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Guide · Part B Therapy

The 8-Minute Rule

Outpatient therapy is billed in 15-minute units — but minutes don’t divide cleanly into units. The 8-minute rule is how Medicare turns treatment time into billable units, and it trips up more claims than almost anything else in Part B therapy.

In short

For timed therapy codes, you need at least 8 minutes of one-on-one treatment to bill a unit. Total all timed minutes, read the unit count off a fixed table (8–22 = 1, 23–37 = 2, and so on), then assign the units to codes — most-time code first. Untimed codes bill one unit regardless of time.

Timed vs. untimed codes

The rule only applies to timed (constant-attendance) codes — one-on-one treatment measured by the minute. Untimed (service-based) codes, like an evaluation, bill a single unit no matter how long they take, so their minutes never enter the timed total.

Timed codesa.k.a. constant-attendanceOne-on-one, billed by the minute.The 8-minute rule applies.e.g. therapeutic exercise, manualtherapy, gait trainingUntimed codesa.k.a. service-basedOne unit per session, no matterhow long they take.e.g. evaluations, re-evaluations,some modalities
The rule only governs timed codes. Untimed (service-based) codes bill one unit per session regardless of duration, so keep their minutes out of the timed total.

The units table

Each unit represents a 15-minute block, but Medicare rounds on an 8-minute point: once you’re 8 minutes into a new block, you earn that unit. The result is a fixed lookup from total timed minutes to units.

8 – 22 minof timed treatment123 – 37 minof timed treatment238 – 52 minof timed treatment353 – 67 minof timed treatment468 – 82 minof timed treatment583 – 97 minof timed treatment6Each unit is a 15-minute block; the remainder must reach 8 minutes to round up to the next unit.
Total your timed minutes and read off the units. Under 8 minutes of timed treatment is not billable at all; from there each 15-minute block adds a unit, with an 8-minute rounding point.

How to calculate units

The key move is to total all the timed minutes first, then convert to units — not to round each code separately, which would inflate the count. Once you have the total units, assign them to codes, giving units to the codes that got the most time.

Code A30 minCode B15 minCode C8 min53 min totaltable → 4 unitsCode A2 unitsCode B1 unitCode C1 unitTotal the timed minutes, get the units from the table, then assign them to codes — most-time code first.4 units to split: the 30-minute code takes 2, the others one each.
Units are decided by the combined timed total — not code by code. Here 30 + 15 + 8 = 53 minutes supports four units, which are then distributed starting with the code that got the most time.

The remainder rule

Because the floor applies to the total, leftover minutes behave a little surprisingly. A single timed service under 8 minutes is worth nothing on its own — but small remainders from several timed codes combine, and if they reach 8 minutes together, that’s another unit.

7 minutes, one code7 min0 unitsBelow 8 minutes of a single timedservice, nothing is billable.4 + 5 + 4 across codes4 m5 m4 m1 unitLeftover minutes from several timedcodes combine — 13 ≥ 8, so one unit.
The 8-minute floor is about the timed total, not each code in isolation. A lone 7-minute service earns nothing, but small remainders across codes add up — reaching 8 yields a unit, billed to the code with the most time.

Documentation

The minutes have to be real and recorded. Only direct, one-on-one treatment time counts — not setup, paperwork, or rest — and notes should support exact treatment time and medical necessity. Inflated or rounded-up time is a common audit finding.

Key takeaways

  • Applies to timed codes; untimed codes are one unit per session.
  • At least 8 minutes of timed treatment is needed for any unit.
  • 8–22 = 1, 23–37 = 2, 38–52 = 3, 53–67 = 4, and so on in 15-minute steps.
  • Total the minutes first, then assign units to the most-time codes.
  • Remainders combine across codes; a lone sub-8-minute service is not billable.

Try it on the tools

Billing Units →Visit Estimator →KX Threshold Tracker →MPPR Calculator →

Last reviewed May 2026. Educational overview only — verify against the current CMS therapy services guidance and the Medicare Benefit Policy Manual, Chapter 15, before billing.