Physical therapy billing and the 8-minute rule in 2026

The 8-minute rule is Medicare’s method for converting timed therapy minutes into billable 15-minute units. You need at least 8 minutes of a timed service to bill one unit. Medicare requires you to total all timed minutes in the session first, then map that total to the unit table. CMS made no changes to the methodology for 2026, but the KX modifier threshold rose to $2,480.

Therapy billing runs on rules no other specialty uses, and the single most expensive misunderstanding is not the 8-minute threshold itself. It is how leftover minutes are handled, and whether the payer in front of you uses Medicare’s method or the AMA’s.

The unit table

Total timed minutes	Billable units
8 to 22	1
23 to 37	2
38 to 52	3
53 to 67	4
68 to 82	5

Timed codes, also called constant attendance codes, require ongoing one-on-one interaction and are billed in 15-minute increments. The common ones are 97110 therapeutic exercise, 97112 neuromuscular re-education, 97140 manual therapy, and 97530 therapeutic activities. Untimed codes are billed once per session regardless of duration, including evaluations 97161 to 97163 and modalities such as 97010 hot and cold packs.

The part that costs money: pooling leftover minutes

Medicare’s methodology, set out in the Claims Processing Manual, requires you to add all timed minutes together first and then determine total units from the table. Leftover minutes from different codes are pooled, and if the pooled remainder reaches 8 minutes it generates an additional unit, which goes to the code with the most remaining time.

A worked example makes it concrete. A session includes 33 minutes of 97110 and 7 minutes of 97140, totalling 40 timed minutes, which maps to 3 units. 97110 accounts for 2 full units at 30 minutes, leaving 3 minutes. 97140 has 7 minutes. The pooled remainder is 10 minutes, which exceeds 8 and generates the third unit. That unit goes to 97140, because 7 exceeds 3. Final allocation: 97110 gets 2 units, 97140 gets 1.

Billed code by code in isolation, 97140 at 7 minutes would have been dropped entirely and the session would have paid 2 units. Clinics that calculate per code rather than pooling are systematically underbilling, one unit at a time, on a large share of mixed-code sessions.

Here is the complication. Many commercial payers do not use Medicare’s method. They apply the AMA’s Rule of Eights, also called the Substantial Portion Methodology, which evaluates each code separately and requires 8 minutes of that specific service. Under that standard the 7 minutes of 97140 above is not billable. Applying one method universally guarantees you are wrong with roughly half your payer mix, in one direction or the other. This is a payer-specific rule that belongs in your claim scrubbing edit library, not in a therapist’s memory.

The 2026 thresholds

The methodology did not change for 2026. The dollar thresholds around it did.

• KX modifier threshold: $2,480 for 2026, up from $2,330. Once a patient’s cumulative allowed charges for physical therapy and speech-language pathology combined cross that figure, every subsequent claim line needs the KX modifier or Medicare denies it outright. Occupational therapy carries its own separate $2,480 threshold.
• Targeted medical review threshold: $3,000 for PT and SLP combined, with a separate $3,000 for OT, fixed through 2028. Above this level documentation should be treated as audit-ready by default.

The KX modifier is a clinical attestation, not a billing formality. Appending it certifies that services above the threshold are medically necessary and that the documentation supports that conclusion. Clinics that apply KX automatically without confirming the documentation are creating exposure across every KX-modified claim in the period, not just the weak ones. Tracking cumulative spend per patient, with an alert before the threshold rather than after, needs a named process owner.

The modifiers that decide payment

• GP: services delivered under a physical therapy plan of care. Discipline-specific and required.
• KX: above the annual threshold, with documentation supporting necessity.
• CQ: services furnished in whole or substantial part by a physical therapist assistant, which carries a payment differential. Verify your documentation actually supports the CQ determinations you are making.
• 59 or the X-series: for genuinely distinct services on the same date that would otherwise bundle. 97110 with 97140 is the most commonly affected pair in physical therapy, and billing both without the modifier on the correct code invites the payer to bundle one into the other and reduce payment.
• 95: telehealth for commercial payers, with POS 10 for Medicare telehealth where the patient is at home. Medicare telehealth coverage for therapy is limited: evaluations and therapeutic exercise via real-time audio-video are covered, while modalities and hands-on manual therapy are not.

One perennial trap worth naming: billing 97014 for electrical stimulation on a Medicare claim instead of G0283. The denial that produces often surfaces weeks later in the aging report rather than immediately, which is precisely why it recurs.

Documentation that survives review

Time allocation is the failure that matters most. A note recording a 50-minute session with 97110, 97140, and 97530 and no per-code minute breakdown cannot support any unit calculation, and a reviewer will treat the whole session as unsupported. Record minutes per code, every session.

Beyond time, the note should answer what a reviewer will ask: what specific intervention, at what intensity, why that intervention, how the patient responded, and what clinical decision followed. That takes an extra minute to write and is the difference between a claim that pays and one that does not. Plan of care certification and recertification dates need systematic tracking with alerts before expiry, because an expired certification invalidates otherwise clean claims.

For orthopedic and rehabilitation practices wanting this run properly across payers, that operational layer is orthopedic medical billing services, with unworked therapy denials handled through denial management and aged balances through accounts receivable follow-up. To find out how many units you are leaving behind, start with a free instant revenue audit.

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