An orthopedic group we work with hired its first physical therapist in the spring. The surgeons were pleased: post-op patients stayed in the building, and the schedule filled in three weeks. The billing office was less pleased. Within two months they had denials for missing GP modifiers, a Medicare letter about a plan of care that no physician had signed, a stack of claims over the therapy threshold with no KX modifier, and a therapist who was billing four units for a 40-minute visit because "that is how the clinic I came from did it."
Physical therapy billing in a physician practice is a different discipline from billing the physicians. The codes are mostly timed, the units are counted by a rule that only exists in Medicare's manuals, the payment depends on an annual dollar threshold, and the whole thing rests on a plan of care that has to be certified by a physician on a schedule. None of that is hard once it is written down. Almost none of it is written down in the practices that add therapy.
A glossary line. A timed code is a CPT code defined as "each 15 minutes," so the number of units depends on how long the therapist spent. An untimed code is billed once per session regardless of time. The plan of care is the written treatment plan the therapist creates at the evaluation, which Medicare requires a physician or non-physician practitioner to certify.
Key takeaways
- Under Medicare's 8-minute rule, total the minutes of all timed codes in the session, then convert to units: 8 to 22 minutes is one unit, 23 to 37 is two, 38 to 52 is three, 53 to 67 is four.
- The 2026 KX modifier threshold is $2,480 for physical therapy and speech-language pathology combined; every therapy line after the patient crosses it needs the KX modifier or it denies.
- The plan of care must be certified by a physician or NPP within 30 days of the initial treatment and recertified at least every 90 days.
- Services furnished in whole or in part by a physical therapist assistant carry the CQ modifier and pay at 85 percent of the fee schedule.
- Every physical therapy line to Medicare carries the GP modifier; a missing GP is the most common and most avoidable denial.
The 8-minute rule for physical therapy billing in a physician practice
Medicare pays timed therapy codes in 15-minute units, and the 8-minute rule decides how many units a session supports. The method is to add the minutes of every timed code in the session, then look up the total in the table. A unit is earned for every full 15 minutes, plus one more unit if the remainder is at least 8 minutes. Untimed codes (the evaluation codes 97161 to 97163, re-evaluation 97164, unattended electrical stimulation G0283, mechanical traction 97012) are billed once and their minutes stay out of the total. Hot and cold packs, 97010, are bundled by Medicare and not paid separately at all.
| Total timed minutes | Units billable |
|---|---|
| 8 to 22 | 1 |
| 23 to 37 | 2 |
| 38 to 52 | 3 |
| 53 to 67 | 4 |
| 68 to 82 | 5 |
Here is where the therapist from the other clinic went wrong. A session with 23 minutes of therapeutic exercise (97110), 12 minutes of manual therapy (97140) and 10 minutes of hot packs has 35 timed minutes. Under the 8-minute rule that is two units total, not three, and the hot pack is not billed. The therapist assigns the two units to the codes with the most minutes: one unit of 97110 and one of 97140. The AMA's CPT method counts differently, code by code, so that 23 minutes of 97110 alone supports two units and the 12 minutes of 97140 a third; some commercial payers follow that method, and the practice needs to know which payers do. The therapist's note has to record the minutes for each timed code and the total treatment time, because that is exactly what an auditor recalculates.
The KX modifier threshold and the $3,000 review line
Medicare no longer has a hard therapy cap, but it has a threshold that behaves like one for billing purposes. For 2026 the KX modifier threshold is $2,480 for physical therapy and speech-language pathology services combined, and a separate $2,480 for occupational therapy. The amounts count what Medicare allowed, including the patient's deductible and coinsurance, across every provider the patient saw that calendar year, not just yours. Once a patient's year-to-date therapy passes the threshold, each further therapy line needs the KX modifier, which is the therapist's attestation that the services remain medically necessary and that the record supports it. A line over the threshold without KX denies automatically. There is no appeal that fixes a missing modifier; you correct and resubmit.
A second line sits at $3,000. Claims above it are subject to targeted medical review, which does not mean every claim is reviewed; it means the contractor selects providers with unusual patterns, such as high units per visit or a high percentage of patients over the threshold. A physician practice with one therapist who treats mostly post-surgical patients will cross $2,480 with some patients and $3,000 with a few. That is normal. What matters is that the record for those patients shows progress toward the goals in the plan of care and a reason the patient still needs skilled care.
Operationally, the practice needs a way to know each Medicare patient's year-to-date therapy dollars. The MAC portal shows the accrued amount, and the therapist should check it at the evaluation and whenever the practice's own total approaches $2,000, because the patient may have had therapy elsewhere earlier in the year. A patient who arrives in September with $2,300 already accrued needs KX on the second visit.
Plan of care certification: the 30 and 90 day clocks
Medicare pays outpatient therapy only under a plan of care that a physician or non-physician practitioner has certified. The therapist writes the plan at the evaluation. It has to contain the diagnoses, the long-term treatment goals, and the type, amount, duration and frequency of the therapy (for example, "therapeutic exercise, manual therapy and gait training, three times a week for eight weeks"). The certification is the physician's dated signature on that plan, or on a document that references it, and it has to happen within 30 days of the first treatment day. If it is late, Medicare allows a delayed certification with a stated reason, but auditors read a pattern of late certifications as a program without a process.
