Medical Claim Denial Codes, Explained in Plain English
What is a CARC code? A Claim Adjustment Reason Code (CARC) is a standardized code an insurer puts on an Explanation of Benefits to say why it did not pay part of a claim. A Remittance Advice Remark Code (RARC) sits alongside it and adds the specific detail behind that decision. Every CARC and RARC on this page is rewritten in plain English, with what to do next.
When an insurance company denies, reduces, or adjusts a medical claim, it doesn't explain itself in sentences — it uses these codes. Together they're the fine print of your Explanation of Benefits.
CARC vs RARC: what's the difference?
| CARC — Claim Adjustment Reason Code | RARC — Remittance Advice Remark Code | |
|---|---|---|
| What it tells you | Why an amount was not paid | The specific detail behind that reason |
| Format | A group prefix plus a number — CO-45, PR-1, OA-23 | A letter plus a number — N130, M51, MA04 |
| Can it stand alone? | Yes — every adjusted line carries at least one | No — it always accompanies a CARC |
| Does it say who pays? | Yes, through the prefix | No |
Why the prefix matters more than the number
CARC numbers arrive glued to a group prefix, and the prefix is what decides who owes the money. The same underlying reason 45 can appear as CO-45 (contractual obligation — the provider writes the amount off, and you usually should not be billed for it) or PR-45 (patient responsibility — the amount is yours). Reading only the number tells you why; reading the prefix tells you whether the bill in your hand is even correct.
Several codes can also appear on a single claim line, and only reading them together tells the full story. If a code on your document isn't listed here, or the explanation doesn't match your situation, call your insurer and ask them to explain the specific denial — codes can be applied in error, and you have the right to ask.
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Claim Adjustment Reason Codes (CARC)
115 adjustment reason codes, each with a plain-English explanation and a suggested next step.
1This amount is your deductible — the part you pay before insurance starts covering costs.
2This amount is your coinsurance — your percentage share of the cost.
3This amount is your copay — a fixed fee for the visit or service.
4The procedure code doesn't match a required modifier, or the modifier is missing/invalid.
16The claim is missing information or has an error that must be fixed before it can be processed.
18This looks like a duplicate of a claim already submitted.
22Another insurance should be billed first (you may have primary coverage elsewhere).
23Payment was affected by a prior payer's decision (coordination of benefits).
27Coverage had ended when this service was provided.
29The claim was submitted too late (past the filing deadline).
45The charge was above the maximum allowed amount, and the excess was written off.
50The insurer decided this service was not medically necessary.
55The service is considered experimental or investigational by the plan.
96This service is not covered by your plan.
97This service is already included (bundled) in the payment for another service, so it isn't paid separately.
109This claim was sent to the wrong insurer or plan.
119A benefit maximum or limit for this service has been reached.
197Pre-authorization or pre-certification was required but not obtained.
204This service isn't covered under your current benefit plan.
252Additional documentation is needed to process the claim.
5The procedure code doesn't match the place where the service was given.
6The procedure code doesn't match the patient's age.
7The procedure code doesn't match the patient's sex.
8The procedure code doesn't match the provider's specialty.
9The diagnosis doesn't match the patient's age.
11The diagnosis doesn't match the procedure that was billed.
13The date of service is after the patient's date of death on record.
15The authorization number is missing, invalid, or doesn't apply to this service.
19This is treated as a work-injury claim, so workers' compensation should be billed.
20This is treated as an auto-accident claim, so auto insurance should be billed.
21This is treated as another party's liability (someone else's insurance).
24Charges are covered under a capitation or managed-care arrangement.
26Expenses were incurred before your coverage started.
31The patient couldn't be identified as covered by this insurer.
35You've reached the lifetime benefit maximum for this service.
39Authorization was requested but denied for this service.
40This was billed as urgent/emergency care but wasn't approved as such.
44The charge was reduced because it was above the plan's fee schedule.
49This is a routine or preventive service the plan doesn't cover this way.
53Services by this type of provider aren't covered under the plan.
