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N639 Remark Code: Inpatient Rehab Facility Pricing

N639 means the payer priced the stay under its inpatient rehabilitation facility (IRF) fee schedule. It is a payment-method note rather than a denial, and the amount above the allowed rate is typically a contractual adjustment.

Quick facts

Code
N639 (RARC N639)
Status
Active In use since July 15, 2013.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The gap between the facility's charges and the IRF schedule amount is the facility's write-off under its contract or the governing program.
  • PR (Patient Responsibility): Patient cost-sharing, where the plan applies it to the rehab stay, is reported under PR.
Official description
Reimbursement has been made according to the inpatient rehabilitation facilities fee schedule.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N639 means

Inpatient rehabilitation facilities, whether freestanding hospitals or distinct rehab units inside acute hospitals, are often paid on their own methodology. Medicare, for example, pays IRFs under a prospective payment system built on patient case-mix groups rather than itemized charges, and many Medicaid and commercial payers have their own IRF rates.

N639 is the payer’s way of saying that methodology was the basis for this claim. It is generally paired with CARC 45, which reports the reduction amount, while the remark explains the pricing source.

Who sees it

Almost always the facility, on an institutional claim for an inpatient rehab stay. If a remittance for an acute inpatient stay, a skilled nursing stay, or an outpatient service carries N639, that is a signal the claim may have been classified in the wrong setting.

Checking the payment

Rehab payments depend on more than a single fee. Before accepting or disputing the amount, confirm:

  • The admission and discharge dates and the number of days the payer recognized.
  • The patient classification the payer used, where the methodology relies on one, and whether it matches the assessment your facility submitted.
  • The rate year applied, which should match the discharge or service dates under the payer’s rules.
  • Any transfer or short-stay adjustments listed alongside the payment.

What to do

  1. If everything matches, post the reduction as a contractual adjustment and bill the patient only for amounts marked PR.
  2. If the classification or dates are wrong, correct the source data and submit a replacement claim under the payer’s institutional rules.
  3. If the rate is wrong, contact the payer with your contract or the published rate and ask for reprocessing, or file a reconsideration within its deadline.
  4. If the setting is wrong, ask the payer how it identified the claim as a rehab stay, and fix the bill type or provider setup that drove it.

Codes that may appear with N639

  • CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): Charges exceeded the allowed amount; N639 identifies the IRF schedule as the source.
  • PR-2 (Coinsurance Amount): Coinsurance on the rehab stay, when the plan applies it.
  • N638 (Reimbursement has been made according to the home health fee schedule.): Same idea for home health pricing.
  • N647 (Adjusted based on diagnosis-related group (DRG).): Adjustment based on a diagnosis-related group, the method many payers use for acute inpatient stays.
  • N673 (Reimbursement has been calculated based on an outpatient per diem or an outpatient factor and/or fee schedule amount.): Outpatient per diem or factor-based pricing.

N639 FAQ

Do physicians see N639?

Rarely. It relates to the facility's inpatient rehabilitation claim. Professional services during the stay are priced separately on their own fee schedule.

Why did an acute hospital claim get N639?

That suggests the payer treated the stay as an inpatient rehabilitation admission, perhaps because of the bill type, a rehab unit identifier, or the admission setup. Ask the payer how it classified the claim and correct any billing data that caused it.

Can the allowed amount be appealed?

The schedule itself usually cannot be, but how it was applied can. If the payer used the wrong rate, patient classification, or dates, request reconsideration with the supporting details.