Summary
Learn the top 10 medical billing denial codes in 2026 and the best appeal strategy for each. This guide explains common denial reasons, effective correction and appeal playbooks, Medicare appeal timelines, and proven denial prevention practices to improve claim reimbursement and revenue cycle performance.
Book a Free Consultation Today!Denial management consumes a significant portion of revenue cycle resources, with billing teams spending countless hours resolving the same recurring denial codes. If your practice cannot identify its most frequent denial codes by payer, it becomes much harder to understand where revenue is being lost.
This guide explains the ten denial codes that billing teams encounter most often, what each code means, and the most effective appeal strategy for handling it. Every statistic included comes from a recognized primary source. Where commonly cited industry figures cannot be verified through an original source, this guide clearly identifies them as unverified instead of presenting them as fact.
Before diving into the codes, it’s important to understand one limitation. There is no official federal dataset that ranks CARC denial codes nationally by frequency. While CMS reports denial reasons in broader categories, it does not publish CARC-level rankings linked to denied services. As a result, the codes discussed below represent those most commonly found in everyday denial queues across multiple specialties and insurance payers rather than an official national ranking.
Denial management involves much more than simply appealing rejected claims. It is the ongoing process of identifying why a payer denied payment, recovering reimbursement through corrected claims or formal appeals, and addressing the underlying operational issue to prevent similar denials in the future.
Every denial generally contains three essential components:
- A Group Code, identifying who is financially responsible.
- A Claim Adjustment Reason Code (CARC) explaining why payment changed.
- A Remittance Advice Remark Code (RARC) providing additional details and instructions when applicable.
What the denial data actually shows in 2026
Reliable denial benchmarks are more limited than many industry reports suggest. The strongest publicly available data comes from HealthCare.gov Marketplace plans, which excludes employer-sponsored insurance, Medicare, Medicaid, and state-based exchanges.
Within that dataset, the trends are still revealing. According to KFF’s analysis of CMS Transparency in Coverage data, insurers denied 19% of in-network claims and 37% of out-of-network claims during 2024. Denial rates varied dramatically by insurer, ranging from 3% to 36%, highlighting that payer mix has a much greater impact than any single national average.
| Metric | Figure | Source |
|---|---|---|
| In-network denial rate, HealthCare.gov plans, 2024 | 19% | KFF / CMS Transparency in Coverage |
| Out-of-network denial rate, same plans | 37% | KFF / CMS |
| Range across reporting insurers | 3% to 36% | KFF / CMS |
| Denials attributed to “other, unspecified” | 36% | KFF / CMS |
| Denials attributed to administrative reasons | 25% | KFF / CMS |
| Denials for excluded services | 13% | KFF / CMS |
| Denials for missing prior authorization or referral | 9% | KFF / CMS |
| Denials for medical necessity | 5% | KFF / CMS |
| Share of denied in-network claims appealed | Under 1% | KFF / CMS |
| Internal appeals upheld by insurer | 66% | KFF / CMS |
| Average denial rate, all NAIC-reporting plans, 2024 | 16% | NAIC Market Conduct Annual Statement |
| Medicare Advantage prior authorization denial rate, 2024 | ~8% | KFF analysis of federal data |
| Traditional Medicare prior authorization denial rate, 2024 | ~23% | KFF analysis of federal data |
| Medicaid managed care prior auth denial rate, 2019 | ~13% | HHS Office of Inspector General |
| MA prior auth denials that met Medicare coverage rules | 13% of sampled denials | HHS OIG, OEI-09-18-00260 (2022) |
| MA payment denials that met Medicare coverage and MAO billing rules | 18% of sampled denials | HHS OIG, OEI-09-18-00260 (2022) |
One statistic deserves special attention. You may come across claims that U.S. healthcare denials cost $262 billion annually, with 86% considered avoidable. Although this figure is frequently repeated throughout the industry, it originates from a Change Healthcare analysis that is not publicly available as a verifiable primary source.
For that reason, this guide does not rely on it. Whenever vendors cite this statistic without linking to an accessible primary publication, it should be viewed cautiously.