54Charges from multiple physicians for the same care were reduced.
58The service should have been given in a different, approved setting.
59Charges were adjusted based on multiple or concurrent procedure rules.
76Payment was already made for this service under another claim.
77This is a covered service, but the charge is the patient's responsibility.
94Payment made was more than the charge, creating a credit.
95The provider billed in a way that doesn't follow the plan's rules.
100Payment was made to the patient or another party, not the provider.
101A predetermination (pre-check of benefits) was already given.
102A major medical adjustment was applied.
104A managed-care withholding was applied to the payment.
107A related service or claim is required but wasn't found.
108Adjusted under a rental/purchase rule for equipment.
110The billing date comes before the service date.
111This provider isn't certified or eligible to be paid for this service.
114This procedure or service isn't covered when done at home.
115The procedure was postponed, canceled, or delayed.
116A pre-treatment estimate was given; this shows what would be covered.
117Transportation is only covered to the nearest appropriate facility.
118Charges were reduced for a specific health program requirement.
121An outstanding balance from a previous period was applied.
122This is a non-covered charge because it's a routine/screening exam.
125The claim was submitted with an error in how it was set up.
128Newborn services must be billed under the mother's or baby's own coverage.
129Prior processing information for this claim is incorrect.
130A claim submission fee was applied.
131A negotiated or contractual discount was applied.
132A prearranged demonstration-project adjustment was applied.
133The service is still under review (not final).
136The claim failed a required 'present on admission' indicator check.
137A regulatory penalty or fee was applied.
139Contracted funding limits for this service have been reached.
140The patient/insured health-ID number and name don't match.
142The claim was adjusted under a monthly Medicaid patient-liability rule.
146The diagnosis was invalid for the date(s) of service.
147The provider's contracted fee for this service was applied.
149The lifetime benefit maximum for this provider/service was reached.
150The information submitted doesn't support this level of service.
151The information submitted doesn't support this many services.
152The information submitted doesn't support this length of service.
167This diagnosis isn't covered by the plan.
170Payment is denied when done by this type of provider.
181The procedure code was invalid on the date of service.
182The procedure modifier was invalid on the date of service.
183The referring provider isn't eligible to refer this service.
185The rendering provider isn't eligible to perform this service.
186A level-of-care change adjustment was applied.
187This relates to a consumer-spending-account (like an HSA/FSA) payment.
188This product/procedure is only covered when used with another service.
189A not-otherwise-classified code was used when a specific code exists.
192A non-standard adjustment was applied by the plan.
193The original claim was rejected or denied for a coverage reason.
198Pre-authorization was over the approved limit or number of visits.
199A revenue code and procedure code don't match.
200Expenses were incurred during a lapse in coverage.
201This amount is the patient's responsibility under a workers' comp rule.
222This exceeds the contracted maximum number of hours/days/units.
223A mandated federal/state adjustment was applied.
225A penalty was applied for not using electronic funds transfer.
226The information requested from the provider wasn't received or was incomplete.
227Information requested from the patient wasn't received.
231This service isn't paid separately when done on the same day as another.
234This procedure isn't paid separately.
236This code combination isn't allowed together under coding rules.
237A legislatively mandated fee reduction was applied.
242Services weren't provided by network or approved providers.
243Services aren't authorized by network or plan providers.
246This service isn't payable per a payer's review decision.
251The attachment or documentation needed to process this is missing.
253A federal sequestration (across-the-board) reduction was applied.
256This service isn't payable under a managed-care contract.
272Coverage/program guidelines weren't met.
273Coverage or program limits have been exceeded.
288A referral is required but was not provided.
295The prior authorization on file doesn't match this claim.
Remittance Advice Remark Codes (RARC)
56 remark codes — the supporting detail that appears next to a CARC on your EOB.
N130Check your plan documents for coverage details on this service.
N30The patient wasn't eligible for this service under the plan at that time.
N130XCoverage or benefit details apply — review your plan.
MA04Secondary insurance info was missing or incomplete, so it couldn't be processed.
