Coding and modifiers

How do you bill physical therapy services? A Medicare claim, line by line

Bill a Medicare physical therapy visit on a CMS-1500 or the 837P with one line per CPT code, the GP modifier on every line, units counted from total timed code minutes, and the certifying physician's NPI in item 17b. Each of these has a fixed place on the form, and CMS tells its contractors to return therapy claims that leave the therapy modifier off.

Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · Published October 26, 2026

Billing specialist checking a physical therapy claim against a treatment note and plan of care — Every field on a therapy claim traces back to the plan of care and the treatment note.

In short: a therapy claim is built from the plan of care. The certifying NPI, the GP modifier, the unit count and KX once the 2026 threshold is passed each have a field where they belong, and a missing one sends the claim back or lowers payment.

Which fields on the CMS-1500 matter for a therapy claim?

Seven places on the form carry the therapy-specific data. The table follows the Medicare Claims Processing Manual, chapter 26, for the paper form, and the electronic 837P carries the same data in its own segments.

Source: Medicare Claims Processing Manual, chapter 26, items 17, 21, 24A to 24J
Field	What goes in	Therapy point
Item 17 and 17b	Name of the certifying physician or nonphysician practitioner, qualifier DN, and the NPI in 17b	Chapter 5, section 10.3.5, says the certifying NPI must be on the therapy claim and is treated as a referring provider
Item 21	ICD-10-CM diagnoses in priority order, to the highest specificity for the date of service	The plan of care and the note have to support each one
Item 24A	Date of the service	The record needs a treatment note for each treatment day (Benefit Policy Manual, chapter 15, section 220)
Item 24B	Place of service code	POS 11 is the office; see the place of service rule
Item 24D	CPT code, then modifiers	The form holds up to four modifiers per line; GP belongs here
Item 24E	One diagnosis letter from item 21	The manual says one reference letter per line, the primary diagnosis for that service
Item 24G	Units	If only one service is performed, the numeral 1 must be entered
Item 24J	NPI of the rendering provider	The therapist who treated, not the group

Check the payer's own guide before you assume the same rules for a commercial plan. Some commercial payers read the diagnosis pointer field differently, and the unit logic can differ too.

Which modifiers go on each physical therapy line?

Every Medicare therapy line needs GP, because GP marks services delivered under an outpatient physical therapy plan of care. Chapter 5, section 10.4, tells contractors to return claims for the always-therapy codes when the therapy modifier is missing.

Sources: Claims Processing Manual, chapter 5, sections 10.3.3, 10.4 and 20; CR 13437; NCCI Policy Manual, chapter XI, section P
Modifier	When it goes on the line	What happens without it
GP	Every service under the physical therapy plan of care	The claim is returned
CQ	The service was furnished in whole or in part by a physical therapist assistant; always paired with GP	A CQ line without GP is rejected as unprocessable. With CQ, the line pays at 85 percent of the otherwise applicable Part B amount
KX	The patient's year-to-date allowed amount has passed the 2026 threshold of $2,480 for PT and SLP combined	Lines over the threshold without KX are denied
59 or XU	Two timed services done in separate, non-mingled time blocks where an NCCI edit applies	The second code is denied as bundled

CMS says providers may report the modifiers on a line in any order, so GP does not have to come first. If a line needs more than four, chapter 5 says to put 99 in item 24D and list the extra modifiers in item 19.

KX is an attestation, not a courtesy. By adding it you state that the services are reasonable and necessary, justified by the record, and eligible for the exception. Chapter 5 calls KX on low-cost services early in an episode, with no sign the threshold will be crossed, abusive. See the KX modifier page for the full rule.

Modifier 59 or XU is a last step, not a habit. The NCCI manual allows it only when the two procedures of an edit pair happened in different timed intervals, even if they ran back to back. The 59 versus XE, XS, XP and XU post shows how to choose, and the NCCI edits rule covers the edit itself.

How do you turn treatment minutes into the units in item 24G?

Add the minutes of the timed codes for the day, find the unit band for that total, and assign the units to the services in order of time spent. Untimed codes, such as an evaluation, take one unit however long they ran.

Only treatment time counts. Chapter 5, section 20.3, says the clock starts when the therapist or assistant is directly working with the patient, who is already in the treatment area and ready to begin. Rest breaks, toileting and waiting for equipment are not billed. When a stroke patient needs two staff in the parallel bars, each 15 minutes of treatment still counts as one unit, not two.

Section 20.2 sets the bands. One unit is 8 through 22 minutes, two units 23 through 37, three units 38 through 52, and four units 53 through 67. The total for the day caps the units, even when several services ran. The physical therapy billing page explains the 8-minute rule in full.