Read the denial before you work it
Each line on an 835 Electronic Remittance Advice (ERA) includes a Group Code, a CARC, and in many cases a supporting RARC. Understanding the Group Code first is critical because it determines whether the balance can actually be recovered.
- CO (Contractual Obligation): The provider is financially responsible, and the patient generally cannot be billed.
- PR (Patient Responsibility): The balance belongs to the patient and should typically move to patient billing rather than the appeals queue.
- OA (Other Adjustment): Used for miscellaneous payment adjustments.
- PI (Payer Initiated Reduction): Indicates a payer adjustment that is often eligible for review or appeal.
CARC definitions are standardized and maintained by X12, ensuring consistency across the industry. However, payers may apply the same CARC differently depending on their internal policies.
Because of this, the payer’s own provider manual should always take precedence over any generic denial code reference—including this guide.
The 10 denial codes and the appeal move for each
Each denial below explains what the code means, the most common reason it occurs, and the recommended next step. One of the biggest lessons in denial management is recognizing that many denials should be corrected rather than appealed. Proper triage at the beginning often produces the highest recovery rates.
1. CO-16 — Claim lacks information or has submission errors
In most situations, CO-16 does not require an appeal. Instead, it indicates that required information is missing, while the accompanying RARC specifies exactly what needs to be corrected.
Common causes
- Missing modifiers
- Missing or incorrect NPI
- Incomplete patient demographics
- Required claim fields left blank during charge entry
Appeal playbook
Review the accompanying RARC before taking any action. Correct the identified issue and submit the claim as a corrected claim, not as an appeal, because the payer never completed a full adjudication.
If CO-16 repeatedly appears for the same issue, investigate upstream workflows. High volumes usually point to problems with registration or charge-entry templates rather than isolated billing errors.
2. CO-97 — Service is bundled into another paid service
An appeal is appropriate only when the billed services were truly separate and distinct. Success largely depends on using the correct modifier and providing documentation that clearly demonstrates the services should not have been bundled.
Common causes
- National Correct Coding Initiative (NCCI) edit pairs
- Missing Modifier 25 for a separately identifiable Evaluation and Management (E/M) service performed on the same day as a procedure
- Missing Modifier 59 for distinct procedural services
Appeal playbook
First, verify that the NCCI edit applies and determine whether the payer allows a modifier override. If documentation supports a significant, separately identifiable service, submit a corrected claim with the appropriate modifier and include clinical notes demonstrating the separate work performed.
If the payer correctly bundled the services according to policy, accept the adjustment and avoid rebilling the same combination.
3. CO-197 — Precertification or authorization absent
Appeals should focus on retroactive authorization when permitted by the payer or on emergency and urgent-care exceptions when applicable. According to KFF’s analysis of CMS data, missing prior authorization or referrals accounted for 9% of reported in-network denial reasons in 2024.
Common causes
- Prior authorization was never obtained.
- Authorization was approved for a different CPT code.
- Authorization expired before the date of service.
- Authorization was issued under a different rendering provider.
Appeal playbook
Before filing an appeal, confirm whether authorization exists under a different provider, CPT code, or authorization number. Many CO-197 denials result from clerical mismatches rather than an actual lack of authorization.
If the service qualified as an emergency, reference the prudent layperson standard during the appeal. Where payer policies allow retroactive authorization, submit the request within the approved timeframe.
Reducing CO-197 denials begins with strong front-end authorization tracking, making prevention far more effective than recovery.
4. CO-50 — Not deemed a medical necessity by the payer
CO-50 represents a true clinical denial and is often one of the highest-value categories to appeal. Although medical necessity accounted for only 5% of reported denial reasons in 2024, these claims frequently involve significant reimbursement amounts.
Common causes
- Diagnosis codes do not support the billed procedure.
- Clinical documentation fails to satisfy payer coverage requirements.
- Medicare LCD or NCD criteria were not met.
Appeal playbook
Retrieve the payer’s medical policy or the applicable Medicare Local Coverage Determination (LCD) or National Coverage Determination (NCD). Structure the appeal around each specific coverage requirement rather than relying on general clinical explanations.
