5 Physical Therapy Billing Mistakes That Cost Clinics Thousands: 97110 Units, KX and GP

The five physical therapy billing mistakes that cost clinics the most are miscounted 8 minute rule units on codes like 97110 and 97140, a missing or misused KX modifier at the therapy threshold, an uncertified plan of care, a missing GP modifier, and treatment notes that do not record total timed minutes.

Each one produces a predictable payer response: a unit reduction, a line denial, a medical review request, or a recoupment months later. Below is what goes wrong in each case, what the payer does, and the fix as steps your front desk, therapists and billers can follow. For a deeper look at unit math alone, see our guide to the physical therapy 8 minute rule.

Mistake 1: Counting 8 Minute Rule Units Code by Code

CMS bills timed codes such as 97110, 97112, 97140 and 97530 in 15 minute units. The Medicare Claims Processing Manual, Chapter 5, Section 20.2, sets the scale: one unit for 8 through 22 minutes, two units for 23 through 37 minutes, three units for 38 through 52 minutes, and so on. The error most clinics make is applying that scale to each code separately. When more than one timed code is performed in a day, CMS says the total number of timed minutes determines the total number of units billed.

CMS gives its own example: 33 minutes of 97110 and 7 minutes of 97140 is 40 timed minutes, which supports three units, billed as two units of 97110 and one unit of 97140. A clinic counting code by code drops the 97140 unit because 7 minutes alone is under 8. The reverse error is just as common. In another CMS example, four timed services totaling 49 minutes support only three units, so the fourth service is documented but not billed. Code by code counting bills four, and Medicare cuts the extra unit. CMS also says a provider who consistently bills less than 15 minutes for a unit should be highlighted for review.

The fix:

1. Add up all timed minutes for the date of service first.
2. Convert the total to units using the Section 20.2 table.
3. Assign units to codes starting with the code that has the most minutes.
4. When two codes each run 7 minutes or less but total 8 or more, bill one unit for the code with more minutes.
5. Apply the same total time logic to commercial plans that state they follow CMS, and check each contract for plans that do not.

Mistake 2: Missing the KX Modifier at the Therapy Threshold

The Bipartisan Budget Act of 2018 repealed the hard therapy cap but kept the old cap amount as a threshold. Once a beneficiary’s incurred physical therapy and speech language pathology expenses pass that amount in a calendar year, every claim line must carry the KX modifier to attest that the services are medically necessary and documented. CMS set the threshold for calendar year 2026 at $2,480 for physical therapy and speech language pathology combined, according to MLN Matters MM14315. The amount changes every January, so confirm the current figure each year.

Chapter 5 is blunt: if a claim is submitted without KX modifiers and the threshold is exceeded, those services will be denied. The opposite error also hurts. Chapter 5 warns that applying KX to all services on claims below the threshold, or to every beneficiary a clinic treats, may invite contractor scrutiny. A separate targeted medical review threshold of $3,000 still applies, and Noridian notes it will be updated by the Medicare Economic Index starting in calendar year 2028.

The fix:

1. Track each Medicare patient’s year to date therapy spend at intake, including care from other clinics, using the eligibility response.
2. Flag the chart before the patient crosses the threshold.
3. Have the treating therapist document why continued skilled care is needed before KX goes on the claim.
4. Never add KX by default to claims under the threshold.
5. Expect records requests once a patient passes $3,000 and keep progress reports ready.

Mistake 3: An Uncertified or Expired Plan of Care

Medicare pays outpatient therapy only under a plan of care certified by a physician or nonphysician practitioner. The Medicare Benefit Policy Manual, Chapter 15, Section 220.1.3, says initial certification is timely when it is signed and dated within 30 days of the first treatment, including the evaluation. A verbal order must be followed by a signature within 14 days. Recertification is due at least every 90 days, or sooner when the plan changes significantly.

Since January 1, 2025, CMS allows an exception to the signature requirement for initial certification. Under MLN Matters MM13887, the exception applies when a written order or referral from the patient’s physician or practitioner is on file and the therapist has documented evidence of sending the plan of care to that practitioner within 30 days of the initial evaluation. The American Physical Therapy Association describes this as allowing “a signed and dated order or referral to meet the certification requirements.” The exception covers initial certification only. Recertification at 90 days still needs a signature.

When certification is missing, payment may be denied for every visit in the uncovered interval, and those denials often surface during a postpayment review long after the patient has been discharged.

The fix:

1. Confirm a signed order or referral is in the chart before the evaluation.
2. Send the plan of care the day it is written and save the fax or portal confirmation.
3. Calendar the 90 day recertification date in the scheduling system, not in a therapist’s memory.
4. Hold claims for visits past the certified end date until a signed recertification arrives.
5. If certification is late, obtain a delayed certification with the reason for the delay, as Section 220.1.3 permits.

