Which Insurance Company Denies the Most Claims? Denial Rates by Insurer 2026

How Insurance Denial Rates Are Measured

Not all denial statistics measure the same thing. The most transparent dataset comes from the ACA marketplace: insurers selling plans on HealthCare.gov are required under the Affordable Care Act to report claims denial data in their Transparency in Coverage filings with CMS.

This article draws primarily from Plan Year 2024 data (reported in 2025) covering approximately 46 million in-network claims across HealthCare.gov states. The analysis excludes state-operated exchanges (California, New York, Massachusetts, and others), employer-sponsored plans, and Medicaid managed care — which means the figures below reflect commercial marketplace performance only.

Medicare Advantage prior authorization denial rates follow a separate reporting structure through CMS and are noted separately where relevant.

Denial Rates by Insurance Company (2024 ACA Marketplace Data)

The table below ranks major national insurers by their in-network ACA marketplace claim denial rate for Plan Year 2024, based on CMS Transparency in Coverage reporting analyzed by MoneyGeek (published January 2026).

Source: CMS Transparency in Coverage Public Use File, Plan Year 2024, reported in 2025. Analyzed by MoneyGeek. Rates reflect in-network claims for HealthCare.gov states.

Key takeaway: There is a nearly 20 percentage point gap between the highest-denying national insurer (Oscar at 25.3%) and Kaiser Permanente (approximately 6%). The range across all 175 reporting insurers was 2% to 49%, meaning plan selection matters significantly for practices managing denial volume.

Why Oscar and Molina Deny More Claims

Oscar Health and Molina Healthcare operate primarily in the ACA marketplace and Medicaid, respectively. Marketplace-focused plans tend to have higher administrative denial rates because:

• They serve higher-risk enrollees who use more services and trigger more coverage scrutiny
• They rely heavily on prior authorization protocols to control costs
• Their claims adjudication systems generate more administrative and eligibility rejections

For Molina, Medicaid managed care enrollment also means stricter medical necessity criteria enforced at lower reimbursement rates — which correlates with higher denial rates in ACA marketplace filings.

Neither insurer publishes CPB-style clinical policy bulletins to the same depth as Aetna or UHC, which can make appeals harder to construct without insurer-specific guidance.

UnitedHealthcare: A 13-Point Drop Worth Watching

UHC's decline from 33% (2023) to 20% (2024) is the most notable year-over-year shift among major insurers. The company processed 6.4 million ACA marketplace claims in 2024.

Several factors likely contributed:

• Increased regulatory scrutiny following publicized denial controversies in 2024
• Policy changes to prior authorization requirements for certain procedure categories
• Improved administrative processing to reduce technical denials

However, 20% still means UHC denies one in five in-network marketplace claims. For practices with significant UHC volume, that is a material revenue exposure. See the UHC appeal letter template 2026 for the correct format and submission requirements.

Aetna Denial Rates

Aetna reported approximately 22% in-network ACA claim denial rates in 2023 data (per KFF analysis), placing it above the national average. For Medicare Advantage prior authorization specifically, Aetna's denial rate was 14.4% — among the higher MA prior auth rates nationally.

Aetna's denial patterns, state-level variation, and appeal overturn data are covered in detail in Aetna Denial Rate Statistics 2026. For building a specific appeal, the Aetna appeal guide 2026 covers the step-by-step process.

BCBS Denial Rates: Affiliate Variation Is Extreme

The 18% aggregate BCBS figure in the 2024 data obscures enormous variation across the 36 independent BCBS licensees. Analysis of 2023 state-level data found:

• Alabama BCBS: approximately 34% average denial rate — one of the highest state averages nationally
• Wisconsin BCBS: approximately 16%
• Other affiliates range from single digits to above 30%

If your practice works with a specific BCBS affiliate, the national aggregate is nearly meaningless. What matters is the performance of your state plan.

Kaiser Permanente: Why the Integrated Model Produces Fewer Denials

Kaiser Permanente consistently denies roughly 6% of in-network claims — the lowest rate among major national insurers offering ACA plans in seven or more states. The integrated care model, where Kaiser operates both the insurance plan and the delivery system, reduces several friction points that generate denials elsewhere:

• Authorization requirements are largely internal, eliminating third-party PA delays
• Claims are adjudicated within the same organization that delivered care
• Provider documentation practices align with plan criteria by design

The tradeoff is network access: Kaiser's closed network means most independent practices do not contract with Kaiser, limiting the relevance of their low denial rate for most billing teams.