Include only documentation that directly supports each required criterion, along with a physician’s letter of medical necessity when the clinical rationale is not sufficiently documented within the medical record.
Policy-driven appeals consistently perform better than generic appeal letters.
5. CO-29 — Time limit for filing has expired
This denial should only be appealed when there is documented evidence that the original claim was submitted within the payer’s filing deadline. Without proof such as a clearinghouse acknowledgment or payer acceptance report, recovery is generally unlikely, and the balance typically cannot be transferred to the patient.
Common causes
- Claims remained in work queues too long.
- Previously denied claims were never reworked.
- Coordination of Benefits (COB) delays caused secondary claims to miss filing deadlines.
Appeal playbook
Provide the 277CA acknowledgment or clearinghouse acceptance report showing the original submission date occurred within the payer’s timely filing window.
For Coordination of Benefits situations, reference the primary payer’s remittance date as the starting point for the secondary payer’s filing timeline.
When no supporting documentation exists, write off the balance and treat the denial as an operational issue requiring workflow improvements. CO-29 represents one of the most preventable forms of revenue loss and should trigger immediate process review.
6. CO-18 — Duplicate claim or service
Appeal this denial only when the services were legitimately performed more than once. In most cases, CO-18 accurately identifies duplicate submissions, while successful appeals usually involve repeat services provided on the same date under appropriate circumstances.
Common causes
- The same claim was submitted multiple times.
- Separate same-day services appeared identical to the payer’s duplicate claim detection system.
Appeal playbook
Before taking action, determine whether the earlier claim has already been paid, denied, or is still awaiting adjudication. Pursuing an appeal while the original claim is pending only increases unnecessary workload.
If repeat services were medically necessary and properly documented, resubmit the claim with the appropriate repeat-procedure modifier and include supporting documentation identifying the different treatment times, anatomical sites, or clinical circumstances.
A growing number of CO-18 denials often indicates that staff are resubmitting claims instead of verifying claim status before taking action.
7. CO-45 — Charge exceeds fee schedule or contracted amount
CO-45 is generally not a true denial. Instead, it reflects the contractual adjustment applied after the claim has already been processed. Appeals are appropriate only when there is evidence that the payer reimbursed using an incorrect contracted rate.
Common causes
- Standard contractual write-offs based on the provider agreement.
- Incorrect or outdated fee schedules loaded by the payer.
Appeal playbook
Compare the payer’s allowed amount with the contracted reimbursement rate for the applicable CPT code and geographic region.
If the payment matches the contract, simply post the contractual adjustment.
If the reimbursement differs from the agreed rate, escalate the issue as a payer contract dispute rather than a standard claim appeal. Provide documented comparisons across multiple affected claims when possible.
An isolated underpayment may be a processing error, whereas repeated discrepancies often indicate a payer fee schedule configuration issue that requires provider relations involvement.
8. CO-109 — Claim not covered by this payer or contractor
CO-109 is rarely resolved through an appeal because it typically results from billing the wrong insurance payer rather than a payment determination.
Common causes
- Claims submitted to Traditional Medicare instead of a Medicare Advantage plan.
- Incorrect payer identification selected during claim submission.
- Coverage ended before the date of service.
Appeal playbook
Verify the patient’s insurance eligibility specifically for the date of service, rather than relying on current eligibility information.
Identify the correct insurance carrier and submit the claim promptly, since the timely filing deadline with the appropriate payer continues to run regardless of where the claim was originally sent.
If incorrect insurance information was provided during registration, determine whether patient responsibility applies according to your organization’s financial policies.
9. CO-96 — Non-covered charges
Always review the accompanying RARC before deciding how to proceed. CO-96 may indicate either a genuine benefit exclusion—which generally cannot be appealed—or a coverage determination that may qualify for appeal. According to CMS data analyzed by KFF, excluded services represented 13% of reported in-network denial reasons during 2024.
Common causes
- The service is excluded under the patient’s benefit plan.
- The claim failed to demonstrate that coverage requirements were satisfied.