Mistake 4: Leaving Off the GP Modifier

The Medicare Claims Processing Manual, Chapter 5, Section 20.1, requires one of three discipline modifiers on every code on the therapy code list: GP for services under a physical therapy plan of care, GO for occupational therapy and GN for speech language pathology. The rule applies to claims from physicians, nonphysician practitioners, private practice therapists and facilities. Medicare uses these modifiers to track the KX threshold, so a missing GP sends the line back as unprocessable.

Wellpoint’s Massachusetts commercial policy C07002 says “always therapy” services must be reported with GN, GO or GP. UnitedHealthcare’s commercial policy uses those same modifiers to separate disciplines inside a multispecialty group, which matters for the unit limit covered below.

The fix:

1. Map GP to every therapy code in the charge master for physical therapists and assistants.
2. Report only one discipline modifier per line.
3. When a physician practice bills therapy under a physical therapy plan of care, apply GP there as well.
4. Under Medicare, add CQ for services furnished in whole or in part by a physical therapist assistant; Chapter 5 requires CQ to be paired with GP.

Mistake 5: Notes That Do Not Record Total Timed Minutes

Unit counts are only as defensible as the note behind them. Chapter 15, Section 220.3, requires each treatment note to include the date, each intervention billed in language that can be matched to the claim, the total timed code treatment minutes and the total treatment time in minutes. CMS states that the billing and the total timed code treatment minutes must be consistent. Rest periods and other nonbillable time do not count.

When an auditor finds four units billed against a note showing 45 timed minutes, the fourth unit is recouped, and the same error repeated across a year of visits becomes an extrapolated overpayment demand.

The fix:

1. Build required fields for total timed minutes and total treatment time into the note template.
2. Record every timed service performed, even ones not billed, since CMS says unbilled timed services can affect billing.
3. Compare billed units to documented minutes before each claim goes out.
4. Make sure the treating clinician signs with credentials, and note supervision when an assistant provides care.

Which Payers Are Strictest?

Medicare sets the baseline with the KX threshold, the $3,000 targeted review threshold and the certification clock. UnitedHealthcare commercial and Individual Exchange plans add a limit of their own. Policy 2026R0101A pays up to four timed codes, equal to one hour of therapy, per date of service by the same specialty provider. Units beyond four that are correctly billed are considered only on a reconsideration request.

UnitedHealthcare does allow four timed codes for each specialty type within a multispecialty group under one tax ID, which is one more reason a correct GP or GO modifier protects revenue. Wellpoint’s Massachusetts commercial plan follows the CMS unit table and documentation rules closely, so a Medicare compliant claim usually passes there too.

The WeBill Health Take

WeBill Health keeps internal payer rule libraries organized by specialty and by carrier, so a physical therapy claim to UnitedHealthcare is checked against its four unit limit while the same visit for a Medicare patient is checked against the KX threshold and the certification dates. A coder reviews every claim before submission, comparing billed units to the documented minutes and confirming the GP modifier and plan of care dates. That human pre submission review is how we hold a 98% clean claim rate for the clinics we support on our physical therapy billing services page, and you can read about the denial patterns we see most in physical therapy billing denials.

Frequently Asked Questions

Does the 8 minute rule apply to commercial insurance?

Many commercial plans adopt it. UnitedHealthcare’s commercial policy states it aligns with CMS on the 8 minute minimum, and Wellpoint’s Massachusetts commercial policy reproduces the CMS unit table. Check each contract, since some plans count units per code.

What is the KX modifier threshold for physical therapy?

For calendar year 2026, CMS set it at $2,480 for physical therapy and speech language pathology combined. CMS updates the amount each year, and a separate $3,000 targeted medical review threshold also applies.

Does a physician still need to sign a Medicare plan of care?

For initial certification, not always. Since 2025, a signed order or referral on file plus proof the plan was sent within 30 days of the evaluation meets the requirement. Recertification still needs a signature.

What should I look for in a physical therapy billing company?

Look for a physical therapy billing company that keeps carrier specific rules for unit limits, KX thresholds and certification dates, reviews units against documented minutes before submission, and can report denials by payer and by reason. Ask how it tracks recertification dates for each patient.

Want to know which of these five mistakes is costing your clinic? Request a Revenue Defense Audit.

Sources

• CMS, Medicare Claims Processing Manual, Chapter 5, Part B Outpatient Rehabilitation and CORF/OPT Services
• CMS, Medicare Benefit Policy Manual, Chapter 15, Covered Medical and Other Health Services
• CMS, MLN Matters MM14315, Medicare Physician Fee Schedule Final Rule Summary CY 2026
• CMS, MLN Matters MM13887, Medicare Physician Fee Schedule Final Rule Summary CY 2025
• Noridian Medicare, Per Beneficiary KX Modifier Thresholds
• UnitedHealthcare, Physical Medicine and Rehabilitation Maximum Combined Frequency per Day Policy, 2026R0101A
• Wellpoint Massachusetts, Guidelines for Reporting Timed Units for Physical Medicine and Rehabilitation Services, C07002
• American Physical Therapy Association, Medicare’s New Exception to the Plan of Care Certification Requirement