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The 49 reason and remark codes behavioral health facilities see most, in plain English. Each one shows the typical cause and the first fix. Runs in your browser; nothing is sent.

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49 codes

CO-27
Claim adjustment reason code
Recoverable: sometimes
The date of service falls after the patient's coverage ended.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Coverage lapsed during a long residential stay, or the patient lost employer coverage and COBRA was not yet elected.
First fix: Eligibility check
Run a fresh eligibility check for each date. If COBRA is elected it can reinstate coverage back to the loss date; rebill once active. Otherwise bill the right payer.
More on CO-27
CO-26
Claim adjustment reason code
Recoverable: sometimes
The date of service falls before the patient's coverage started.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Admission came before a new plan's effective date, or retroactive enrollment has not posted.
First fix: Eligibility check
Confirm effective dates with the plan. Bill the prior payer for earlier days, or rebill after retro enrollment posts.
CO-31
Claim adjustment reason code
Recoverable: usually
The payer cannot match the patient to one of its members.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Wrong member ID, a name or birth date mismatch, or a missing dependent suffix entered at a rushed admission.
First fix: Corrected claim
Verify demographics against an eligibility response (270/271) and the card, then send a corrected claim.
CO-177
Claim adjustment reason code
Recoverable: rarely
The patient did not meet the plan's eligibility requirements for this service.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Plan waiting periods or program rules the patient did not meet on the date of service.
First fix: Eligibility check
Read the plan rule cited. If the patient did qualify, appeal with proof; if not, find the right payer.
CO-197
Claim adjustment reason code
Recoverable: sometimes
No precertification, authorization or notification was on file.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Admission or a step-down to PHP or IOP went ahead without an approved authorization, or the auth sits under the wrong level of care.
First fix: Authorization request
Search your auth records first. If you had one, send a corrected claim with the number. If not, ask about retro review, and appeal if emergency or urgent admission rules apply.
More on CO-197
CO-198
Claim adjustment reason code
Recoverable: sometimes
Services went beyond what was authorized.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
More residential or PHP days billed than approved, often after a concurrent review was missed.
First fix: Appeal
Request the added days with clinical notes. If denied, appeal with the record for each extra day.
CO-15
Claim adjustment reason code
Recoverable: usually
The authorization number was missing, invalid, or did not fit the service or provider.
X12 deactivated this code in 2018. Current remits use CO-197, CO-284 or CO-296, but older systems still show it.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Auth number left off the UB-04, or an auth for a different level of care.
First fix: Corrected claim
Add the correct authorization number on a corrected claim.
CO-284
Claim adjustment reason code
Recoverable: usually
The authorization number may be valid but does not apply to the services billed.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
The auth covers IOP but the claim billed PHP, or the dates fall outside the approved span.
First fix: Corrected claim
Match revenue codes, HCPCS and dates to the auth. Correct the claim, or get the right auth for what was given.
CO-50
Claim adjustment reason code
Recoverable: sometimes
The payer decided the service was not medically necessary.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Residential, PHP or IOP days denied at concurrent or retrospective review, often against proprietary criteria.
First fix: Appeal
Appeal with records matched to the criteria the payer named, plus a physician letter. Ask for a peer-to-peer. The member can take it to external review.
More on CO-50
CO-150
Claim adjustment reason code
Recoverable: sometimes
The payer says the records do not support the level of service billed.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
PHP billed but notes show IOP hours, or notes do not show the intensity of the level billed.
First fix: Appeal
If notes support the level, appeal with them. If they match a lower level, correct the claim.
CO-151
Claim adjustment reason code
Recoverable: sometimes
The payer says the records do not support this many services or this frequency.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Units on IOP or PHP lines exceed what the auth or notes support.
First fix: Appeal
Compare units to the auth and the notes. Correct the units, or appeal with documentation.
CO-152
Claim adjustment reason code
Recoverable: sometimes
