Skilled nursing facilities use CPT codes only for Part B therapy and outpatient services, not for Part A stays. Part A is paid a per-diem under PDPM using a HIPPS code derived from the MDS. Part B claims use CPT codes with therapy modifiers GP, GO, or GN on type of bill 22X or 23X.

The most common coding question in a skilled nursing business office rests on a false premise. People ask which CPT codes to use for a Part A resident, and the answer is none. Part A pays a daily rate built from an assessment, and no procedure code changes it.

Getting this distinction right prevents two expensive errors: attempting to bill Part B services for a resident in a covered Part A stay, and failing to bill Part B services for a resident who is not.

Key takeaways

• Part A SNF stays are paid per diem under PDPM. The claim carries a HIPPS code from the MDS, not CPT codes.
• Part B therapy for residents outside a covered Part A stay is billed with CPT codes on type of bill 22X.
• Every therapy CPT line needs a discipline modifier: GP for physical therapy, GO for occupational therapy, GN for speech-language pathology.
• Timed therapy codes are billed in 15-minute units under the 8-minute rule; untimed codes bill once per discipline per day.
• Consolidated billing determines who may bill during a Part A stay, and the facility is usually responsible.
• HCPCS Level II codes cover supplies, drugs, and equipment that CPT does not.

Part A: no CPT codes at all

During a covered Part A stay, the facility submits a 21X type of bill and receives a per-diem determined by PDPM classification. The payment-relevant code on the claim is the HIPPS code, a five-character string derived directly from the transmitted MDS.

Revenue codes appear on the claim to describe accommodation and ancillary categories, and diagnosis codes appear and matter enormously — the primary diagnosis at MDS item I0020B drives PT, OT, and SLP classification. But procedure codes do not set the rate. See the PDPM guide for how the per-diem is constructed.

The practical implication for staff: if the payment on a Part A claim is wrong, no coding change on the claim will fix it. The assessment is wrong.

Part B: where CPT codes apply

Residents who are not in a covered Part A stay — benefit days exhausted, no qualifying hospital stay, or long-term care residents — may still receive medically necessary therapy billable to Part B. This is where CPT coding lives.

Therapy discipline modifiers

Every therapy service line must carry one:

Omitting the discipline modifier is one of the most frequent and most easily avoided rejections in SNF Part B billing.

Commonly used therapy CPT codes

This is an orientation list, not an exhaustive one, and CPT is revised annually by the AMA. Verify against the current code set and your MAC's local coverage determinations.

The 8-minute rule

Timed codes bill in 15-minute units, and the number of units follows total timed minutes: 8 to 22 minutes is one unit, 23 to 37 is two, 38 to 52 is three, 53 to 67 is four, and so on in 15-minute increments. Untimed codes bill once per discipline per day regardless of duration.

Mixing timed and untimed services in a session and billing both by duration is a recurring error.

The KX modifier

Medicare applies an annual therapy threshold. Above it, the KX modifier attests that services remain medically necessary and that the record supports it. A second, higher threshold triggers targeted medical review.

KX is an attestation, not a formality. Appending it to a claim the documentation cannot support is exactly the pattern medical review is designed to find.

Consolidated billing: who is allowed to bill

During a covered Part A stay, most services furnished to the resident are bundled into the facility per-diem, and the facility — not the outside provider — is responsible for payment. An outside supplier who bills Medicare directly for a bundled service will be rejected, and will then bill you.

A limited set of high-cost services is statutorily excluded and separately billable by the outside provider, including certain physician professional services, specified chemotherapy and radioisotope services, and some high-cost surgical and diagnostic procedures. See the consolidated billing guide for the exclusion categories.

The operational control: verify Part A status before authorizing any outside service, and put consolidated billing language in outside provider agreements.

CPT versus HCPCS Level II versus revenue codes

Institutional claims pair procedure codes with revenue codes. Therapy lines commonly pair with revenue code 042X for physical therapy, 043X for occupational therapy, and 044X for speech-language pathology.

The coding errors that cost the most

1. Attempting CPT coding on a Part A claim. The stay is per-diem; the codes do nothing.
2. Missing GP, GO, or GN. Straight rejection.
3. Unit miscounts under the 8-minute rule. Especially where a session mixed timed and untimed services.
4. KX applied without supporting documentation. An attestation the record cannot defend.
5. Billing Part B during a covered Part A stay. The service was already bundled.
6. Missing Part B revenue entirely for long-term care residents receiving therapy. The mirror-image error, and quieter.
7. Revenue code and CPT mismatch.
8. Using a prior-year code set. CPT changes annually.

Where AI helps with SNF coding

Coding accuracy in skilled nursing is largely a documentation-comparison problem, which is work a HIPAA-compliant AI platform handles directly:

• Pre-bill review. Compare therapy documentation against billed CPT lines and units, and flag where minutes do not support the units claimed.
• Modifier audit. Identify therapy lines missing a discipline modifier before submission.
• Part A and Part B status check. Cross-reference service dates against covered Part A days to catch overlap in both directions.
• KX support review. Read the therapy record and assess whether documentation supports the medical necessity attestation.
• Consolidated billing triage. Read an outside provider invoice and determine whether the service was bundled.

Hathr.AI runs Anthropic Claude models inside AWS GovCloud under a FedRAMP High authorization boundary, signs a Business Associate Agreement within 24 hours on every plan, and reads scanned and handwritten therapy documentation that most tools reject outright.

The boundary: AI does not assign codes. It compares what was billed against what was documented and surfaces the mismatch for a certified coder to resolve.

Test it on one week of therapy claims

Upload a week of therapy documentation and the corresponding billed lines, and ask Hathr.AI where units and modifiers do not reconcile.

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Frequently asked questions

Do SNFs use CPT codes for Part A stays?
No. Part A skilled nursing stays are paid a per-diem under PDPM, and the claim carries a HIPPS code derived from the MDS rather than CPT procedure codes.

What CPT codes do SNFs use for therapy?
Part B therapy uses standard therapy CPT codes such as 97110 therapeutic exercise, 97116 gait training, 97530 therapeutic activities, and 92507 speech-language treatment, each with a discipline modifier.

What are the GP, GO, and GN modifiers?
They identify the therapy discipline: GP for physical therapy, GO for occupational therapy, and GN for speech-language pathology. Every therapy line requires one.

What is the 8-minute rule?
Timed therapy codes bill in 15-minute units based on total timed minutes. Eight to 22 minutes is one unit, 23 to 37 is two units, and so on.

What bill type does a SNF use for Part B services?
Type of bill 22X for Part B services to residents not in a covered Part A stay, and 23X for outpatient services.

What is the KX modifier?
An attestation that therapy above the annual threshold remains medically necessary and that the medical record supports it.

Part of the HIPAA-Compliant AI for Skilled Nursing Facilities hub. Related: SNF Billing Guide · Appealing a Medicare Denial

Code references are for orientation only and reflect the code set as of August 2026. CPT is maintained and revised annually by the American Medical Association. Verify all codes, modifiers, and thresholds against the current code set and your MAC guidance before billing.