Physical therapy billing aligned to timed units and authorizations.

Physical therapy billing is largely a minutes discipline. Miscount them and you either underbill every visit or overbill your way into an audit. The 8-minute rule is how Medicare and most plans expect treatment time to become billable units. A small systematic error across dozens of visits a day compounds before anyone notices.

Timed vs untimed codes and the 8-minute rule

Timed codes such as 97110 (therapeutic exercise), 97112 (neuromuscular reeducation), 97140 (manual therapy), and 97530 (therapeutic activities) are billed in 15-minute units. Under Medicare’s 8-minute rule, one unit requires at least 8 minutes of that service; total timed minutes across codes determine how many units you can support. Untimed codes (evaluations, certain once-per-day modalities) do not consume that minute pool the same way — mixing the logic is a common new-biller error.

If the therapist documents 20 minutes of 97110 and 20 minutes of 97140, that is not automatically four units. Total timed minutes and distribution across codes matter. We audit unit math weekly until the clinic’s error rate stays near zero.

GP modifier, therapy thresholds, and KX

Medicare outpatient therapy claims need the GP modifier for PT services (GO for OT, GN for SLP). When a patient approaches the annual therapy threshold, medically necessary services beyond the threshold require the KX modifier and documentation that supports continued skilled care. Skipping KX is an automatic denial. Applying KX without supporting notes invites audit.

• Calculate timed units from documented minutes, not from the number of exercises listed.
• Append GP on PT claims; confirm discipline modifiers when OT or SLP shares the chart.
• Track cumulative therapy dollars toward the threshold before the visit that crosses it.
• Attach KX only when the record supports medical necessity past the threshold.

Plan of care, certification, and re-evaluation

Medicare expects a plan of care certified by a physician or allowed practitioner, with recertification on the required cadence. Commercial authorization visit counts are a separate risk: treating past the authorized visit without an extension becomes a write-off. Progress notes must show skilled care and functional progress; cloned notes that change only the date create denial and compliance problems.

Authorization tracking that protects the schedule

High-volume PT clinics often lose more to expired authorizations than to exotic coding errors. Our physical therapy medical billing workflow counts visits against auth, flags the third-to-last visit, and holds claim submission for visits past the authorized count until clinical staff extends coverage or the patient is converted to self-pay with consent. Clean claims at 97%+ mean little if half the schedule was never authorized.

Evaluations (97161–97163 by complexity) and re-evaluations (97164) have frequency expectations. Rebilling a full evaluation after every care gap without meeting re-eval criteria creates denials. Supervisory rules for assistants vary by payer and state — if the note cannot show who rendered skilled care, the unit will not hold. Get that right and A/R typically stays under 28 days without weekend catch-up.