Common Denial Codes in Medical Billing (2026)

Common denial codes in medical billing are standardized numeric identifiers that explain why a claim was not paid as submitted.

Knowing what each code means, and what action it requires, is the difference between recovered revenue and written-off claims.

According to Optum’s denial rate analysis, the average healthcare organization faces a 12% claim denial rate with 84% of those denials avoidable and 22% unrecoverable once missed. That is revenue walking out the door on claims that could have been paid the first time.

Let’s look into:

• Common medical billing denial codes and their meanings
• Appeals vs. corrected claims vs. resubmissions
• CARCs, RARCs, and group codes explained
• Denial causes and how to fix them
• Denial prevention best practices

TLDR:  The most common medical billing denial codes

The most common medical billing denial codes are CO-16, CO-18, CO-22, CO-29, CO-50, CO-96, CO-97, CO-109, CO-197, PR-1, PR-2, PR-3, and PR-27. Each maps to a specific operational failure and requires a distinct corrective action.

A denial code, formally a Claim Adjustment Reason Code (CARC), is a standardized numeric identifier attached to a claim adjustment on remittance advice. It tells the provider why payment was reduced, denied, or adjusted. Below are the 13 most common codes your team will encounter.

Code	Plain-English Meaning	Common Cause	First Action
CO-16	Claim lacks information needed for adjudication	Missing NPI, modifier, or diagnosis	Read RARC; correct and resubmit
CO-18	Exact duplicate claim or service	Resubmission of unpaid claim without status check	Check claim status (276/277); hold resubmit
CO-22	This care may be covered by another payer	Primary payer not billed first (COB issue)	Verify payer order; obtain primary EOB
CO-29	Time limit for filing expired	Claim submitted after payer deadline	Appeal with proof of timely filing
CO-50	Non-covered service, not deemed medically necessary	Diagnosis does not support procedure per LCD	Review LCD; improve documentation or appeal
CO-96	Non-covered charge(s)	Service excluded under benefit plan	Verify coverage; bill patient if PR applies
CO-97	Payment included in allowance for another service	E/M bundled into procedure; missing modifier -25	Add modifier -25 with documentation support
CO-109	Claim not covered by this payer	Wrong payer billed	Identify correct payer; resubmit
CO-197	Precertification/authorization absent	Service rendered without prior authorization	Appeal for retro-auth or exception
PR-1	Deductible amount	Patient’s annual deductible not met	Bill patient per contract
PR-2	Coinsurance amount	Patient cost-share responsibility	Bill patient per contract
PR-3	Co-payment amount	Fixed patient payment due at service	Collect at point of service
PR-27	Expenses incurred after coverage terminated	Patient’s insurance inactive on date of service	Verify eligibility; bill patient or pursue secondary

Handling always depends on the group code, RARC, and individual payer policy. Never act on the CARC alone.

How denial codes work – CARC, RARC, and group codes explained

Every denial on a remittance advice (ERA/835 transaction) is built from three layers — the Group Code (who is financially responsible), the CARC (why the payment changed), and the RARC (the specific detail needed to act).

Group Code	Full Name	Financial Responsibility	Billable to Patient?
CO	Contractual Obligation	Provider	No – contractual write-off
PR	Patient Responsibility	Patient	Yes – per contract terms
OA	Other Adjustment	Neither / Other	Depends on payer
PI	Payer Initiated	Payer	No

Common denial codes by Cause and how to fix Them

Denial codes are easier to fix and prevent when grouped by operational cause rather than by code number. 

The categories below including missing information, duplicates, COB errors, timely filing, eligibility, authorization, medical necessity, bundling, patient responsibility, and credentialing cover the vast majority of what billing teams encounter daily.

The framework below mirrors Optum’s denial category breakdown, which attributes 24% of denials to eligibility/registration issues and 16% to missing or invalid claim data.

Missing or incomplete information denials – CO-16, CO-252

CO-16 is the most frequently triggered medical billing denial code. It is a catch-all that always requires a RARC to identify what is actually missing. Without reading the RARC, there is no actionable path forward.

CO-252 is the complementary code indicating that an additional service was submitted without required documentation.

Code	Meaning	First Action
CO-16	Claim/service lacks info needed for adjudication	Read RARC immediately; correct the specific missing element
CO-252	Service not payable without supporting documentation	Attach clinical notes, orders, or supporting records; resubmit

For example, a claim is submitted for a specialist visit. CO-16 fires with RARC MA61 (missing/incomplete/invalid Social Security Number).

The fix is to correct the patient demographic field and resubmit as a corrected claim, not a new claim.

