Physical therapy is billed in units of time, which makes it the easiest specialty to underbill and the easiest to get audited for overbilling. The 8-minute rule, the therapy threshold, the KX modifier, plan-of-care certification dates and a visit cap that varies per contract all interact, and a mistake in any one of them is invisible until the remittance arrives.
Our physical therapy billing services cover outpatient PT clinics, multi-site rehab groups and practices that also provide OT and speech. Clinics comparing physical therapy medical billing services, or shortlisting the best physical therapy billing services in their market, should ask any physical therapy billing company one question: how do you calculate units, and do you do it per payer? If you are still joining networks, start with physical therapy credentialing services.
The 8-minute rule
Where most PT revenue is quietly lost
Medicare and most payers following its rules pay timed codes in 15-minute units, calculated on the total timed minutes in the visit, not per code. A visit with 8 minutes of 97110 and 7 minutes of 97140 is 15 total timed minutes, which is one unit, billed under the code with the most minutes. Split them and you have billed two units you cannot support.
Commercial payers do not all follow the Medicare method. Some use a per-code rule instead, which produces a different unit count from the identical visit. We set the calculation per payer rather than applying one rule to everything.
| Total timed minutes | Units |
|---|---|
| 8 to 22 | 1 |
| 23 to 37 | 2 |
| 38 to 52 | 3 |
| 53 to 67 | 4 |
| 68 to 82 | 5 |
The codes
| CPT | Service | Type |
|---|---|---|
| 97161 to 97163 | PT evaluation, low / moderate / high complexity | Untimed |
| 97164 | PT re-evaluation | Untimed |
| 97110 | Therapeutic exercise | Timed, 15 min |
| 97112 | Neuromuscular re-education | Timed |
| 97116 | Gait training | Timed |
| 97140 | Manual therapy | Timed |
| 97530 | Therapeutic activities | Timed |
| 97535 | Self-care / home management training | Timed |
| 97010 / 97012 / 97014 | Hot/cold packs, traction, e-stim unattended | Untimed; 97010 is bundled by most payers |
Modifiers that matter
- GP services delivered under an outpatient physical therapy plan of care. Missing it is one of the most common flat denials in PT.
- KX attests that services above the annual therapy threshold are medically necessary. Applied too early it invites review; applied too late the claims above the threshold deny.
- 59 / XS / XU: separates services that would otherwise be bundled, most often 97140 with 97530.
- CQ / CO: services provided in whole or part by a PTA or OTA, required on Medicare claims and carrying a payment reduction.
Therapy threshold and targeted review
Medicare no longer applies a hard cap, but it does apply an annual threshold above which the KX modifier is required, and a second, higher threshold above which claims may be selected for targeted medical review. We track each patient's cumulative therapy dollars across the year, including therapy they received elsewhere, which is the part clinics cannot see, and apply KX at the right point rather than by default.
Plan of care and certification dates
PT claims need a plan of care certified by the referring provider, recertified at the required interval, with a progress note at the required visit count. A lapsed certification denies every claim after the lapse date, and the denial reason rarely says so plainly.
We track certification and recertification dates per patient and flag them before the visit, not after the denial.
Rehab, OT and speech under one roof
Most clinics we bill for are not PT only. Rehab medical billing services across a mixed practice mean tracking the therapy threshold across disciplines for the same patient, using GP, GO and GN modifiers correctly, and knowing which payer puts paediatric speech under a different benefit entirely.
- Occupational therapyoccupational therapy billing services
- Speech-language pathologyspeech therapy billing services
What we do every week
- Eligibility and benefit checks, including the visit cap and whether a network manager owns the benefit.
- Charge entry with the payer's own 8-minute calculation applied.
- Modifier scrubbing: GP, KX, CQ/CO and the X-modifiers.
- Authorization and visit tracking against the contract limit.
- Plan-of-care date tracking and recertification reminders.
- Denial management, including bundling and medical necessity appeals.
- Payment posting and underpayment checks against contracted rates.
- Aged AR recovery, including balances a previous biller abandoned.
- Monthly reporting on units per visit, denial reasons and days in AR.
Billing and credentialing together
- Joining networks?Physical therapy credentialing services Medicare private practice enrollment, ASH and Optum Physical Health.
- Chiropractic alongside?Chiropractic billing services the same network managers run both.
Physical therapy billing FAQs
How does the 8-minute rule actually work?
Add up all timed minutes in the visit, then divide into 15-minute units: 8 to 22 minutes is one unit, 23 to 37 is two, and so on. The units are then assigned to the codes with the most minutes. Some commercial payers use a per-code rule instead, which gives a different answer for the same visit.
Why are my claims denying for a missing modifier?
Usually GP. Outpatient PT services need the GP modifier to show they are under a physical therapy plan of care, and many payers reject the line outright without it.
When should KX be applied?
Once the patient passes the annual therapy threshold and the documentation supports continued medical necessity. Applying it to every claim from the start is a recognized audit trigger.
Do you bill for PTAs?
Yes. PTA services are billed under the supervising therapist with the CQ modifier on Medicare claims, which carries a payment reduction. Supervision requirements vary by state and payer, and we set them per contract.
Can you recover our old AR?
Usually, yes. PT AR is full of unit-count denials and lapsed certifications, both of which are appealable if you get to them inside the timely filing window. The sooner we look, the more of it is still live.
Talk to a physical therapy biller
Send us a month of visits and your aged AR. We will show you the units you are leaving on the table and the denials that are still appealable.
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