therapy-billing-and-units

name	therapy-billing-and-units
description	Calculate PT/rehab billable units correctly: separate timed (time-based, 15-min) from untimed (service-based) CPT codes, apply the 8-minute rule to total timed units, and place GP/KX/59 modifiers — confirming the payor's rule variant before billing.

Therapy Billing & Units

Get the units right before anything else; the modifier and the claim ride on them.

Step 1 — timed vs untimed

• Untimed (service-based) codes bill one unit per session regardless of minutes (e.g. an evaluation, some modalities).
• Timed (time-based) codes bill in 15-minute units under the 8-minute rule.

Step 2 — the 8-minute rule (timed codes)

• A single timed service needs ≥ 8 minutes to bill 1 unit.
• Total all timed minutes, then map cumulative minutes to units by the bracket table:

Total timed minutes	Units [verify-at-use payor variant]
8–22	1
23–37	2
38–52	3
53–67	4
+15 min	+1

• Mixed timed codes: total minutes → total units, then allocate units to codes (largest-remainder logic). The payor variant (CMS cumulative vs the per-service "rule of eights" some commercials use) decides edge cases — confirm it.

Step 3 — modifiers

Modifier	When
GP	Service under a PT plan of care (OT → GO, SLP → GN)
KX	Above the Medicare therapy threshold, attesting documented medical necessity
59 / X{EPSU}	A genuinely distinct service against an NCCI edit — never to force a bypass

Verify-at-use

• The 8-minute-rule variant and NCCI/modifier edits differ by payor and change — confirm against the specific payor before billing. The threshold dollar figure is [ESTIMATE] until checked — see ../../knowledge/pt-clinic-reference-2026.md.

Traverse the 8-minute-rule tree in ../../knowledge/pt-clinic-decision-trees.md.