State-Level Denial Rate Variation (2024)

Even within the same insurer, denial rates vary substantially by state. Plan Year 2024 state-level data shows:

Source: CMS Transparency in Coverage Public Use File, Plan Year 2024, analyzed by MoneyGeek.

Florida's range — 8% to 49% across plans — illustrates how much insurer choice within a state matters. Two patients in the same city on different ACA plans can face dramatically different denial rates for identical services.

What Causes Most Denials?

According to KFF analysis of 2023 ACA marketplace data, approximately 77% of denials stem from paperwork and plan design issues rather than clinical judgment:

• 34% — "Other" administrative reasons
• 18% — Administrative processing issues
• 16% — Excluded or non-covered services
• 9% — Lack of prior authorization or referral
• 6% — Medical necessity determination

This means the majority of denials are potentially reversible through an appeal that addresses the specific administrative or coverage issue — not through complex clinical arguments.

Appeal Success Rates: The Opportunity Most Practices Miss

KFF analysis of 2023 ACA marketplace data found that fewer than 1% of denied claims were ever appealed — despite a 44% internal appeal overturn rate. That gap represents a large amount of recoverable revenue sitting uncollected.

For prior authorization denials specifically, the AMA's 2024 Prior Authorization Physician Survey (n=1,004 physicians) found that over 80% of prior authorization appeals ultimately succeed when pursued. The bottleneck is not success probability — it is the time and friction required to build and submit appeals.

Which Insurer Is Hardest to Appeal?

There is no publicly available insurer-by-insurer breakdown of appeal overturn rates for ACA marketplace plans. Each major insurer publishes its internal appeal outcome data inconsistently, and CMS does not require appeal-level reporting at the insurer tier.

What practices report anecdotally:

• Aetna appeals tend to require specific CPB-aligned documentation and respond well to structured medical necessity arguments referencing their clinical policy bulletins
• UHC appeals involve navigating UHC's Provider Appeal system and often benefit from citing UpToDate or peer-reviewed literature
• Cigna expedited appeals through PromptPA and EviCore require understanding which pathway applies — see the Cigna PromptPA Guide 2026
• BCBS affiliate processes vary significantly by state; the national template does not apply uniformly
• Oscar and Molina have less publicly documented appeal guidance, requiring more direct phone engagement to understand the specific denial basis

Regardless of insurer, missing the appeal deadline eliminates the option entirely. Insurance appeal deadlines by company covers the specific filing windows for each major payer.

How Muni Appeals Addresses Denial Volume Systematically

For practices dealing with consistent denial rates across one or more of the insurers above, the core challenge is throughput: building insurer-specific, documentation-matched appeals fast enough to capture recoverable claims before deadlines pass.

Muni Appeals automates the appeal-building process with insurer-specific workflows:

• Insurer-specific appeal logic for Aetna, UHC, BCBS, Cigna, Humana, and Oscar
• Medical necessity documentation structured against each insurer's clinical criteria
• Deadline tracking to prevent missed filing windows
• Consistent formatting that matches each payer's internal requirements

Start 3 Free Appeals

Frequently Asked Questions

Which insurance company denies the most claims?

Oscar Health denied 25.3% of ACA marketplace claims in Plan Year 2024, the highest rate among national insurers offering plans across seven or more states. Molina Healthcare (22%) and Ambetter/Celtic (21%) also denied claims at above-average rates. Kaiser Permanente had the lowest denial rate at approximately 6%.

What is the average health insurance denial rate?

The national average for in-network ACA marketplace claims was 19.1% in Plan Year 2024 — down from 22.5% in 2023. Out-of-network claims are denied at significantly higher rates (approximately 37%). Employer-sponsored plans generally have lower denial rates, though those are reported less transparently.

Did UnitedHealthcare's denial rate go down?

Yes. UHC's ACA marketplace denial rate dropped from approximately 33% in 2023 to 20% in 2024 — a 13 percentage point decline. This was the largest year-over-year improvement among major national insurers. UHC processed approximately 6.4 million in-network claims during the 2024 plan year.

