PT billing units

Physical therapy billing units, PT billing units

Physical therapy billing units are important for any physical therapist practicing outside of a cash-based practice. PT billing units are an essential part of receiving payment from contracted insurance providers for your services. Depending on the intervention you provide your patient and the patient’s insurance plan, the rules for PT billing units will vary. Let’s take a deeper look into PT billing units to help you feel confident you are getting the most out of each session.

Click here to enroll in our free on-demand Insurance Billing for Therapists video course [Enroll Now]

What are PT billing units and why are they important?

Let’s face it, most therapists would prefer to focus on patient care and not on the financial aspect of the business. Many clinics are feeling the squeeze of reduced reimbursement rates for physical therapy services from big insurance companies, however. While patient care takes precedence, optimal PT billing unit practices are a close second.  When it comes to billing, a unit of service will be attached to either a timed or untimed CPT Code. CPT codes are current procedural terminology codes. CPT codes are utilized to describe the physical therapy services rendered when submitting a claim to a third party payer. A therapist will select a CPT code based on the type of interventions they used. Common CPT codes include 97110 (therex), 97140 (manual therapy) and 97161 (low complexity evaluation). 

Most PT billing unit codes are described in terms of 15-minute units of service. The payor source determines how many minutes of service are required to be delivered before a therapist can bill for a single unit of care and also how many PT billing units of service can be billed within a treatment session of a given length. In addition to timed codes, there are also many untimed codes. In this case only one unit of service will be billed no matter how long the intervention lasts. One of the most important things to know is whether the insurance plan follows Medicare’s 8-minute rule

Medicare 8-minute rule

Medicare insurance created the “8-minute rule” to delineate exactly how providers like physical therapists can bill for their services. It is important to note that while this rule was created by Medicare, many other payer sources like Medicaid, some federal and even commercial plans also follow this rule. The 8-minute rule stipulates that at least 8 minutes of a single intervention must be administered in order to bill for one CPT unit. While one might think that one can then bill for two units after 16 minutes of treatment have been completed, that would be too simple. 

The Medicare 8-minute rule stipulates that 23 minutes of service have to be provided in order to bill for two units of service and 38 minutes for 3 units of service. See the chart below to learn how many units can be billed based on the length of the treatment session. 



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 minutes

6 units

Example 1

24 minutes of 97112 neuromuscular re-education

(qualifies as 2 units)

15 minutes of 97110 (therex)  

(qualifies as 1 unit)

18 minutes of 97116 gait training

(qualifies as 1 unit)

Total minutes= 57  

(able to bill for all 4 units)

Example 2

12 minutes of 97140 manual therapy

(qualifies as 1 unit)

23 minutes of 97110 therex

(qualifies as 2 units)

17 minutes of 97112 neuromuscular re-education

(qualifies as 1 unit)

Total minutes = 52

(able to bill for only 3 units)

Example 3

35 minutes of 97110 therex

(qualifies as 2 units)

10 minutes of 97035 ultrasound (timed)

(qualifies as 1 unit)

30 min of 97014 electrical stimulation unattended (untimed)

(qualifies as 1 unit)

12 min of 97112 neuromuscular re-education

(qualifies as 1 unit)

Total minutes = 87 minutes

(qualifies as 5 units)

According to the chart above, this can qualify as 6 PT billing units of treatment based on a total treatment time of 87 minutes HOWEVER, only the timed codes count toward the total treatment time which totals 57 minutes which qualifies for only 4 units PLUS the 1 untimed unit available for a supervised modality like unattended electrical stim. 

When it comes to supervised and constant attendance modalities, the Centers for Medicare and Medicaid Services stipulates under what conditions more than one unit can be billed within a 15 minute time period. 

Start 30-day Free Trial and explore TheraPlatform. HIPAA Compliant Video and Practice Management Software for Therapists.

Mixed remainders and the Medicare 8-minute rule

Now that you understand the 8-minute rule, we are going to complicate it slightly by discussing the rule of Mixed Remainders. Medicare considers one PT billing unit of service to be 15 min. They allow for the possibility of gaining an extra unit of billing in a case where the number of minutes of 2 or more interventions is beyond 15 minutes, 30 minutes, 45 minutes, etc. but less than the number of minutes that would qualify for an extra unit (e.g., 23 minutes, 38 minutes, etc.)

If the total remaining minutes is 8 minutes or greater, Medicare will allow you to bill one extra unit of the CPT code that has the most remaining minutes.

Let’s have a look:
  • Therapeutic Exercise 97110: 18 minutes  1 unit + 3 additional minutes remaining

  • Neuro Re-ed 97112: 20 minutes  1 unit + 5 additional minutes remaining

Total treatment time equals 38 minutes which qualifies for 3 units BUT you only provided 1 unit worth of therapeutic exercise and 1 unit worth of neuromuscular re-education which equals 2 units. The rule of mixed remainders, however, states that the 3 remaining minutes of therex and the 5 remaining minutes of neuro re-ed equal at least 8 minutes which allows for an additional unit of neuro re-ed to be billed which totals 3 units. 

Start Your Free Trial Now

Non-Medicare insurance

While it may seem safest to just use the 8-minute rule all the time, if an insurance plan does not follow the 8-minute rule, you may be missing out on the opportunity to bill for additional PT billing units. Some commercial plans follow the Substantial Portion Methodology (SPM) which states that you can bill for any unit of service that is provided for a “substantial portion” of a 15-minute time period (ie. at least 8 minutes). Under SPM, if you perform 9 minutes of manual therapy and 10 minutes of therapeutic exercises (19 minutes total) you can bill for one unit of each. The only way to know if a specific payer follows the 8-minute rule or SPM is to ask.


While this may seem like a lot to consider, Theraplatform, a fully integrated EHR, practice management and teletherapy tool has you covered. Theraplatform is designed to make PT billing units and reconciliation simple so you can focus on the patient care that matters most. They also offer a 30-day trial for free. No credit card required and cancel anytime.

More resources
Free video classes

Practice Management, EHR/EMR and Teletherapy Platform

Exclusive therapy apps and games

Start 30 Day FREE TRIAL
8 minute rule; eight minute rule; time based codes; timed CPT codes
The 8-minute rule for therapy billing

The 8-minute rule allows therapists to bill for a specific timed service. Learn when it starts, how it works, and time-based vs. service-based codes.

modifier59, modifier59 for physical therapy,
Modifier 59

While billing and claim submission are not fun, learning about effective billing practices including how to use Modifier 59, can keep your practice profitable.

Subscribe to our newsletter