Physical therapy billing units are decided by minutes, not by codes: under Medicare's 8-minute rule the timed minutes of every timed code in the visit are added together and billed in 15-minute units, with a unit allowed once at least 8 minutes are documented, and untimed codes are one unit each regardless of time. Most small clinics count it right most of the time and lose a unit on the visits where two timed codes split the minutes. This page states the rule as CMS publishes it, works three visits through, separates the untimed codes, and lists the counting mistakes that cost a unit or invite an audit. The free billing units worksheet on this site does the arithmetic on any visit.
The rule as CMS states it
Medicare's claims processing manual, chapter 5, sets it out: for timed codes measured in 15-minute units, the total timed minutes in the visit decide the units. One unit is billed for 8 to 22 minutes, two for 23 to 37, three for 38 to 52, four for 53 to 67, and each further 15 minutes adds one. The minutes are totalled across the timed codes first, then the units are assigned to the codes by the minutes spent on each, with the code that had the most minutes taking any unit the remainder earns.
Three visits worked through
A visit with 40 timed minutes: 40 falls in the 38 to 52 band, three units. Split 25 minutes of therapeutic exercise and 15 of manual therapy, the exercise takes two units and the manual therapy one. A visit with 20 timed minutes: one unit, however the minutes were split, and the second code is not billed as a unit of its own. A visit with 53 timed minutes: four units, and a visit with 52 is three; the one minute is the difference the note has to document. The worksheet on this site returns the units for any total.
The untimed codes, counted separately
An evaluation, a re-evaluation, a hot or cold pack and the other service-based codes are billed as one unit each regardless of the minutes spent, and their minutes do not join the timed total. The visit's units are the timed units plus the untimed codes, which is the second figure the worksheet returns. Adding an untimed code's minutes to the timed total is the commonest way a clinic bills a unit it did not earn.
The counting mistakes that cost a unit or invite an audit
Counting units per code instead of on the total, which either over-bills or under-bills the split visits. Adding untimed minutes to the timed total. Billing a unit for a timed code with fewer than 8 minutes on its own when the total did not earn the extra unit. And documenting the total but not the minutes per code, which is what an auditor asks for. The plan of care and the documentation Medicare's benefit policy manual describes are what the count rests on; the register keeps the units per claim so a payer's question a year later is answered from the record.
The unit table, in full
One unit for 8 to 22 minutes. Two for 23 to 37. Three for 38 to 52. Four for 53 to 67. Five for 68 to 82. Six for 83 to 97. Seven for 98 to 112. Eight for 113 to 127. The pattern is fifteen minutes a unit with the first unit earned at eight, and the band edges are where the arithmetic is won or lost: a visit documented at 22 timed minutes is one unit, at 23 it is two, and the note's minutes per code are what the auditor reads against the units billed. The worksheet on this site returns the unit for any total and shows the band it fell in, which is the figure to check against the claim before it goes.
Assigning the units to the codes when the minutes are split
Total the timed minutes, read the units from the table, then give each code the units its own minutes earn and the remainder to the code with the most leftover minutes. A visit of 33 minutes of therapeutic exercise and 7 of manual therapy is 40 timed minutes, three units: two to the exercise for its first 30 minutes, and the third to the exercise again, because its 3 leftover minutes are fewer than manual therapy's 7 only if the manual therapy could earn a unit at all, and at 7 minutes on its own it cannot; the remainder unit goes to the code with the larger remaining minutes, which here is the manual therapy at 7 against the exercise's 3. Written out like that it is obvious why a clinic loses a unit on split visits and why the worksheet asks for the minutes per code rather than the total alone.
What the note has to show for the units to stand
The total timed minutes for the visit, the minutes per timed code, the untimed codes performed, and the total treatment time, each in the note for that date of service. Medicare's benefit policy manual expects the documentation to support the codes and units billed; an auditor who finds forty minutes documented as one line and three codes billed asks how the minutes were split, and a note that cannot answer loses the units. The register keeps the units as billed per claim beside the minutes as documented, so a question a year later is answered from the record rather than from the therapist's memory of a Tuesday.
Two clinics, one visit, two counts
The same 40-minute visit, 25 minutes of therapeutic exercise and 15 of manual therapy, billed by a clinic that counts on the total and by one that counts per code. On the total: 40 minutes, three units, two to the exercise and one to the manual therapy. Per code with a midpoint convention: exercise at 25 minutes earns two units (past the midpoint of the second), manual therapy at 15 earns one, three units again, and the clinics agree. Change the visit to 20 and 20: on the total, 40 minutes is still three units; per code, each 20-minute code earns one unit past its first midpoint and a second only past 22 or 23, so two units. Same visit, one unit apart, and the difference is the payer's method, not the therapist's work. The register keeps the method the claim was counted under against the payer, so the count is defensible to the payer that will read it.
Questions people ask about physical therapy billing units
How many billing units is a 45-minute physical therapy visit?
If all 45 minutes are timed codes, three units, because 45 falls in the 38 to 52 band. If 15 of those minutes were an untimed evaluation, the timed total is 30, two units, plus the evaluation as one unit.
Do commercial payers use the 8-minute rule?
Some follow Medicare's total-time method and some count units per code with a midpoint rule. The contract or the payer's policy says which; the worksheet on this site states the method it uses so you can compare.
Can I bill two timed codes with 10 minutes each?
Under the 8-minute rule the total is 20 minutes, one unit, assigned to one of the codes. The second code is documented but does not earn a separate unit.
Where is the 8-minute rule published?
In the Medicare Claims Processing Manual, chapter 5, section 20.2, which this page cites. The benefit policy manual's chapter 15 covers the documentation and the plan of care behind the claim.
Is the 8-minute rule the same as the AMA midpoint rule?
No. Medicare's rule totals the timed minutes across the visit and reads units from one table. The AMA's per-code convention bills a unit for a code once its own minutes pass the midpoint of fifteen, per code, without totalling. Some commercial payers follow one and some the other; the contract says which, and a clinic billing both has to count both ways.
Do the units change for occupational therapy or speech?
The timed-code rule is the same for occupational therapy under the GO modifier. Speech-language pathology codes are mostly untimed, one unit per session, so the table rarely applies. The worksheet counts whatever timed codes are entered under the same rule.
Sources
- Medicare Claims Processing Manual, chapter 5, section 20.2: the 8-minute rule and the unit table for timed therapy codes
- Medicare Benefit Policy Manual, chapter 15, section 220: covered outpatient rehabilitation therapy services and their documentation
- 42 CFR 410.60, Outpatient physical therapy services: conditions for coverage, including the plan of care