Note that Experian Health reports that 68% of providers cite intake data errors as a leading denial cause. Front-end claim edits and clearinghouse scrubbing before submission eliminate most CO-16 triggers.

Duplicate claim denials – CO-18

A denial code CO-18 fires when the payer identifies the submission as an exact duplicate of a previously received claim. But not all CO-18s are true duplicates.

Scenario	What Happened	Correct Response
True duplicate	Same claim submitted twice without status check	Check 276/277 claim status; do not resubmit
False duplicate	Corrected claim submitted but not flagged as corrected	Resubmit as a corrected claim (frequency code 7 or 8)
Voided claim resubmission	Original voided but new claim assigned same ICN by payer	Contact payer to confirm void was processed

Always check claim status via 276/277 transaction before resubmitting any unpaid claim.

Most clearinghouses provide real-time status. Do not assume non-payment means non-receipt.

Coordination of benefits and wrong-payer denials – CO-22, OA-23, CO-109

These three codes all indicate a payer order or coverage mismatch. They represent a large share of the 24% of denials Optum attributes to eligibility and registration errors.

Code	Meaning	Next Step
CO-22	This care may be covered by another payer per COB	Verify primary payer; obtain primary EOB; resubmit with COB data
OA-23	Payment adjusted due to payer’s COB rules	Review payer COB policy; check primary payment amount
CO-109	Claim not covered by this payer/contractor	Identify correct payer; resubmit to correct entity

The workflow is:

Timely filing denials – CO-29

A denial code CO-29 means the claim was submitted after the payer’s filing deadline.

Payer-specific deadlines range from 90 days (some commercial plans) to 12 months (most Medicare). Deadlines run from the date of service, not the billing date.

Payer Type	Typical Filing Limit	Notes
Medicare	12 months from date of service	CMS Publication 100-04, Ch. 1
Medicaid	Varies by state (90 days to 12 months)	Check state-specific provider manual
Commercial	90 to 180 days (varies by contract)	Check payer contract or provider manual
Workers’ Comp	Varies by state law	Statutory, not contractual

Appeal checklist for CO-29:

• Clearinghouse acknowledgment report confirming original transmission date
• Proof of timely submission, batch confirmation or 999/TA1 acknowledgment
• Any corrected claim history showing original submission reference number
• Payer-specific appeal form, if required

Track filing deadlines by payer in your practice management system. Set automated alerts at 30, 60, and 80 days post-service for unpaid claims.

Eligibility and coverage denials – PR-27, CO-96, CO-204, PR-204

These codes indicate that the service was not covered because of the patient’s benefit plan status on the date of service.

Code	Meaning	Resolution Path
PR-27	Expenses incurred after coverage terminated	Bill patient; check for secondary coverage; verify retroactive termination rules
CO-96	Non-covered charge(s) – plan exclusion	Verify benefit plan; check if billable to patient under PR group code
CO-204	Service not covered by this payer/contractor	Check payer coverage policy; refer patient to correct plan
PR-204	Service not covered, patient responsible	Bill patient; ensure signed ABN (Medicare) or non-covered service acknowledgment

The single most effective denial prevention step for this category is eligibility verification before every date of service – ideally 48 to 72 hours in advance.

Real-time 270/271 eligibility checks through your clearinghouse catch inactive coverage, incorrect payer order, and plan exclusions before a claim is ever generated.

Authorization and referral denials – CO-197, CO-15, CO-284, CO-296

Authorization denials are among the most impactful in terms of dollar value and staff burden. The AMA reports that 93% of physicians report care delays attributable to prior authorization requirements. Yet according to KFF data, 80.7% of appealed Medicare Advantage denials are overturned – while only 11.5% of denials are ever appealed.

Code	Meaning	Resolution
CO-197	Precertification/authorization absent or exceeded	Appeal for retro-auth (if payer policy allows); request exception
CO-15	Payment adjusted because authorization number was missing, invalid, or does not apply to billed service	Verify auth number; resubmit with correct authorization reference
CO-284	Authorization number does not apply to rendered service	Confirm authorization covers exact CPT/HCPCS billed
CO-296	Authorization does not apply to rendering provider	Confirm provider is listed on authorization; request amendment if needed

Implement an authorization tracker that ties each auth number to a specific CPT, provider, and date range.

Real-time auth status checks through your payer portals or a CAQH-estimated $515M in annual savings from electronic prior authorization is achievable when the workflow is automated.

Medical necessity and diagnosis mismatch denials – CO-50, CO-11, CO-150, CO-151, CO-167

These codes fire when documentation fails to support the medical necessity of the billed service, or when the submitted ICD-10 code does not support the procedure under the payer’s Local Coverage Determination (LCD) or National Coverage Determination (NCD). 

