Physical therapy billing services from Medical Billing Services Group (MBSG) cover the full revenue cycle for PT clinics — from the 8-minute rule and timed-code units through KX modifier thresholds, plan-of-care certification, and payer-specific therapy policies. We handle the unit math and documentation rules that make therapy billing error-prone, so every session is billed for exactly what was furnished.
Therapy units underbilled or denied? Get a Free Billing Audit — we will review your timed-code units, KX modifier usage, and plan-of-care documentation and show you exactly where revenue is leaking.
Practice/setting fit
Our physical therapy billing services fit private PT clinics, hospital outpatient therapy departments, orthopedic practices with in-house therapy, and multispecialty groups offering rehabilitation. Physical therapy billing is built on time: most therapeutic procedures are reported in 15-minute timed units, and the number of units on the claim must follow Medicare’s unit-calculation rules exactly. A clinic that documents 38 minutes but bills 2 units instead of 3 loses a unit on every such visit; a clinic that bills 3 units for 20 minutes invites denials and audit exposure.
We manage the full revenue cycle for these settings: benefits verification with attention to therapy visit limits and thresholds, coding that follows the timed-code rules, daily claim submission with correct therapy modifiers, payment posting with contractual adjustments, and denial follow-up that goes back to the treatment note. Our coding team checks therapy claims against Medicare’s outpatient rehabilitation rules before submission, and our broader specialty billing programs cover your other service lines.
Documentation and coding risks
Therapy’s biggest billing risk is the unit count. The 8-minute rule, the distinction between timed and untimed codes, and the therapy threshold modifiers form a system where small documentation gaps compound into systematic underbilling or systematic overbilling — and both directions cost the practice.
The 8-minute rule governs every timed-code unit
Medicare calculates billable units for timed therapy codes by total treatment time: one unit for 8 through 22 minutes, two units for 23 through 37 minutes, three units for 38 through 52 minutes, and four units for 53 through 67 minutes. When multiple timed services are furnished in one visit, units are determined by total time across services, with the leftover minutes allocated per the rule — 8 or more leftover minutes earns an additional unit for the service performed longest, 7 or fewer does not. Only direct one-on-one patient contact time counts. Untimed codes (evaluations 97161–97163, reevaluation 97164, hot/cold packs) are billed once per session regardless of time and are never counted in the timed-unit math. We recalculate units from the documented minutes on every visit before the claim goes out.
Payer/program: Medicare (CMS) · Jurisdiction: United States (federal) · Source: “Medicare Claims Processing Manual, Publication 100-04, Chapter 5 — Part B Outpatient Rehabilitation and CORF/OPT Services” · Last reviewed: 2026-10-08
The KX modifier attests medical necessity above the threshold
Once a beneficiary’s incurred expenses for outpatient therapy reach the annual therapy threshold (one combined threshold for physical therapy and speech-language pathology, a separate one for occupational therapy), claims above the threshold must carry the KX modifier — which attests that the services are reasonable and necessary with supporting documentation in the medical record. Claims above the threshold without the KX modifier are denied. The threshold amount is updated annually, so the tracking must follow the current-year figure. We monitor each patient’s accumulated therapy expenses against the current threshold and append the KX modifier only where the documentation supports continued medical necessity.
Payer/program: Medicare (CMS) · Jurisdiction: United States (federal) · Source: “Medicare Claims Processing Manual, Publication 100-04, Chapter 5; CMS Therapy Services guidance (KX modifier threshold provisions)” · Last reviewed: 2026-10-08
Therapy modifiers identify the discipline and the provider type
Every PT claim carries the GP modifier to identify services furnished under a physical therapy plan of care. When a physical therapist assistant furnishes any part of the service independently of the therapist beyond the de minimis standard, the CQ modifier must also be reported — and the payment reduction applies to that portion. Assistant-furnished minutes, therapist-furnished minutes, and the de minimis calculation must all be traceable in the documentation. Missing GP modifiers, unreported CQ situations, and plans of care that lack required physician certification are among the most common preventable therapy denials we correct.
