A therapist who treats a patient for 37 minutes on one timed service bills two units. At 38 minutes, the same service bills three. That single minute is why billers learn this rule early. What follows is 8-minute rule physical therapy billing explained with examples, drawn from the Medicare Claims Processing Manual (Pub. 100-04, chapter 5, section 20.2) and from payer and state documents that show where the rule stops applying.
What is the 8-minute rule?
The 8-minute rule is shorthand for the way Medicare converts minutes of direct, one-on-one treatment into units of timed CPT codes, each defined as 15 minutes. Section 20.2 never uses the nickname. Its subsection C is titled “Counting Minutes for Timed Codes in 15 Minute Units,” and its opening instruction is that a lone timed service under 8 minutes in a day is not billed.
The counting table sits inside the section on reporting service units by HCPCS code, a requirement that took effect for claims submitted on or after April 1, 1998, when institutional providers began reporting units by procedure code instead of revenue code. Chapter 5 governs Medicare Part B outpatient rehabilitation claims, so the same method applies to physical therapy and occupational therapy. CMS’s own example of a 60-minute occupational therapy session billed as four units of 97530 shows it.
CMS expects physical therapy minutes per unit to average 15 across a practice. A consistent pattern of billing fewer minutes per unit, the manual says, should be highlighted for review.
Timed and untimed CPT codes for physical therapy
Timed codes are defined per 15 minutes of direct contact. Common examples include 97110 (therapeutic exercise), 97112 (neuromuscular re-education), 97116 (gait training), 97140 (manual therapy), 97530 (therapeutic activities) and 97035 (ultrasound). Untimed codes bill one unit per day however long the service runs. Evaluations and re-evaluations (97161 to 97164 for PT, 97165 to 97168 for OT) belong to this group, and the table in section 20.2 limits each to one unit per day.
Untimed minutes stay out of the timed total, but they still go in the note. CMS asks for total treatment minutes, including time spent on untimed services, in addition to total timed minutes.
Medicare 8 minute rule chart and cheat sheet
Section 20.2 publishes the units table below. It runs on total timed minutes for the date of service and continues in 15-minute steps beyond two hours.
Units | Total timed minutes |
1 | 8 to 22 |
2 | 23 to 37 |
3 | 38 to 52 |
4 | 53 to 67 |
5 | 68 to 82 |
6 | 83 to 97 |
7 | 98 to 112 |
8 | 113 to 127 |
Reading the chart: 35 minutes, 38 minutes and 4 units
Thirty-five minutes of timed therapy falls in the 23 to 37 band, so 2 units are reported. Thirty-eight minutes moves into the next band and gives 3 units. Four units cover 53 through 67 minutes, so visits of 55 and 65 minutes bill the same. For a quick check, divide the total by 15 and add one unit if 8 or more minutes remain.
Calculating units by hand: an 8 minute rule calculator
Billing software automates the steps, but the logic is short enough to run on paper.
- Add the minutes for every timed code delivered that day.
- Find the total on the chart to get the unit limit.
- Give each code one unit per full 15 minutes it received.
- Assign any remaining units to the codes with the most leftover minutes.
When two codes tie on leftover minutes, as with CMS’s example of two 20-minute services, the clinician may choose either one.
Physical therapy billing examples
One timed code
Seven minutes of 97110 alone: no unit. Eight minutes: one unit. Thirty-seven minutes: two units. Thirty-eight: three.
Three timed codes and a leftover
A visit includes 22 minutes of therapeutic exercise (97110), 8 minutes of manual therapy (97140) and 5 minutes of ultrasound (97035). The 35 timed minutes support two units. Exercise earns one for its first 15 minutes and has 7 left over. Manual therapy’s 8 minutes beat that, so 97140 gets the second unit. The ultrasound counts toward the total but bills nothing. CMS’s four-code example (49 minutes, including 8 minutes of ultrasound) ends the same way.