The payer says the records do not support this length of service.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Residential stay ran longer than the payer approved at concurrent review.
First fix: Appeal
Appeal with day-by-day clinical evidence and the discharge plan. Ask for a peer-to-peer first.
N10
Remark code (RARC)
Recoverable: sometimes
The adjustment came from a review organization, consultant or peer review.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
A clinical reviewer cut days or the level of care.
First fix: Appeal
Ask for the reviewer's rationale and criteria, then appeal with records matched to them.
CO-16
Claim adjustment reason code
Recoverable: usually
The claim is missing information or has a billing error. A remark code says what.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Missing attending NPI, wrong type of bill, or a missing HCPCS on a revenue code line.
First fix: Corrected claim
Read the paired remark code, fix that field and send a corrected claim. Do not appeal.
More on CO-16
CO-4
Claim adjustment reason code
Recoverable: usually
The modifier does not fit the procedure code, or a required modifier is missing.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
An IOP or PHP HCPCS sent without the modifier the payer's guide or contract requires.
First fix: Corrected claim
Add or fix the modifier per the payer's billing guide and resubmit as a corrected claim.
More on CO-4
CO-11
Claim adjustment reason code
Recoverable: usually
The diagnosis does not fit the procedure billed.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
SUD level of care billed with only a mental health diagnosis, or diagnosis order that puts the wrong one first.
First fix: Corrected claim
Check the chart. If coding was wrong, send a corrected claim; if right, appeal with records.
CO-97
Claim adjustment reason code
Recoverable: sometimes
Payment for this service is included in another service already paid.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Labs, therapy or room and board billed on separate lines when the per diem already includes them.
First fix: Review only
Check what your contract's per diem includes. If the line is separately payable, appeal with the contract language.
CO-181
Claim adjustment reason code
Recoverable: usually
The procedure code was not valid on the date of service.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
A deleted or not yet effective HCPCS code, often from an old charge master.
First fix: Corrected claim
Update the code to one valid on that date and resubmit.
CO-58
Claim adjustment reason code
Recoverable: usually
The payer says the service was given in the wrong or an invalid place of service.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Type of bill or place of service does not match the level of care billed.
First fix: Corrected claim
Check type of bill, revenue codes and facility setup, then correct the claim.
M51
Remark code (RARC)
Recoverable: usually
Procedure code missing, incomplete or invalid.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Revenue code line sent without the HCPCS the payer requires, such as H0015 with 0906.
First fix: Corrected claim
Add the HCPCS the payer's guide pairs with that revenue code and resubmit.
N290
Remark code (RARC)
Recoverable: usually
The rendering or attending provider's primary identifier is missing or invalid.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Attending clinician NPI missing, or an individual NPI where the payer expects another.
First fix: Corrected claim
Add the correct NPI for the attending or rendering provider and resubmit.
MA130
Remark code (RARC)
Recoverable: usually
The claim had incomplete or invalid information and could not be processed, so there are no appeal rights. Submit a new claim.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Front-end data errors on the claim.
First fix: Corrected claim
Fix the data and send a new claim. An appeal will not work for an unprocessable claim.
OA-18
Claim adjustment reason code
Recoverable: rarely
The claim or line is an exact duplicate of one already received.
If it is truly a duplicate, there is nothing to recover. If it was a correction sent wrong, resend it correctly.
Group OA: Other adjustment
An adjustment that is neither the provider's nor the patient's, such as a prior payer's payment or an exact duplicate.
Typical behavioral health cause
A claim resent as new instead of as a corrected claim, or interim bills resent with overlapping dates.
First fix: Review only
Check claim status. To change a claim, send frequency code 7 with the original claim number.
CO-29
Claim adjustment reason code
Recoverable: rarely
The deadline for filing the claim has passed.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Claims held waiting for auth, or rejected at the clearinghouse and never fixed.
First fix: Appeal
Appeal only with proof you filed on time, such as a clearinghouse acceptance report or payer acknowledgment (277CA).
More on CO-29
CO-22
Claim adjustment reason code
Recoverable: usually
Another payer may be primary under coordination of benefits.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
