Medicare’s 8-minute rule determines how many billable units of time-based CPT codes a physical therapy practice can report for a single date of service. In short: you total the minutes spent on all time-based services, and you may bill one unit for each full 15 minutes, plus one additional unit if at least 8 minutes remain. Getting this calculation wrong in either direction means lost revenue or audit exposure, so it is one of the first things we check when a PT practice asks us to review its billing.
What Is the 8-Minute Rule?
Many outpatient therapy CPT codes are defined in 15-minute increments. Because real treatment sessions rarely break into neat 15-minute blocks, Medicare uses the 8-minute rule to decide when a partial increment counts as a billable unit. The threshold is simple: a leftover block of time counts as a unit only if it lasts at least 8 minutes. Seven minutes of a timed service, by itself, is not billable to Medicare; eight minutes is.
The rule applies to services billed to Medicare Part B and to many Medicaid programs and commercial payers that follow Medicare’s methodology. Some commercial payers instead follow the AMA’s approach, which evaluates each timed code on its own rather than pooling minutes — one of several reasons specialty-aware medical billing services matter for therapy practices with a mixed payer list.
Timed vs. Untimed Codes: Why the Distinction Matters
The 8-minute rule only applies to time-based (timed) codes — services defined in 15-minute units where the clinician provides direct, one-on-one care. Common examples in physical therapy include:
- 97110 — therapeutic exercise
- 97112 — neuromuscular re-education
- 97116 — gait training
- 97140 — manual therapy
- 97530 — therapeutic activities
Untimed (service-based) codes are billed once per session regardless of how long they take. Examples include the physical therapy evaluation codes (97161–97163) and supervised modalities such as hot/cold packs (97010) and unattended electrical stimulation. Untimed codes never enter the 8-minute-rule math. A frequent documentation error is lumping untimed-service minutes into the timed total, which inflates units and creates overpayment risk.
How Do You Calculate Billable Units?
Under Medicare’s method, you add up the total minutes of all timed services for the visit, then apply the unit thresholds below.
| Total timed minutes | Billable units |
|---|---|
| 8–22 minutes | 1 unit |
| 23–37 minutes | 2 units |
| 38–52 minutes | 3 units |
| 53–67 minutes | 4 units |
| 68–82 minutes | 5 units |
| 83–97 minutes | 6 units |
The pattern continues in 15-minute steps. A quick check: divide total timed minutes by 15; each whole quotient is a unit, and a remainder of 8 or more adds one final unit.
A Worked Example
A patient receives 25 minutes of therapeutic exercise (97110), 15 minutes of manual therapy (97140), and unattended electrical stimulation (untimed).
- Total the timed minutes: 25 + 15 = 40. The untimed modality is excluded and billed once on its own.
- 40 minutes falls in the 38–52 range, so 3 units of timed codes are billable.
- Assign units by service: 97110 gets 1 full 15-minute unit with 10 minutes remaining; 97140 gets 1 full unit with 0 remaining. That accounts for 2 units.
- The third unit goes to the service with the most leftover minutes — 97110’s 10 remaining minutes beat 97140’s 0 — so the claim shows 2 units of 97110 and 1 unit of 97140, plus the untimed modality.
What About Mixed Remainders?
Mixed-remainder scenarios are where most under- and over-billing happens. Suppose a session includes 20 minutes of 97110 and 12 minutes of 97530. The total is 32 minutes — 2 units. Each code has one “extra” chunk (5 minutes and 12 minutes beyond a single unit’s worth of assignment), but only two total units are allowed. The correct approach is to bill 1 unit of each code, because the pooled total governs the unit count, and remaining minutes are assigned to the services with the largest remainders. Billing 2 units of 97110 plus 1 of 97530 here would overstate the visit.
The reverse mistake is just as common: therapists who evaluate each code in isolation may drop billable time. Suppose a visit includes 7 minutes of 97110 and 5 minutes of 97140. Neither service reaches 8 minutes on its own, so a code-by-code reading yields zero units — but under Medicare’s method the minutes pool to a 12-minute total, which supports 1 unit, billed for the service with the most minutes (here, 97110). This pooling-versus-per-code split is exactly the difference between Medicare’s method and the AMA-style approach some commercial plans use, and it is why your billing team must know which payer follows which rule.
Documentation That Supports Your Units
Minutes drive units, so minutes must be in the record. Best practice is to document total treatment time and total timed-code time for every visit, along with the minutes attributable to each timed service. If a Medicare reviewer cannot reconstruct your unit math from the note, the units are at risk in an audit — even when the care itself was appropriate. Consistent flowsheet templates and a brief end-of-visit time summary solve most of this.
If your denial reports show unit-count mismatches, downcoded visits, or payer-specific edits you cannot explain, a free billing consultation is a low-effort way to find out how much revenue the math is costing you. AMS Solutions has worked with time-based billing since 1992, and our team reviews payer-by-payer unit methodology as part of every therapy billing engagement.
Frequently Asked Questions
Does the 8-minute rule apply to all insurance payers?
No. It is Medicare’s methodology, and many Medicaid and commercial plans adopt it, but some commercial payers follow the AMA’s per-code approach instead. Always confirm each payer’s policy in writing rather than assuming Medicare rules apply everywhere.
Can I bill a timed code for 7 minutes of treatment?
Not to Medicare on its own — a leftover block must reach 8 minutes to count as a unit. However, those minutes still pool into the day’s total timed minutes, so they are not necessarily wasted; they may push the total over the next unit threshold.
Do evaluation codes count toward the 8-minute rule?
No. Physical therapy evaluations (97161–97163) are untimed, service-based codes billed once per session. Only time-based codes defined in 15-minute increments enter the unit calculation.
What happens if my documented minutes don’t support the units billed?
Payers can deny or downcode the claim, and in post-payment review they can recoup payments. Documenting per-service minutes and total timed minutes on every note is the most reliable protection.
