The 8-Minute Rule for Physical Therapy Billing: Chart, Calculator Steps and Worked Examples

Updated 2026-10-23. Reviewed by Jacob Greenberg, ClaimCarePro.

The 8-minute rule is Medicare's method for billing timed physical therapy codes: you add up the minutes of every timed service in the visit, then bill one 15-minute unit for 8 to 22 minutes, two units for 23 to 37, three for 38 to 52, and one more unit for each additional 15 minutes. A single service under 8 minutes is not billed.

That sentence covers most visits. The rest of this guide covers the parts that cause overbilling and underbilling: the full minutes-to-units chart, how to split the units between codes, how the CMS rule differs from the AMA's “rule of eights”, which payers use which, untimed codes, eight worked examples, what the note has to show, and the denials that follow when it goes wrong. Every rule below is taken from the CMS manuals and cited. If you want the billing done for you, see our physical therapy billing services.

8-minute rule chart: minutes to units

This is the CMS chart from the Medicare Claims Processing Manual, chapter 5, section 20.2 (Pub. 100-04, ch. 5, read 2026-10-23). Read the row that contains your total timed minutes for the day. The result is the most timed units you can bill on that date.

*CMS publishes rows for 1 through 8 units and states that “the pattern remains the same for treatment times in excess of 2 hours.” Rows 9 and 10 apply that pattern.

CMS also notes that the chart only helps you round minutes into units. It does not mean the first seven minutes of any service are dropped from the count. Every minute of direct timed treatment goes into the total.

What the CMS 8-minute rule actually says

The CMS 8-minute rule is five rules, not one. All five come from the same section of the Claims Processing Manual, and most billing errors come from skipping one of them.

1. Untimed codes are always one unit. When a code is not defined by time, you bill 1 unit no matter how many minutes it took.
2. Timed codes are 15-minute units, and a single service under 8 minutes is not billed. Codes such as 97110 and 97140 describe 15 minutes of direct, one-on-one contact.
3. The total sets the ceiling. When more than one timed code is performed on the same day, the total timed minutes decide how many units you can bill. You may not bill 4 units for less than 53 minutes, however many services were performed.
4. Fifteen minutes earns a unit. If a service ran at least 15 minutes, it gets at least one unit; 30 minutes or more, at least two. You cannot pour all of the day's minutes into one code if another service ran more than 15 minutes.
5. Short services can combine. If two or more timed services each ran 7 minutes or less and together total 8 minutes or more, bill one unit of the service that took the longest.

CMS adds a warning that matters on review: the work values for these codes assume an average of 15 minutes of direct contact per unit, and a provider who consistently bills units at less than 15 minutes each “should be highlighted for review.” The rule lets you round; it does not make 8 minutes the normal length of a unit.

8-minute rule calculator: four steps

You do not need an app to calculate units. These four steps reproduce the CMS logic for any visit:

1. Total the timed minutes. Add the minutes of every timed code delivered one-on-one. Leave out untimed codes (evaluations, unattended modalities) and non-billable time such as rest breaks.
2. Find the maximum units. Look the total up on the chart above.
3. Give each code its full units. Every full 15 minutes of a code is one unit of that code. Write down what is left over for each code.
4. Assign the remaining units by leftover minutes. If the chart allows more units than step 3 used, give the next unit to the code with the most leftover minutes, then the next, until you reach the maximum. If step 3 already used more units than the chart allows, drop units from the code with the fewest minutes.

Step 4 is the “mixed remainder” problem, and it is where most unit errors happen. Example 3 below is the CMS illustration of it.

8-minute rule examples (CMS method)

Examples 1 to 5 are the five worked examples CMS publishes in section 20.2, in plain language. Examples 6 to 8 apply the same rules to situations clinics ask about.

How each one works:

• Example 1. 47 minutes allows 3 units. Both codes ran more than 15 minutes, so each gets at least one. The third unit goes to 97112 because it took longer.
• Example 2. Tied minutes, so you pick which code gets the second unit. Billing 3 units of one code would ignore that the other ran over 15 minutes.
• Example 3, the mixed remainder. The first 30 minutes of 97110 are two full units. Compare what is left of 97110 (33 − 30 = 3 minutes) with the 7 minutes of 97140, and bill the larger: 97140. A code that ran only 7 minutes still gets billed, because the total allows a third unit and its 7 minutes beat the 3 leftover.
• Example 4. Four services, but 49 minutes allows only 3 units, so the three longest services are billed. You still record the ultrasound in the note; CMS requires every timed service to be documented, billed or not.
• Example 5. No single service reached 8 minutes, but together they reach 21, which is one unit. The therapist picks one code, since all three ran the same time.
• Example 6. One service, under 8 minutes, nothing else timed that day: no unit. If an untimed service was also done, that code is still billed.
• Example 7. The CMS manual's own example: 60 minutes of 97530 is 4 units.
• Example 8. The evaluation is an untimed code, one unit per day. Its minutes are left out of the timed total, so the 25 minutes of exercise alone set the timed units.