Two short services pooled
Seven minutes of therapeutic activities (97530) plus 6 minutes of neuromuscular re-education (97112) total 13 minutes. Neither reaches 8 alone. Together they support one unit, reported under 97530 because it took longer.
Evaluation plus treatment
A visit combines a physical therapy evaluation (97162, one unit), 20 minutes of 97110 and 10 minutes of 97530. Only the 30 timed minutes enter the calculation, which supports two units: one for the full block of exercise, one for 97530, whose 10 leftover minutes exceed the 5 left on exercise. The evaluation’s minutes go into total treatment time instead.
Medicare 8 minute rule vs rule of 8s
The AMA’s CPT guidelines work differently. The codebook’s instructions on time say “a unit of time is attained when the mid-point is passed,” a line APTA quotes in a template letter for providers writing to Anthem. For a 15-minute code the midpoint is 7.5 minutes, and each code is judged on its own. Billers call this the rule of eights (WebPT used that label in a December 2021 comparison by Melissa Hughes) or the substantial portion methodology (MedBridge’s billing guide).
Run 11 minutes of 97530 and 9 minutes of 97112 through both methods. Medicare pools the 20 minutes and allows one unit. The midpoint method credits each code separately and allows two.
What insurances follow the 8 minute rule outside Medicare?
Medicare Part B does. Every other payer depends on its own policy. The Medicaid 8 minute rule is set state by state: Colorado’s Health First Colorado manual for physical and occupational therapy reproduces the CMS table and examples, then adds a ceiling of five PT units per day. Commercial plans divide between the CMS and AMA methods, and APTA’s coding guidance recommends billing consistently across payers while acknowledging that the two standards differ.
Policies can also blend them. APTA reported on September 24, 2025 that Anthem’s policy “Guidelines for Reporting Timed Units for Physical Medicine and Rehabilitation Services,” in force since December 11, 2024, required start and stop times for each code. After APTA’s May 2025 letter, Anthem revised it effective August 13, 2025, and therapists no longer record those times. APTA had also objected to wording that merged the CMS rule with the CPT midpoint rule, a hybrid it said existing billing systems cannot handle. Read the current policy before assuming either method.
What counts as treatment time
Can a physical therapist bill for documentation time?
Not under timed codes. Section 20.3 starts the clock when the therapist, or an assistant under supervision, is working directly with the patient, who should already be in the treatment area and ready to begin. Pre- and post-service work, waiting for equipment, rest periods and bathroom breaks fall outside the count. Colorado’s Medicaid manual says it outright: time spent on preparation, report writing, record keeping and claims processing is not reimbursable.
Two clinicians working with one patient at the same moment still produce one unit per 15 minutes; CMS’s example is a stroke patient in the parallel bars who needs a therapist and an assistant, or two therapists. When a physical therapist assistant furnishes any part of a service, Medicare requires the CQ modifier (CO for occupational therapy assistants), mandatory since January 1, 2020, and pays 85 percent of the usual amount for dates of service from January 1, 2022.
Payment per unit also drops after the first. Since April 1, 2013, Medicare pays 50 percent of the practice expense component for the second and later units or procedures a patient receives on the same day (section 10.7).
Documentation that supports the units
Medicare does not require minutes for each intervention in the treatment note (Medicare Benefit Policy Manual, Pub. 100-02, chapter 15, section 220.3B). The total timed minutes must still appear, so a claim for three units needs at least 38 timed minutes behind it. Colorado Medicaid asks for more: its manual states that time for each intervention belongs in the visit note, and that units billed must match the documented timed minutes.
Quick reference for daily billing
For 8-minute rule physical therapy billing, four thresholds do most of the work: 8, 23, 38 and 53 total timed minutes for one through four units. Add every timed minute for the date of service, find the band, give each code its full 15-minute blocks, and send leftover units to the codes with the largest remainders. Evaluations and other untimed codes bill one unit and stay out of the count. Outside Medicare Part B, confirm which method the payer applies, because a visit split 11 and 9 minutes between two codes bills one unit under CMS counting and two under the midpoint rule.