M76The diagnosis information was missing or incomplete.
M15Separately billed services are included in the main service's payment.
N522This is a duplicate of a service already submitted.
N479The Explanation of Benefits from the primary insurer is missing.
N1You may be able to appeal this decision — see your plan's appeal rights.
N4Missing or incomplete information about other insurance is holding up the claim.
N19A dependent procedure code was billed without its required primary code.
N56The procedure code billed was not correct for the service described.
N65The procedure or service isn't payable in this place of service.
N88This service is included in the payment for the main procedure.
N95This provider type can't be paid for this particular service.
N115The decision was based on a local coverage policy (LCD).
N180This item or service doesn't meet the criteria for coverage.
N210You may appeal this decision.
N265The ordering provider's ID (NPI) is missing or invalid.
N286The referring provider's ID (NPI) is missing or invalid.
N290The rendering provider's ID (NPI) is missing or invalid.
N347Your Medicare coverage for this item/service has a frequency limit.
N356This service isn't covered when it's part of routine or screening care.
N362The number of days or units billed is more than usually allowed.
N381There's a contract-specific reason for this adjustment.
N386The decision was based on a national coverage policy (NCD).
N418The claim was sent to the wrong payer or contractor.
N435This exceeds the outpatient limit for a benefit period.
N448This drug or service isn't on the plan's approved list (formulary).
N523The number of services billed is more than the allowed maximum.
N598The primary insurer's payment information is needed.
N620This procedure needs a matching diagnosis to be covered.
N640This charge exceeds the covered amount for the service.
N657This should have been billed with a more specific code.
M16Refer to the payer's bulletin or notice for more details.
M25The information doesn't support the need for this service.
M38This service requires prior authorization that wasn't obtained.
M39This service isn't covered because it's considered routine.
M51The procedure code is missing, incomplete, or invalid.
M77The place of service is missing, incomplete, or invalid.
M79The charge amount is missing, incomplete, or invalid.
M80This service can't be paid on the same day as a related service.
M81A required diagnosis code is missing.
M119The drug (NDC) code is missing, incomplete, or invalid.
M123The drug name, strength, or quantity information is missing.
MA01You have the right to appeal this Medicare decision.
MA13You may be responsible for a portion under a specific program rule.
MA15Your claim was split for processing.
MA18This claim was also forwarded to your secondary insurer.
MA27Your Medicare ID number is missing, incomplete, or invalid.
MA130The claim has a missing or invalid field and can't be processed as is.
N425This is a statutorily excluded service (not covered by law).
N517A resubmission is required with corrected information.
N575The name on the claim doesn't match the insurer's records.
N700A required modifier for this service is missing.
N702The decision was based on review of prior claims for this patient.
Frequently asked questions about denial codes
What is a CARC code?
A Claim Adjustment Reason Code (CARC) is a standardized code an insurer puts on an Explanation of Benefits to say why it did not pay part of a claim. It always carries a group prefix — CO, PR or OA — and that prefix, not the number, is what decides who is expected to pay the amount.
What is the difference between a CARC and a RARC code?
A CARC states the reason an amount was adjusted and who is responsible for it. A RARC (Remittance Advice Remark Code) adds the specific detail behind that reason and never appears on its own — it always accompanies a CARC.
Does a denial code mean I have to pay the bill?
Not on its own. A CO prefix means the provider agreed by contract to write the amount off, so it usually should not be billed to you at all. A PR prefix means the amount is patient responsibility. If a provider bills you for an amount your EOB marked CO, that is worth questioning before you pay.
Where do I find denial codes on my EOB?
They appear next to each claim line, usually in a column labelled reason code, adjustment code, or remark code. One line can carry several codes at once, and only reading them together gives the full picture.
Related guides
- Medical Bill vs EOB: What Is the Difference?
- How to Dispute a Medical Bill — Find Billing Errors Before You Pay
- What Is an Itemized Medical Bill? How to Request One
- Medical procedure codes (CPT & HCPCS) explained — the codes for what was done, as opposed to why it wasn't paid