Physical Therapy Billing Services

The 8-Minute Rule, Recalculated

A PT clinic's timed-code unit engine, with KX at the threshold and CQ on assistant minutes, so the units on the claim and the modifiers on the line finally tell the same story.

The short answer: billable units come from your total timed minutes, not from rounding each code on its own. Add them up, read the unit off the 8-minute table, then hand the leftover minutes to the code with the largest remainder. Only after the units are right do you tag KX at the therapy threshold and CQ where a PTA did the work.

Rule of eights: 8 min = 1 unit Untimed codes: 1 unit, no clock KX at the CY2026 threshold CQ over the 10% de minimis

Try it on a real visit

Total minutes in. Units, KX and CQ out.

Enter the timed minutes per code and the assistant minutes inside each one. The panel sums the total, reads the unit off the CMS table, allocates the remainder, and flags where KX and CQ belong. Nothing leaves your browser.

Timed CPT codes

15-minute codes. "PTA min" is the portion furnished by a physical therapist assistant.

CodeTotal minPTA min

97110Therapeutic exercise

97140Manual therapy

97112Neuromuscular re-education

97530Therapeutic activities

UNTIMED / SERVICE-BASED (1 unit each, minutes ignored)

97010 hot/cold packs 97012 traction 97014 unattended e-stim

Patient therapy $ used YTD

KX threshold (PT + SLP)

2 billable
units total timed
28 min

The table everyone half-remembers

One table, read from total minutes

CMS counts every timed minute in the visit, then converts the sum. A leftover of 8 or more minutes buys the next unit. Fewer than 8, it stays behind. This is total minutes, not per-code.

8 – 22 min1

23 – 37 min2

38 – 52 min3

53 – 67 min4

68 – 82 min5

83 – 97 min6

The trap that costs money: two timed codes at 8 minutes each is 16 total minutes, which is one unit, not two. Bill both and you have an overpayment. The calculator above catches exactly this. Source: CMS Medicare Claims Processing Manual, Pub. 100-04, Chapter 5, Section 20.2.

The order of operations

Units first, modifiers second, always

The mistake is tagging KX and CQ onto lines whose units are already wrong. Do it in this order and the claim reconciles on the first pass.

Sum the timed minutes

Add every 15-minute code. Untimed codes like 97010 sit out. This total drives the unit count.

Read the total unit

Convert the sum on the 8-minute table. That number caps the units you can spread across all timed codes.

Allocate the remainder

Give each code its full 15-minute blocks, then the leftover unit goes to the largest remaining minutes.

Tag KX and CQ

Add KX once the patient crosses the threshold, and CQ on any code where the PTA did over 10%.

Two modifiers, two different questions

KX asks "how much." CQ asks "who."

They are not interchangeable and they are not optional once triggered. One tracks dollars against the annual threshold. The other tracks assistant time against the service.

The therapy threshold

KX certifies the services above the annual threshold are medically necessary and documented. It is not a cap you cannot exceed, it is the point where you attest.

PT and SLP share one combined threshold. OT has its own.
The dollar amount is updated every year in the Medicare Physician Fee Schedule. Confirm the CY2026 figure in the final rule before go-live.
A separate $3,000 targeted medical review threshold stays in place through CY2027 under the Bipartisan Budget Act of 2018. Crossing it can invite review, not denial.
Miss KX above the threshold and the line denies. Add it without support in the record and you carry audit risk.

CY2026 Medicare Physician Fee Schedule Final Rule; Social Security Act 1833(g)

The assistant modifier

CQ flags services furnished in whole or in part by a physical therapist assistant. Its sibling CO does the same for occupational therapy assistants.

The de minimis standard: CQ applies when the PTA furnishes more than 10% of a service's total time.
CQ lines are paid at 85% of the fee schedule, a 15% reduction, in effect since CY2022 under Section 1834(v) of the Social Security Act.
It is decided per code, not per visit. One line can carry CQ while another on the same claim does not.
Get the minute split wrong and you either underpay yourself or overbill Medicare. Both surface in audit.

CMS CQ/CO policy; Social Security Act 1834(v); effective CY2022

Where the units quietly go wrong

Three leaks the calculator plugs

Per-code rounding

Rounding each code alone

Eight minutes here and eight there billed as two units when the 16-minute total supports only one. Repeat it across a schedule and the takebacks add up.

Wrong remainder

Remainder on the wrong code

The leftover unit belongs to the code with the most unspent minutes. Put it on the lower-value code and you leave allowed dollars on the table.

Modifier drift

KX and CQ out of sync

Units say one thing, modifiers say another. A KX-less line above the threshold denies, and a missing CQ on assistant time is a compliance flag waiting to be found.

Guidelines cited on this page

CMS Medicare Claims Processing Manual, Pub. 100-04, Chapter 5, Section 20.2, counting minutes for timed codes (the 8-minute rule).
CY2026 Medicare Physician Fee Schedule Final Rule, annual KX modifier therapy threshold amounts for PT/SLP and OT.
Targeted medical review threshold of $3,000, extended through CY2027 by the Bipartisan Budget Act of 2018.
CQ and CO modifiers for services furnished by PTAs and OTAs, 10% de minimis standard and 15% payment reduction, Section 1834(v) of the Social Security Act, effective CY2022.
CPT timed codes 97110, 97112, 97116, 97140, 97530 versus service-based codes 97010, 97012, 97014.
American Physical Therapy Association (APTA) billing and coding guidance on the de minimis standard and unit counting.

Physical therapy billing services, done at the line level

Your minutes are correct. Are your units and modifiers?

ASP-RCM builds this logic into the claim before it goes out: total-minute unit math, remainder allocation, KX at the threshold, and CQ on every assistant line. Fewer denials, cleaner audits, and the dollars you already earned. Let us run a sample of your PT claims and show you the delta.

Book a PT claims review

ASP-RCM Solutions · Senior Partner · Frisco, TX

This tool and page are educational and reflect Medicare rules for timed therapy codes. Commercial and Medicaid payers vary. Confirm current-year threshold amounts in the CY2026 MPFS final rule and your payer policies before billing.