8-minute rule vs. the rule of eights (AMA CPT midpoint rule)

The difference is whether minutes are pooled. The CMS 8-minute rule adds the minutes of all timed codes together and sets the unit count from the total. The CPT time rule published by the AMA, which billers call the rule of eights or the midpoint rule, looks at each code on its own: “A unit of time is attained when the midpoint is passed,” so a 15-minute code earns its first unit at 8 minutes, its second at 23, and so on, and minutes from different codes are never combined. APTA describes the midpoint as 7 minutes 30 seconds for a 15-minute unit and notes that CPT does not require you to total the minutes (APTA, Coding for Timed Codes, read 2026-10-23).

The same visits, counted both ways:

Neither method always pays more. Pooling helps when there are many short services; counting per code helps when several services each run just past 8 minutes. Billing every payer by one method means some claims are overbilled and others underbilled.

Which payers follow the CMS 8-minute rule?

Medicare Part B requires the CMS method. Beyond that, the method is set by each payer's own policy and contract, not by a general rule:

• Commercial plans publish their own policies. Some follow CMS. Others publish the CPT method; Premera Blue Cross, for example, told providers that “a unit of time is attained when the midpoint is passed” and that the midpoint for a 15-minute code is 8 minutes (Premera provider news, November 7, 2019).
• Medicare Advantage, Medicaid and workers' compensation set their rules in their provider manuals, state fee schedules and contracts. Read the current manual for each plan rather than assuming it copies Medicare.
• The contract wins. APTA notes that if a payer contract sets a different threshold, the contract takes precedence over both the CMS and CPT standards.

In practice: keep a one-line note per payer in your billing system saying which method it uses and where that is written, and have your billing software apply it per payer. When a payer's manual is silent, ask the provider rep in writing and keep the answer.

Timed vs. untimed physical therapy codes

The 8-minute rule only applies to codes defined in 15-minute increments. Untimed codes are one unit per day, and their minutes stay out of the timed total.

Evaluation complexity is chosen from the documented history, examination, clinical presentation and decision making, not from minutes. The CPT descriptors list typical face-to-face times of 20 minutes (97161, low), 30 minutes (97162, moderate) and 45 minutes (97163, high), and 20 minutes for the 97164 re-evaluation (CMS MLN Matters MM9782). The level breakdown is on our physical therapy billing page.

Documentation requirements for timed codes

Medicare's Benefit Policy Manual, chapter 15, section 220.3, lists what every treatment note must contain (Pub. 100-02, ch. 15, read 2026-10-23):

• The date of treatment.
• Each intervention or modality provided and billed, timed and untimed, in language that can be compared with the claim. Record every timed service, even one you do not bill, because unbilled timed services can change the unit split.
• Total timed code treatment minutes and total treatment time in minutes. Total treatment time includes timed and untimed treatment but not non-billable time such as rest periods.
• The signature and professional identification of the qualified professional who furnished or supervised the services, and each person who contributed to the treatment.

CMS does not require minutes per intervention for Medicare, and contractors may not demand it. But the billed units and the total timed minutes must agree. Many clinics record minutes per code anyway: it is the only way to prove the unit split in examples 1 to 4 on review, and some commercial payers ask for time per code. If a physical therapist assistant furnished part of the visit, the note also has to show who did what, because Medicare pays services with the CQ modifier at 85% of the fee schedule amount once the assistant's share passes CMS's 10% de minimis standard (CMS Therapy Services).

For the rest of a defensible chart (plans of care, certifications, progress notes), see our guide to medical record documentation.

Common denials from 8-minute rule mistakes

Unit errors rarely deny as “8-minute rule”. They come back under general adjustment reason codes (X12 CARC list), which is why clinics miss the pattern.

For a wider look at why therapy claims come back unpaid, read why medical claims get denied.

Find the units you are missing

If you are not sure whether your units are right, send us 90 days of claims. Our free A/R audit shows the unit-count errors, the payers billed by the wrong method, the missing modifiers and the denials that can still be appealed. There is no obligation.

ClaimCarePro bills physical therapy at 6% of collections with a $1,000 monthly minimum, month-to-month, no setup fee. Aged and denied claims are worked on a 10% contingency: no recovery, no fee. See our physical therapy billing services or call (844) 772-8902, Monday to Friday, 9am to 5pm.

Frequently asked questions

Sources

• CMS Medicare Claims Processing Manual, Pub. 100-04, chapter 5, §20.2 (read 2026-10-23)
• CMS Medicare Benefit Policy Manual, Pub. 100-02, chapter 15, §220.3 (read 2026-10-23)
• CMS MLN Matters MM9782, PT and OT evaluation codes (read 2026-10-23)
• APTA, Coding for Timed Codes (read 2026-10-23)
• Premera Blue Cross, Billing for Time (November 7, 2019) (read 2026-10-23)
• X12 Claim Adjustment Reason Codes (read 2026-10-23)
• CMS Therapy Services (read 2026-10-16)