The patient has two plans, or the payer's COB record is out of date.
First fix: Eligibility check
Ask the patient to update COB with the plan. Bill the primary, then the secondary with the primary's remittance.
OA-23
Claim adjustment reason code
Not a denial
The adjustment reflects what a prior payer paid or adjusted.
Group OA: Other adjustment
An adjustment that is neither the provider's nor the patient's, such as a prior payer's payment or an exact duplicate.
Typical behavioral health cause
Normal on secondary claims.
First fix: Review only
Check the math against the primary remittance. No action if it ties out.
N479
Remark code (RARC)
Recoverable: usually
The other payer's explanation of benefits is missing.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Secondary claim sent without the primary payer's payment details.
First fix: Corrected claim
Send the secondary claim with the primary payer's adjudication, electronically or with the EOB attached.
MA04
Remark code (RARC)
Recoverable: usually
The secondary payer needs the primary payer's identity or payment information.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Primary payer data left off the secondary claim.
First fix: Corrected claim
Add the primary payer loop and amounts and resubmit.
CO-109
Claim adjustment reason code
Recoverable: usually
This payer does not cover the claim. Send it to the correct payer.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Behavioral health is carved out to another company (such as Optum Behavioral Health, Evernorth or Carelon), or a Blue claim went to the wrong host plan.
First fix: Rebill correct payer
Check the member card for the behavioral health administrator and payer ID, then bill that payer.
PR-1
Claim adjustment reason code
Not a denial
Amount applied to the patient's deductible.
Group PR: Patient responsibility
The patient owes the amount, such as a deductible, coinsurance or copay.
Typical behavioral health cause
Normal early in a plan year, and large on high-deductible plans with residential stays.
First fix: Bill patient
Not a denial. Confirm the amount, then follow your financial policy for the patient balance.
More on PR-1
PR-2
Claim adjustment reason code
Not a denial
The patient's coinsurance share.
Group PR: Patient responsibility
The patient owes the amount, such as a deductible, coinsurance or copay.
Typical behavioral health cause
Normal cost sharing; often higher out of network.
First fix: Bill patient
Not a denial. Verify the percentage against benefits, then bill per your policy.
PR-3
Claim adjustment reason code
Not a denial
The patient's copay.
Group PR: Patient responsibility
The patient owes the amount, such as a deductible, coinsurance or copay.
Typical behavioral health cause
Normal cost sharing per visit or day.
First fix: Bill patient
Not a denial. Collect per your policy.
CO-45
Claim adjustment reason code
Not a denial
The charge is more than the fee schedule or contracted amount allows.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Normal contractual write-off in network. Out of network, it reflects the plan's allowed amount method.
First fix: Review only
Compare the allowed amount to your contract. If underpaid, file a payment dispute. Do not bill the patient for a CO amount.
CO-96
Claim adjustment reason code
Recoverable: sometimes
The charges are not covered. A remark code gives the reason.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Plan excludes the level of care, out-of-network benefits, or a specific service.
First fix: Review only
Read the remark code and the plan's benefits. If an exclusion may conflict with parity rules, ask whether an appeal applies.
More on CO-96
CO-204
Claim adjustment reason code
Recoverable: rarely
The service is not covered under the patient's current benefit plan.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
A plan that excludes residential treatment or a specific program type.
First fix: Appeal
Check the plan document. Appeal only if the exclusion conflicts with the plan or with parity rules.
CO-119
Claim adjustment reason code
Recoverable: rarely
The benefit maximum for the period has been reached.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Day or visit limits on behavioral health benefits.
First fix: Appeal
Verify the limit. If it is stricter than the plan's medical limits, ask whether a parity appeal applies.
CO-167
Claim adjustment reason code
Recoverable: sometimes
The diagnosis is not covered.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
An excluded or unspecified diagnosis code listed first.
First fix: Corrected claim
Check diagnosis specificity and order. Correct the claim, or appeal if the diagnosis is right.
N130
Remark code (RARC)
Recoverable: sometimes
Check the plan's benefit documents for limits on this service.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
A plan limit or exclusion applied.
First fix: Review only
Get the plan's benefit language before you decide to appeal.
CO-185
Claim adjustment reason code
Recoverable: sometimes
The rendering provider is not eligible to perform the service billed.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
