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Guide

The 8-minute rule: how therapy units are counted

Both rules turn timed treatment minutes into 15-minute units, and both bill an extra unit once the remainder passes eight. They differ on one step: Medicare pools every timed minute in the visit before dividing, while the AMA rule of eights divides each service separately. Which one applies is set by the payer contract.

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The one-sentence version

Divide by fifteen first, then look at what is left over. If the remainder is eight minutes or more, it earns one more unit; if it is seven or fewer, it earns nothing.

That order matters and it is the thing most often asked backwards. The 15 comes first. Eight is not a starting threshold you clear before billing begins — it is the test applied to the remainder after the whole units have been taken out.

The two rules, and the single step that separates them

Both rules share the arithmetic above. They disagree about what goes into it.

Medicare’s 8-minute rule aggregates. Every timed minute in the visit pools into one total before the division runs. Forty minutes of treatment is two whole units with a ten-minute remainder, and because ten is at least eight, the visit bills three units — regardless of how those forty minutes were split across codes.

The AMA rule of eights never aggregates. Each timed service is divided on its own minutes, with the same fifteen-and-remainder arithmetic applied independently. It is also called the midpoint rule, because a service bills a unit once its minutes pass the midpoint of that unit.

The divergence is not academic. Three timed services of ten minutes each:

Medicare’s aggregate ruleAMA rule of eights
Service A — 10 min1 unit
Service B — 10 min1 unit
Service C — 10 min1 unit
Total30 min → 2 units3 units

The same visit, documented identically, bills a third more under one rule than the other. Nothing about the treatment changed — only which contract it was billed under.

Which rule applies to a given claim

It follows the payer contract, and it is not a property of the discipline, the setting or the patient. Physical, occupational and speech therapy all bill under whichever rule the contract specifies, and a practice with fifteen payer contracts may be running both rules on the same afternoon.

Two consequences follow, and they are the practical ones:

  • A rule cannot be set globally. Software that hard-codes one convention misbills under the other silently — the claim looks clean, it is simply worth less than the visit earned, and it never bounces back to tell you.
  • It has to be confirmed contract by contract. Some commercial payers adopt Medicare’s aggregate approach, others the AMA per-service approach, and the same insurer can differ across its plans.

In MegAligna the rule is a per-payer setting, the minutes come from the daily note, and the units land on the charge without anyone re-deriving them. That is the whole argument for computing units from documentation rather than from a spreadsheet at the end of the week — see charge capture.

What does not go into the timed total

Untimed codes never enter the minute pool. Evaluations, re-evaluations and unattended modalities bill one unit regardless of how long they took, and adding their minutes to the timed total is the most common spreadsheet error in the whole exercise. It inflates units, it is invisible at the time, and it is the kind of pattern a payer audit finds in bulk.

Occupational therapy has a sharper version of this problem than most, because OT evaluations carry complexity tiers that a duration-based rule would happily mangle — see OT billing.

Documentation time, set-up time and time the patient spent unattended are not treatment minutes either. What counts is the time the clinician was delivering the timed service.

Where the units end up on the claim

Whichever rule produced them, the number lands in Box 24G of the CMS-1500, on the line for that service. A unit count that disagrees with the minutes in the note is the single easiest thing for a payer to find on audit, because both numbers are in the record and one of them is arithmetic.

The CMS-1500 field guide covers 24G alongside the other boxes that decide whether a technically complete claim gets paid.

Four errors that cost units

  1. Testing the remainder before dividing. Eight is the remainder test, not an entry threshold. A 22-minute service is one unit plus a 7-minute remainder, which earns nothing — not two.
  2. Pooling minutes under a contract that does not pool. Aggregating under a rule-of-eights contract systematically under-bills multi-service visits.
  3. Counting untimed codes into the total. Inflates units and reads as a pattern rather than an error.
  4. Re-deriving units by hand at billing time. Checking one visit is quick. Checking thirty a day is where transcription errors enter, and they enter in the direction of whoever is tired.

Run a visit through the units calculator to see both rules side by side.

Common questions

What comes first, the 8 minutes or the 15?
The 15. Divide the timed minutes into whole 15-minute units first, then test what is left over against 8. Eight minutes is the remainder threshold that earns one additional unit — it is not a minimum you must reach before billing anything.
Is the rule of eights the same as the midpoint rule?
Yes. The AMA rule of eights is commonly called the midpoint rule, because each timed service earns a unit once its own minutes pass the midpoint of that unit. The defining feature is that it never pools minutes across services the way Medicare aggregates them.
Why is 8 minutes the threshold?
Eight is the midpoint of a 15-minute unit, rounded up. Both rules descend from the same idea — bill a unit once you pass its midpoint — and diverge only on whether minutes pool across services before the arithmetic runs.
Does the 8-minute rule apply to occupational therapy?
It applies to timed occupational therapy codes wherever the payer contract specifies Medicare's aggregate rule, exactly as it does for physical and speech therapy. The rule follows the contract, not the discipline, so the same OT department can bill under both rules across different payers.
Do untimed codes count toward the minutes?
No. Untimed codes — evaluations, unattended modalities — bill one unit regardless of duration and never enter the timed-minute total. Mixing them in is a common spreadsheet error that inflates units.
Which rule do commercial payers follow?
It is contract-specific. Some commercial payers adopt Medicare's aggregate rule, others the AMA per-service rule, and the same insurer can differ by plan. The only defensible practice is confirming per contract and configuring per payer.

Try it end to end with test data

14 days, no card required. Use made-up patients while you evaluate — real patient information waits until a business associate agreement is in place.

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