What percentage of insurance appeals are successful?

According to KFF analysis of 2023 ACA marketplace data, 44% of internal appeals successfully overturned the denial. For prior authorization denials specifically, AMA research found over 80% of properly documented appeals succeed. The challenge is that fewer than 1% of denied claims are ever appealed.

Do BCBS plans deny more claims than average?

The aggregate BCBS denial rate was approximately 18% in 2024 — slightly below the national average of 19.1%. However, BCBS operates as 36 independent affiliates, and denial rates by state affiliate range from below 10% to above 30%. The national average does not predict your local plan's behavior.

Why does Kaiser Permanente have such a low denial rate?

Kaiser's integrated model — where the same organization provides insurance coverage and delivers care — eliminates the friction between payer and provider that generates most administrative denials. Claims are adjudicated within the system that treated the patient. Most independent practices do not contract with Kaiser, limiting the practical relevance of this comparison.

Does the insurer's denial rate affect my appeal strategy?

Not directly — the appeal strategy should be based on the specific denial reason code and insurer policy, regardless of that insurer's overall denial rate. High-denial insurers like Oscar may have more administrative denials (easier to fix) versus medical necessity denials (harder). Understanding the denial reason is more actionable than knowing the overall rate.

Are these denial rates the same for employer-sponsored plans?

No. The data in this article covers ACA marketplace plans sold through HealthCare.gov. Employer-sponsored plans are subject to different reporting requirements (ERISA for self-funded plans), and their denial rates are generally not reported with the same transparency. Most large employer plans are self-funded, meaning the employer — not the insurer — bears the risk and sets coverage criteria.

What is Cigna's ACA marketplace denial rate?

Cigna Health & Life denied approximately 19% of in-network ACA marketplace claims in Plan Year 2024 — right at the national average. Cigna routes many specialty and high-cost service prior authorizations through EviCore, a third-party management company, which adds a separate layer of review. Understanding whether a denial came from Cigna directly or from EviCore determines the correct appeal pathway.

How do I appeal a denied insurance claim?

Start by reviewing the denial letter for the specific reason code and the appeal deadline. Most ACA marketplace plans allow 180 days for an internal appeal. Gather the relevant medical records, clinical notes, and any applicable coverage criteria from the insurer's clinical policy bulletins. Submit a written appeal addressing the exact denial reason. If the internal appeal is denied, you have the right to request external review through an independent organization. See the insurance appeal deadlines guide for insurer-specific filing windows.

Does my state affect how often insurance claims are denied?

Yes — significantly. State-level denial rates ranged from 5.4% (South Dakota) to 26.9% (Hawaii) in Plan Year 2024. Florida showed the widest within-state range (8% to 49% across different plans). State insurance regulators also influence how aggressively insurers apply prior authorization requirements, and some states have enacted stronger external review protections than federal minimums require.

Which insurance company is easiest to appeal?

There is no publicly ranked insurer-by-insurer appeal ease metric. However, insurers with detailed, publicly available clinical policy bulletins — Aetna and UHC in particular — give practices a clearer framework for constructing medical necessity arguments. Appeals against Oscar and Molina often require more direct contact with the plan to understand what specific documentation is needed, since neither publishes CPBs with the same consistency as the larger carriers.

Ready to Reduce Denial Impact?

The denial rate data shows that your payer mix significantly shapes your administrative burden. High-denial insurers like Oscar, Molina, and UHC at 20%+ require consistent, structured appeals to recover the revenue that is routinely withheld.

Get Started with Muni Appeals:

• Insurer-specific appeal workflows for every major payer
• Medical necessity arguments built against each insurer's clinical policy criteria
• Deadline tracking so no appeal window closes without action
• Consistent documentation quality across your billing team

Start 3 Free Appeals

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This guide reflects Plan Year 2024 ACA marketplace denial data as reported by CMS Transparency in Coverage filings and analyzed by KFF and MoneyGeek. Data covers HealthCare.gov states only and does not include state-operated marketplaces, employer-sponsored plans, or Medicaid fee-for-service. Insurer-specific denial rates vary by state, plan type, and year. Verify current plan-specific data before making coverage or contracting decisions.