KX is an attestation, not an override. Appending it does not unlock a benefit, extend a limit or tell the payer to pay. It is a statement that you hold documentation proving the service is medically necessary and meets the payer’s coverage criteria — and that you will produce that documentation if asked.
That distinction is the whole page. Billers treat KX as the character you add to make a denial go away. It is closer to a signature: nothing about the claim changes except that you have made a statement the payer can later ask you to stand behind.
Medicare tracks each beneficiary’s therapy charges across the calendar year, across every provider who treats them. Once the year-to-date total passes the annual threshold, further claims submitted without KX are denied. With KX, they continue to process.
The grouping catches people out more often than the amount does. Physical therapy and speech-language pathology share one threshold. Occupational therapy has its own. A patient receiving PT and SLP is burning a single allowance twice as fast as the biller watching two separate service lines expects.
The 2025 threshold amount was 2,410 US dollars. CMS indexes it annually and publishes the figure with the Physician Fee Schedule, so confirm the current value with your MAC rather than carrying last year’s number forward. To see where a specific patient stands, put their year-to-date charges into the therapy threshold calculator.
| Threshold | What happens when you cross it |
|---|---|
| KX threshold (indexed annually) | Claims are denied unless KX is appended. Append it and billing continues. |
| Targeted medical review threshold (3,000 US dollars) | Nothing is denied. The claim becomes eligible for selection for medical review — selection is not automatic. |
Crossing the review threshold is routinely misread as a second cap. It is not. Care does not stop and payment does not stop. What changes is your exposure: documentation that was adequate when nobody looked at it becomes the only thing standing between you and a recoupment if someone does.
On durable medical equipment claims, KX carries the same meaning against a different rulebook: the coverage criteria in the applicable local coverage determination have been met and the supporting documentation is on file. Suppliers use it constantly, and the therapy-only explanations found in most billing guides leave them without an answer.
The logic transfers cleanly. Whatever the setting, KX says I have checked the criteria and I have the paperwork. What differs is which criteria and whose paperwork.
The failure mode is blanket application: once a patient crosses the threshold, KX goes on every subsequent line automatically, because otherwise the claims deny. It works, which is exactly the problem.
Each appended KX is a fresh attestation about that specific service on that specific date. Adding it reflexively means attesting to something nobody verified, on every line, repeatedly — and doing so in a category of claim already flagged for targeted review. That is how a billing shortcut turns into False Claims Act exposure, and it is a well-travelled route.
The defensible workflow is unglamorous: check that the plan of care is current, that progress notes actually show progress toward stated goals, and that continued skilled therapy is justified on its own terms. Then append the modifier.
Therapy threshold calculator — where a patient sits against the KX and review thresholds. 8 minute rule calculator — converting treatment minutes into billable units before any of this applies. The 8-minute rule for PT billing and physical therapy billing.
Threshold tracking, KX attestation and the documentation behind it are part of full revenue cycle management — and the first week is free.
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