The CMS FY2023 Improper Payment Report cites a 7.66% improper payment rate, with documentation and medical necessity errors as the primary root causes.

Code	Meaning	Fix
CO-50	Non-covered –  not medically necessary per payer criteria	Review LCD/NCD; strengthen clinical documentation; appeal with additional records
CO-11	Diagnosis inconsistent with procedure	Correct ICD-10 code to one that supports CPT; re-evaluate code pairing
CO-150	Payment adjusted because payer deems information inappropriate	Review submission data; provide clinical notes on appeal
CO-151	Payment adjusted because payer deems quantity inappropriate	Review quantity billed against documentation; appeal with clinical rationale
CO-167	Diagnosis not covered by payer	Verify diagnosis is billable under this payer’s plan; check plan exclusions

For example, a provider bills CPT 93306 (echocardiogram with Doppler).

The ICD-10 submitted is Z00.00 (routine exam). The payer’s LCD requires a cardiac diagnosis to support the echocardiogram. CO-50 fires.

The fix is to review the clinical record for a supporting diagnosis (e.g., I10 hypertension, I25.10 CAD), amend the coding to reflect the documented condition, and resubmit with the corrected claim.

Always review the payer’s LCD before appealing a CO-50. An appeal without LCD alignment will not succeed.

Bundling, modifier, and NCCI edit denials – CO-97, CO-4, CO-236

These codes relate to how multiple services are billed together – and whether the combination is payable under National Correct Coding Initiative (NCCI) edits.

Code	Meaning	Resolution
CO-97	Service included in the allowance for another service	Check if modifier -25 or -59 is appropriate; add modifier with documentation
CO-4	Service inconsistent with modifier used	Verify modifier selection; ensure documentation supports modifier use
CO-236	Procedure/modifier combination conflicts with NCCI edit	Review NCCI edits for the CPT pair; append correct modifier with documentation

Modifier -25 is required when a significant, separately identifiable E/M service is performed on the same day as a procedure. Modifier -59 indicates a distinct procedural service that would otherwise be bundled. 

Both modifiers require corresponding documentation in the medical record. Do not append modifiers as a default denial override – append them only when the clinical scenario genuinely supports it.

The X12 definition of code 97 specifies that this adjustment is used when a service is already included in the global package of another billed procedure.

Patient responsibility adjustments – PR-1, PR-2, PR-3, PR-96, PR-119, PR-204

The PR denial code group is often misread as a denial. These are adjustments – not payer rejections. They indicate the portion of the claim being assigned to the patient.

Code	Description	Action
PR-1	Deductible amount	Bill patient; track deductible applied year-to-date
PR-2	Coinsurance amount	Bill patient per payer explanation
PR-3	Co-payment amount	Collect at point of service; post if collected
PR-96	Non-covered charge(s) – patient responsible	Bill patient; ensure patient signed a non-covered service notice
PR-119	Benefit maximum reached	Bill patient; notify proactively at eligibility check
PR-204	Service not covered – patient responsible	Bill patient per contract; confirm patient was informed

Note that the PR codes may still be billable to the patient, but always cross-reference your payer contract.

Balance billing rules apply in many commercial and all Medicare/Medicaid contexts.

Provider enrollment and credentialing denials – CO-B7, CO-170, CO-185

These codes indicate that the rendering or billing provider was not credentialed, not enrolled, or not in a recognized status with the payer on the date of service.

Code	Meaning	Resolution
CO-B7	Provider not eligible on date of service	Verify enrollment effective date; appeal with credentialing documentation
CO-170	Payment denied – payment already made for services/procedures	Audit for duplicate provider enrollment or payment posting error
CO-185	Service not paid – provider was not certified/eligible on date of service	Confirm taxonomy code, NPI registration, and re-credentialing dates

Maintain a credentialing calendar with re-credentialing alerts 90 days before expiration. Verify that taxonomy codes match the enrolled specialty for each payer. 

Confirm NPI Type 1 (individual) and NPI Type 2 (organization) are both active and correctly linked in your billing system.

How to decide: correct, appeal, resubmit, bill patient, or write off

The correct response to a denial depends entirely on its root cause. 

Corrected claims resolve provider data errors, while appeals address incorrect payer decisions.

Patient billing applies to PR adjustments and, using the wrong path adds 30 to 60 days to resolution.

Not every denial gets the same response. Using the wrong action wastes time and can delay payment further. Use this decision table as your starting point.