The attending clinician is not credentialed with the plan, or the credential does not cover this service.
First fix: Credentialing
Check credentialing. Correct the attending provider, or finish credentialing and rebill.
CO-170
Claim adjustment reason code
Recoverable: sometimes
Payment is denied when billed by this type of provider.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Facility taxonomy does not match the level of care billed.
First fix: Credentialing
Check the taxonomy and licensure on file with the payer, then correct the claim.
CO-171
Claim adjustment reason code
Recoverable: sometimes
Payment is denied when this type of provider bills in this type of facility.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Level of care billed under a facility setup the payer does not recognize for it.
First fix: Credentialing
Confirm the facility is contracted and licensed for that level, then correct the claim.
CO-B7
Claim adjustment reason code
Recoverable: sometimes
The provider was not certified or eligible to be paid for this service on this date.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
A license, accreditation or credential took effect after the admission date.
First fix: Credentialing
Send proof of the license or credential dates. Rebill once the payer updates its file.
CO-242
Claim adjustment reason code
Recoverable: rarely
The services were not given by a network provider.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Out-of-network facility on an HMO or EPO plan with no out-of-network benefit.
First fix: Appeal
Ask about a network gap exception or single case agreement. Appeal if no in-network option was available.
CO-252
Claim adjustment reason code
Recoverable: usually
The payer needs an attachment or other documentation to decide the claim.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
Payer wants the treatment plan, progress notes or the physician order.
First fix: Records
Send the records tied to the claim (an electronic 275 attachment where the payer supports it, or its portal).
CO-226
Claim adjustment reason code
Recoverable: usually
Information the payer asked the provider for was not sent, was late, or was incomplete.
Group CO: Contractual obligation
The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Typical behavioral health cause
A records request letter went unanswered.
First fix: Records
Send the complete records and ask the payer to reopen the claim.
M127
Remark code (RARC)
Recoverable: usually
The patient's medical record for this service is missing.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Payer asked for records for a residential or PHP stay.
First fix: Records
Send the records for the billed dates, referencing the claim number.
N54
Remark code (RARC)
Recoverable: usually
The claim does not match the services that were authorized.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Billed level, dates or units differ from the authorization.
First fix: Corrected claim
Line up the claim with the auth, or get the auth updated for what was given.
N362
Remark code (RARC)
Recoverable: sometimes
The days or units billed exceed the payer's maximum.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
More days billed than authorized or allowed.
First fix: Appeal
Check units against the auth. Correct them, or appeal with notes for the added days.
N386
Remark code (RARC)
Recoverable: rarely
The decision was based on a Medicare National Coverage Determination.
How it is used
Remark codes explain a reason code. Read them together.
Typical behavioral health cause
Seen on Medicare Advantage claims, not commercial ones.
First fix: Review only
Read the cited NCD. Medicare Advantage appeal rules apply.

Educational summary, not billing advice. Meanings are our own short paraphrases. Official descriptions are at x12.org (reason codes) and x12.org (remark codes). "Recoverable" is our general read of how often a denial can be fixed or overturned, not a measured rate. Code lists checked October 2026.

Group codes

Every reason code on a remit comes with a group code that says who carries the amount.

CO Contractual obligation: The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
PR Patient responsibility: The patient owes the amount, such as a deductible, coinsurance or copay.
OA Other adjustment: An adjustment that is neither the provider's nor the patient's, such as a prior payer's payment or an exact duplicate.
PI Payer initiated reduction: The payer reduced the amount for a reason it believes is not the patient's responsibility, outside a contract.

Questions

What is a CARC?

A claim adjustment reason code. It tells you why a payer paid a claim or line differently than billed. X12 maintains the official list.

What is a RARC?

A remittance advice remark code. It adds detail to a reason code, for example which field was missing.

What do CO, PR, OA and PI mean?

They are group codes. CO is contractual obligation, PR is patient responsibility, OA is other adjustment and PI is payer initiated reduction.

Next steps

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