Appeal playbook
Use the accompanying RARC to determine whether the denial relates to a plan exclusion or a coverage determination.
If the service is truly excluded, responsibility shifts to the patient only when proper advance notification exists, such as a signed Advance Beneficiary Notice (ABN) for Medicare patients.
If coverage criteria were not adequately demonstrated, prepare the appeal using the payer’s specific benefit language and supporting clinical documentation.
Comprehensive benefit verification during patient registration helps reduce many CO-96 denials before services are rendered.
10. PR-27 — Expenses incurred after coverage terminated
PR-27 generally should not be treated as a payer appeal. Since the Group Code is PR, financial responsibility typically belongs to the patient. The primary objective is verifying the patient’s coverage status and determining whether alternative insurance was active.
Common causes
- Insurance coverage terminated before the date of service.
- The patient changed employers or insurance plans.
- Eligibility was verified only once for an ongoing course of treatment.
Appeal playbook
Confirm the coverage termination date directly with the payer, as retroactive eligibility updates occasionally occur.
Investigate whether another insurance policy became effective on the service date. If replacement coverage exists, submit the claim to the appropriate payer.
If no active coverage is identified, transfer the balance to patient responsibility while maintaining complete documentation supporting the eligibility findings.
For recurring treatment plans, establish a process to verify insurance eligibility on a regular basis—such as monthly—instead of relying solely on the initial registration verification.
The appeal deadlines that decide everything
For Original Medicare, providers have 120 days from receiving the initial determination to submit a Level 1 Redetermination request. Medicare presumes receipt occurs five calendar days after the notice date. Missing this deadline can permanently eliminate the opportunity to recover payment, regardless of the strength of the appeal.
Medicare’s fee-for-service appeals process consists of five levels, each with its own filing deadline. Commercial insurers establish their own appeal timeframes through provider contracts, and many of those deadlines are significantly shorter than Medicare’s.
To avoid missed opportunities, practices should record appeal deadlines immediately when a denial is received rather than waiting until the claim reaches the appeals work queue.
| Level | Who decides | Deadline to file | Decision timeframe |
|---|---|---|---|
| 1. Redetermination | Medicare Administrative Contractor | 120 days from receipt of initial determination | 60 days |
| 2. Reconsideration | Qualified Independent Contractor | 180 days from redetermination decision | 60 days |
| 3. ALJ Hearing | Office of Medicare Hearings and Appeals | 60 days from reconsideration decision | Statutory target; actual timelines vary due to backlogs |
| 4. Appeals Council Review | Medicare Appeals Council | 60 days from ALJ decision | Statutory target; actual timelines vary |
| 5. Judicial Review | Federal District Court | 60 days from Appeals Council decision | Court schedule |
Source: CMS Medicare Claims Processing Manual Chapter 29 and CMS Appeals Guidance.
Levels 3 and 5 also require minimum amounts in controversy that are updated annually, so providers should verify the current CMS requirements before filing.
Why so few appeals get filed, and what that costs
Data suggests that healthcare organizations appeal only a small fraction of denied claims. In 2024, less than 1% of denied in-network Marketplace claims were appealed, according to KFF. Of those appeals that were submitted, insurers upheld approximately 66%, meaning roughly one-third resulted in a reversal.
It is important to recognize that these KFF figures reflect consumer appeals, not provider appeals. Comparable nationwide reporting for provider appeals is not available. Even so, the underlying challenge is familiar across medical billing operations. Appeals require staff time, reimbursement is never guaranteed, and lower-dollar denials are often written off instead of being pursued.
Although this approach may seem reasonable when evaluating individual claims, it can create substantial financial losses over time. Every denial that is never worked becomes a complete revenue loss. Even when an appeal is unsuccessful, the only additional cost is the staff effort involved. For many organizations, developing standardized appeal templates for common denial codes makes appealing far more cost-effective than abandoning claims.
Additional evidence comes from the HHS Office of Inspector General’s review of Medicare Advantage organizations. After examining a representative sample of denials from 15 of the nation’s largest Medicare Advantage plans, the OIG found that 18% of denied payment requests actually complied with both Medicare coverage requirements and the plan’s own billing policies.