Recertification is due at least every 90 days, or sooner if the plan changes significantly. In a physician practice this should be the easy part, because the certifying physician is down the hall. It fails anyway, usually because nobody owns it. The fix is a report of active therapy patients with the initial certification date and the next recertification due date, reviewed weekly, and a rule that the physician signs at the same visit where they see the patient for follow-up. When a patient is referred by an outside physician, the practice's own physician can still certify, but only if they are actually involved in the patient's care; a signature from a physician who has never seen the patient is not a certification.
Modifiers: GP, CQ and the therapy reduction
Every physical therapy service billed to Medicare carries the GP modifier, which identifies it as furnished under a physical therapy plan of care. Occupational therapy uses GO and speech-language pathology uses GN. Medicare's system requires the therapy modifier on codes it classifies as "always therapy," and a claim without it denies. The scrubber rule is simple: rendering provider is a PT, code is a therapy code, GP is present.
The CQ modifier goes on any unit furnished in whole or in part by a physical therapist assistant, and since January 1, 2022 those units pay at 85 percent of the fee schedule amount. "In part" has a de minimis standard: if the PTA furnished more than 10 percent of the minutes of a unit, the unit carries CQ. When a PT and a PTA both treat during one session, the minutes are split and the units assigned accordingly, and the note has to show who did what. Practices that hire a PTA to extend a therapist's capacity should build the 15 percent reduction into the staffing math before they hire.
The multiple procedure payment reduction applies to therapy too. When more than one "always therapy" code is billed for the same patient on the same day, Medicare pays the practice expense portion of the second and subsequent codes at 50 percent. The reduction is automatic; nothing on the claim triggers or prevents it. It does mean that a three-unit session does not pay three times a one-unit session, which matters when a practice projects therapy revenue from a fee schedule lookup.
| Modifier | When it goes on the line | Payment effect |
|---|---|---|
| GP | Every service under a PT plan of care | None; required for payment |
| KX | Every therapy line after the patient exceeds $2,480 in 2026 | Allows payment above the threshold |
| CQ | Units furnished in whole or in part (more than 10 percent) by a PTA | Paid at 85 percent |
| 59 or X modifiers | Only when an NCCI edit pairs two codes that were genuinely distinct | Bypasses the edit; needs documentation |
Who bills: the therapist's enrollment decision
This is the choice practices make by default and regret. A physical therapist in a physician practice can be enrolled in Medicare as a physical therapist in private practice, reassigning benefits to the group, and bill as the rendering provider on the claim. Or the practice can bill therapy incident to the physician, under the physician's NPI. Medicare allows the second route only if the therapy is furnished by someone who meets the qualifications of a licensed therapist and all the incident-to conditions are met, including the physician's direct supervision in the office suite. In practice that means the incident-to route saves nothing (the therapist still has to be a therapist) and adds a supervision requirement that fails the moment the physician is in surgery. We think nearly every physician practice should enroll the therapist and bill under the therapist's NPI, with the GP modifier and the certified plan of care. Our enrollment team handles this as an individual Medicare enrollment with reassignment to the group, plus the commercial payer credentialing, which for therapists often runs on a separate network from the physicians.
Commercial payers add their own layers: visit limits per year, authorization after a set number of visits, and different rules on the 8-minute method. Track visit counts per patient per payer from the first visit, and put the authorization trigger in the schedule, not in the therapist's head.
Questions we hear
Can the therapist bill an evaluation and treatment on the same day?
Yes, when the treatment is documented separately and the plan of care supports it. The evaluation code is untimed and its minutes stay out of the 8-minute total; only the timed treatment minutes count toward units.
Our physician signs the plan of care but the referral came from an outside orthopedist. Is that all right?
Medicare requires the certifying physician to be involved in the patient's care, which can be as the referring physician or as a physician who has seen the patient and agrees with the plan. A signature with no involvement is not a certification, and auditors ask to see the visit.
Do commercial payers use the KX modifier?
Generally not. KX is a Medicare requirement tied to the Medicare threshold. Commercial plans manage therapy with visit limits and authorizations instead, and Medicare Advantage plans may do either; check each plan's policy.
What to do this week
- Pull every therapy claim from the last 90 days and check for the GP modifier, the KX modifier where the patient is over $2,480, and the CQ modifier where a PTA treated.
- Build the active-therapy-patient report with certification and recertification dates, and assign one person to review it weekly.
- Have the therapist recount units on twenty recent notes using the 8-minute table and compare with what was billed.
- Check the year-to-date therapy dollars on the MAC portal for every active Medicare therapy patient.
- Confirm how the therapist is enrolled with Medicare and each major commercial payer, and start the individual enrollment if therapy is being billed incident to the physicians.