Example (illustrative, made-up minutes)

A visit has 28 minutes of therapeutic exercise (97110), 12 minutes of therapeutic activities (97530) and 5 minutes of manual therapy (97140). The timed total is 45 minutes, so the day supports 3 units.

97110, GP2 units: the first 15 minutes is one unit, and the 13 minutes left over is the largest remainder

97530, GP1 unit: its 12 minutes is the next largest remainder

97140Not billed: the 5 minutes sit outside the 3-unit cap, and the note still records them

The code pages for 97110 and the other therapy codes hold the descriptors in plain words. CPT descriptors are AMA copyright, so use your own licensed code book for the exact text.

What should you check before a therapy claim leaves?

Confirm the plan of care is certified. The Medicare Benefit Policy Manual, chapter 15, section 220.1.3, calls certification timely when it is signed or given as a verbal order and dated within 30 days after the first day of treatment, including the evaluation. A verbal order needs a signature within 14 days.
Put the certifying provider's NPI in item 17b, with qualifier DN in item 17.
Look at every line for GP, and for CQ only where an assistant did part of the work.
Match units to the minute bands. If the total timed minutes are 45, three units is the ceiling.
Check the year-to-date allowed amount against $2,480 and add KX on the lines that cross it.
Look for a second evaluation. The NCCI manual allows a physical therapist one evaluation or re-evaluation (97161 to 97164) on a single date of service.

What do the common therapy denials mean on the remittance?

Read the CARC and RARC on the 835 first, then fix the field that caused it. X12 defines the codes below.

CARC wording: X12 claim adjustment reason codes
What you see	What it means	Fix
Claim returned or rejected	Therapy modifier missing, or CQ sent without GP	Add GP, or pair CQ with GP, and resubmit
CARC 4	The procedure code is inconsistent with the modifier used	Check that the code is a therapy code and the modifier matches the discipline
CARC 97	The benefit is included in the payment for another service already adjudicated	Check whether the two services ran in separate timed blocks; if the note supports it, add 59 or XU
Denied above the threshold	KX missing on a line past $2,480	Correct the claim with KX only if the record supports the attestation
CARC 50	Payer does not deem the service medically necessary	Send the evaluation, plan of care and progress notes that show skilled need
CARC 151	Information does not support this many or this frequency of services	Send the notes and the plan of care frequency

CMS does not name the CARC that goes with a therapy line denied for a missing KX, so read the remit for the actual code. Our denial management service works each one against the note, not just the code.

How Nucleus Align handles it

We check therapy claims against these fields before they leave: modifiers, unit bands, certification dates and the KX amount. Claims go out within 24 hours of charge entry and denials are worked within 48 hours. More claim walkthroughs are on the blog. To see how your therapy claims line up, book a call.

Sources

We check every rule, code and deadline against the official source. See our editorial policy.

Written by Salman Saeed, CEO and Co-Founder

Reviewed by a Certified Medical Coder. Our editorial policy explains how every article is checked.

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01How do you bill physical therapy services to Medicare?

Send one claim line per CPT code on a CMS-1500 or 837P, with GP on every line, units counted from total timed minutes, and the certifying physician's NPI in item 17b. Add CQ when a physical therapist assistant did part of the work, and KX once the year's allowed amount passes the threshold.

02Which modifier goes on every Medicare physical therapy line?

GP, which marks services delivered under an outpatient physical therapy plan of care. Claims Processing Manual chapter 5 tells contractors to return always-therapy codes that arrive without a therapy modifier. GO is the occupational therapy modifier and GN is the speech-language pathology modifier.

03Where does the certifying physician's NPI go on a therapy claim?

In item 17b of the CMS-1500, with the physician's name in item 17 and qualifier DN. Chapter 5, section 10.3.5, says the NPI of the certifying physician or nonphysician practitioner must be on the therapy claim and is treated as a referring provider.

04How many modifiers fit on one CMS-1500 line?

Four. Chapter 26 says the form can capture up to four modifiers in item 24D. For a therapy line with more, chapter 5 says to enter 99 in item 24D and list the additional modifiers in item 19. CMS also says therapy modifiers may be reported in any order.

05What is the KX threshold for physical therapy in 2026?

$2,480 for physical therapy and speech-language pathology combined, according to CMS Change Request 13437. Claims for therapy above that amount without the KX modifier are denied. Adding KX is an attestation that the services are reasonable, necessary and supported by the record.

Specialty

Physical therapy billing