Most of these inappropriate denials resulted from manual review mistakes or automated system processing errors rather than genuine coverage disputes.
This finding is significant. Nearly one out of every five denied payment requests reviewed should have been paid correctly during the initial claim adjudication. In many situations, success does not depend on convincing the payer to change its decision—it simply requires identifying and documenting the payer’s processing error before the claim is written off.
Fixing the source instead of the symptom
Recovering denied claims is only one part of an effective denial management strategy. Long-term improvement comes from preventing the same denials from occurring again.
Begin by tracking every denial according to:
- Denial code
- Insurance payer
- Rendering provider
- CPT code
- Root cause
After several months of tracking, recurring trends typically become apparent. Many denials originate from a limited number of operational issues, such as incomplete registration fields, payer-specific authorization requirements that scheduling teams overlook, or coding patterns where required modifiers are consistently missed.
Once these patterns are identified, responsibility should be assigned to the department responsible for creating the issue rather than leaving everything with the billing team.
For example:
- CO-16 should be addressed through registration or charge-entry improvements.
- CO-197 requires stronger scheduling and prior authorization workflows.
- CO-29 highlights deficiencies in claim follow-up and work queue management.
- CO-50 points to opportunities for improving clinical documentation.
When every denial is routed back to billing alone, the underlying problems remain unresolved because billing functions downstream from the departments where many denials originate.
How Synergy HCLS handles denials
At Synergy HCLS, denial management is handled as a continuous improvement process rather than simply processing claims through an appeals queue. Every denial is analyzed to determine its root cause, appealed whenever supporting documentation justifies recovery, and shared with the appropriate department to help prevent similar denials in the future.
Our Revenue Cycle Management (RCM) team develops payer-specific appeal templates so that each appeal reflects the individual payer’s policies instead of relying on generic language. This allows clinical appeals, including CO-50 medical necessity denials, to address the exact coverage requirements established by each insurance carrier.
Our Medical Coding team continuously reviews coding patterns, diagnosis selection, and modifier usage to reduce denials related to bundling edits and medical necessity.
Meanwhile, our Medical Billing specialists closely monitor timely filing deadlines and claim follow-up processes, helping practices minimize preventable denials such as CO-29 before they occur.
Synergy HCLS partners with independent healthcare practices across more than 38 medical specialties, delivering comprehensive Revenue Cycle Management services designed to improve reimbursement, reduce denials, and strengthen long-term financial performance.
Denial management checklist
☐ Every denial is assigned a documented root cause rather than only a CARC.
☐ Appeal deadlines are recorded immediately when the denial is received.
☐ Claims are categorized as correct, appeal, or write-off before additional work begins.
☐ Payer-specific appeal templates exist for the five most common denial codes.
☐ Appeals reference the payer’s own medical policies instead of relying solely on general clinical reasoning.
☐ Documentation proving timely filing is available for every submitted claim.
☐ Eligibility is reverified for recurring treatment series instead of only during initial registration.
☐ Denial trends are shared with scheduling, registration, coding, and clinical departments—not only the billing team.
☐ Low-dollar denials follow predefined recovery thresholds rather than informal write-off decisions.
☐ Denial rates are monitored by payer because national averages do not reflect the significant variation between individual insurers.
About Synergy Healthcare
Synergy Healthcare & Life Sciences (Synergy HCLS) is a USA-based leading medical billing and coding outsourcing company, specializing in Revenue Cycle Management (RCM) solutions.
With over 25 years of combined experience, Synergy HCLS helps physicians, clinics, and healthcare organizations improve cash flow, reduce denials, and ensure HIPAA-compliant documentation.
Their services include medical billing, medical coding, physician credentialing, accounts receivable management, transcription, and record summarization, making them a trusted partner for healthcare providers across multiple specialties.
Frequently Asked Questions
Denial management is the process of identifying why an insurance payer denied a claim, correcting or appealing the denial when appropriate, and addressing the underlying operational issue to prevent the same denial from recurring. Effective denial management combines root-cause analysis, reimbursement recovery, and process improvement.