Payer/program: Medicare (CMS) · Jurisdiction: United States (federal) · Source: “CMS Therapy Services guidance — CQ/CO modifiers for assistant-furnished services (established CY 2019; de minimis standard CY 2020)” · Last reviewed: 2026-10-08
Payer and authorization checks
Commercial payer therapy policies diverge from Medicare in the details that matter: some payers use per-code unit calculations (the “rule of eights”) instead of Medicare’s total-time methodology, visit limits and authorization requirements vary widely, and telehealth coverage for therapy has payer-specific rules. Billing a commercial claim with Medicare’s unit logic — or vice versa — produces systematic errors in one direction or the other. We verify each payer’s therapy policy during onboarding, confirm authorization requirements before the episode where required, and track visit authorizations against scheduled sessions. Our eligibility and prior authorization team manages the authorization volume.
Workflow and reporting
Therapy clinics need reporting built around visits and units. We provide visit-level reporting (units billed versus minutes documented, timed versus untimed mix, evaluation-to-treatment ratios), denial reporting by cause (unit errors, threshold denials, authorization failures, plan-of-care issues), and payer-level payment tracking that shows effective per-visit payment by payer. Reports arrive on a set schedule with every metric defined. Payment posting includes contractual adjustments per payer fee schedule, and denial management follows a documented path from correction to appeal.
Onboarding and pricing factors
Onboarding a physical therapy practice starts with a unit audit: we recalculate billed units from documented minutes across a sample of visits and compare against what was actually claimed — this single check typically reveals whether the clinic is systematically under- or over-billing. We then review KX modifier usage, plan-of-care certification status, and assistant-modifier compliance, confirm we can work inside your existing EHR and practice-management systems with compatibility confirmed during onboarding, and set up daily claim submission. We do not publish flat rates: pricing is quoted and scoped in your written proposal after we review your visit volume, payer mix, and systems. Data is handled under our HIPAA safeguards and business associate agreement. No client outcomes are cited until verified and permissioned.
FAQs and dated sources
How does the 8-minute rule work?
Medicare assigns one billable unit per timed therapy code based on total treatment minutes: 8–22 minutes earns one unit, 23–37 two units, 38–52 three units, and 53–67 four units. When several timed services are furnished in one visit, units follow total time, with leftover minutes of 8 or more earning an extra unit for the longest service. Only direct one-on-one time counts. Source: Medicare Claims Processing Manual, Pub. 100-04, Chapter 5 — last reviewed 2026-10-08.
When is the KX modifier required?
The KX modifier is required on therapy claims once the beneficiary’s incurred therapy expenses for the year reach the annual threshold — it attests the services are reasonable and necessary with supporting documentation. Claims above the threshold without KX are denied. The threshold amount is updated annually by CMS, so tracking must use the current-year figure.
What is the difference between timed and untimed therapy codes?
Timed codes (such as therapeutic exercise 97110 or neuromuscular reeducation 97112) are billed in 15-minute units under the 8-minute rule. Untimed codes — including PT evaluations (97161–97163), reevaluation (97164), and hot/cold packs — are billed once per session regardless of minutes and are excluded from the timed-unit calculation.
Why do our therapy claims get denied for plan-of-care issues?
Medicare requires outpatient therapy to be furnished under a written plan of care that is certified by a physician or qualified nonphysician practitioner. Missing certification, an expired or unsigned plan, or treatment that does not match the certified plan all produce denials. We track certification status per patient during onboarding and ongoing.
Do commercial payers follow the 8-minute rule?
Not always. Some commercial payers calculate units per CPT code rather than by total treatment time, and authorization and visit-limit rules vary by plan. We confirm each payer’s therapy billing methodology during onboarding and apply the correct logic per claim.
How do you handle PTA-furnished services?
When a physical therapist assistant independently furnishes more than a de minimis portion of a service, the CQ modifier is reported alongside GP, and the payment reduction applies to that portion. We track therapist versus assistant minutes per the CMS standard so the modifiers — and the payment — are correct.
General educational information, not legal advice or a guarantee of reimbursement. Requirements vary by payer, plan, setting and date of service.
CPT is a registered trademark of the American Medical Association.
Medical Billing Services Group — Medical Billing & Revenue Cycle Management. Remote, serving all 50 US states. Call +1 (307) 396-4107 or email contact@medicalbillingservicesgroup.com — or contact our team to start with a Free Billing Audit.