Denial Situation	Correct Action	Notes
Missing or incorrect claim data (CO-16, CO-252)	Submit corrected claim	Frequency code 7 (replacement); do not appeal
Payer made wrong decision with documentation support	Appeal with documentation	https://www.kff.org
Wrong payer billed (CO-109)	Resubmit to correct payer	Confirm payer order before resubmitting
Patient deductible, copay, coinsurance (PR-1, PR-2, PR-3)	Bill patient per contract	Post payer adjustment; generate patient statement
Contractual obligation write-off (CO codes per contract)	Write off per payer contract	Do not balance bill patient for CO adjustments
Missing authorization – retro-auth available (CO-197)	Appeal for retro-authorization	Document medical necessity; submit physician attestation
Duplicate claim (CO-18 – true duplicate)	Hold; verify with claim status	Check 276/277 before any resubmission

According to KFF, only 11.5% of denied Medicare Advantage claims are appealed – despite an 80.7% overturn rate. That gap is recoverable revenue left on the table.

How to prevent the most common denials

The most impactful denial prevention steps are front-end: verify eligibility before every visit, confirm authorization before scheduling, and validate claim data before submission. 

Optum data indicates that 84% of denials are avoidable, with 44% preventable at the front end of the revenue cycle. Experian Health reports that 68% of providers cite intake data errors as a primary cause.

Common denial code examples

The six scenarios below show how common denial codes arise in real billing situations and what the correct resolution looks like:

Commonly confused denial codes

Several denial codes are routinely misapplied because they share surface-level similarities. The table below clarifies the key distinctions for the five most commonly confused pairs and identifies the correct action for each.

Codes	Key Difference	What to Check
CO-50 vs CO-96	CO-50 = payer determination of medical necessity failure; CO-96 = service is a plan exclusion regardless of necessity	CO-50: review LCD and documentation; CO-96: verify benefit plan exclusions
CO-16 vs CO-252	CO-16 = claim data missing for adjudication; CO-252 = documentation missing to support an already-submitted service	Both require RARC. CO-16: fix claim data; CO-252: attach clinical documentation
CO-22 vs OA-23	CO-22 = payer suspects another payer is primary (COB issue); OA-23 = payer adjusted because COB rules were already applied	CO-22: resubmit with correct payer order; OA-23: review primary payment amount and crossover setup
CO-15 vs CO-197	CO-197 = authorization is completely absent; CO-15 = authorization number present but invalid or mismatched	CO-197: request retro-auth; CO-15: verify and correct auth number
CO-97 vs CO-236	CO-97 = service included in global package of another billed service; CO-236 = procedure/modifier combination violates NCCI edit	CO-97: check global days and E/M modifier -25; CO-236: look up specific NCCI edit pair

Common mistakes when reading denial codes

The most costly denial-reading errors are acting on a CARC without reading the RARC, misrouting PR adjustments as denials, resubmitting without a status check, and appealing when a corrected claim is the appropriate response. Each of these mistakes delays resolution by weeks:

Where to verify denial code definitions

Authoritative sources for denial code definitions are X12.org for CARCs, the CMS RARC page for remark codes, the CMS Medicare Learning Network for Medicare-specific guidance, and the CMS NCCI Policy Manual for bundling edits.

Resource	Official URL	Purpose
CARC (Claim Adjustment Reason Codes)	https://x12.org/codes/claim-adjustment-reason-codes	Official CARC definitions (some codes require accompanying RARCs).
RARC (Remittance Advice Remark Codes)	https://www.cms.gov/medicare/coding-billing/remittance-advice-remark-codes	Official CMS remark code definitions used with CARCs.
Medicare Learning Network (MLN)	https://www.cms.gov/training-education/medicare-learning-network-mln	Medicare billing guides, transmittals, and educational resources.
CMS NCCI Policy Manual	https://www.cms.gov/medicare/medicare-fee-for-service-payment/physicianfeesched/national-correct-coding-initiative-ncci-edits	Official guidance on NCCI edits, bundling rules, and modifier usage.

Always check the individual payer’s provider manual. CARC definitions are standardized; application is not.

Stop guessing why claims are denied. Start preventing them.

Reading denial codes is only the first step.

Recovering revenue requires identifying root causes, correcting claims the right way, and preventing the same denials from recurring.

Our medical billing specialists help practices:

• Analyze denial trends by payer, provider, and code
• Reduce avoidable denials with front-end claim validation
• Manage appeals, corrected claims, and resubmissions
• Improve clean claim rates and accelerate reimbursements
• Strengthen your entire revenue cycle with ongoing denial management

Turn denial data into paid claims. Contact MedHeave today to see how our medical billing experts can help reduce denials and maximize collections.

Frequently asked questions

The questions below cover the most common points of confusion around denial codes: