service-based; typically not separately reimbursable by Medicare as standalone service |
97164 | Re-evaluation of physical therapy established plan of care | Untimed; bill only when there are new clinical findings, treatment failure, or unanticipated significant change in status |
Our standard operating procedures for physical therapy revenue cycle management — the step-by-step workflow we follow on every claim:
These are the issues we see most often in physical therapy billing — and exactly how we resolve them:
Billing one unit per timed code rather than calculating units from total timed minutes per session is a common and systematic error in PT billing. Example: billing 1 unit of 97110 for 20 minutes and 1 unit of 97140 for 18 minutes = 2 units, but the correct calculation (38 total timed minutes) supports 3 units. Fix: implement session-by-session unit calculation in the billing system or EHR using the aggregate minute rule; train therapists to document exact minutes per timed service.
Claims for patients who have reached the annual Medicare therapy threshold ($2,410 in 2025) submitted without the KX modifier are automatically denied by CMS. Fix: configure the billing system to automatically alert when a patient's year-to-date PT/SLP charges approach the threshold; require confirmation that documentation of medical necessity is on file before the KX modifier is added to claims.
Medicare requires that the plan of care be certified (signed) by a physician, NP, or PA before or within a defined period following the start of care. Claims submitted without a completed certification are denied. Fix: establish a workflow to send POC documents to the certifying provider immediately after the initial evaluation; track unsigned POCs daily and hold billing for uncertified plans until signed certification is received.
All Medicare physical therapy claims must include modifier GP. Omitting it causes denial or misrouting of the claim. Fix: build a billing rule that automatically appends GP to all claim lines when the claim is for Medicare and the treating provider is a licensed physical therapist or PTA.
CPT 97124 and 97140 are a mutually exclusive NCCI edit pair and cannot be billed together under any circumstances—no modifier can override this restriction per CMS policy. Fix: add a hard NCCI edit in the billing scrubber that prevents simultaneous submission of 97124 and 97140 on the same date for the same patient.
Verimedix works inside the systems physical therapy practices already use, including:
Under CMS guidelines, add together the total minutes of all timed services provided during the session, then calculate units from that total: 8–22 minutes = 1 unit; 23–37 minutes = 2 units; 38–52 minutes = 3 units; 53–67 minutes = 4 units, and so on. Allocate those units among the timed codes proportionally by time spent. Commercial payers may follow the AMA's per-code rule (8 minutes per code = 1 unit per code) rather than the CMS aggregate rule—verify each payer's method.
The KX modifier threshold ($2,410 for PT/SLP combined in 2025) is the point at which a KX modifier must be appended to all claims to confirm medical necessity. The targeted medical review threshold ($3,000 in 2025) is a separate, higher threshold above which CMS may initiate focused review of the patient's therapy claims to verify medical necessity. Both thresholds reset each calendar year and apply separately to PT/SLP versus OT services.
No. CPT 97164 (PT re-evaluation) is appropriate only when the clinical record documents: new clinical findings not addressed in the current plan of care, failure to respond to treatment as expected, or a significant, unanticipated improvement or decline in the patient's functional status. Routine progress notes or periodic reassessments within the current plan of care do not support billing 97164. Misuse of re-evaluation codes is a common audit finding.
Track time separately for PT and PTA minutes per service. If the PTA provides at least 10% of a given timed service, the CQ modifier must be appended to that service code. If the PT provides the majority (more than 50% of that specific service's minutes), the unit is billed without CQ. CMS pays CQ-modified services at 85% of the standard rate. Document in the session note which portions of the treatment were delivered by the PT versus the PTA, with minutes recorded.
Not universally. Many commercial payers follow the AMA's per-code rule, which allows billing one unit for each code when at least 8 minutes of that specific service were provided—rather than calculating units from the session's aggregate timed minutes. Always verify payer-specific billing guidelines. For Medicare and most Medicare Advantage plans, the CMS aggregate 8-minute rule applies.
For each timed CPT code billed, the clinical note must document: the specific procedure performed (matching the CPT code description), the start and end time (or total minutes), the patient's response to treatment, and the clinical rationale for the skilled therapy service. For any session exceeding the KX modifier threshold, additional documentation of continued medical necessity and functional progress toward measurable goals is required in the record.
WebPT is the most widely adopted outpatient physical therapy EHR and billing platform in the US, purpose-built for the specialty. Clinicient (now Raintree Systems), Prompt, Fusion Web Clinic, and TheraOffice are other popular PT-specific platforms. Larger health systems may use Epic or Cerner with therapy-specific modules. The EHR must support documentation of timed minutes per service, modifier management, KX threshold tracking, and POC certification workflows.
Verimedix handles the entire physical therapy revenue cycle — coding, submission, denials, and A/R — so your team can focus on patients.