Which US Health Insurer Denies the Most Claims? Data-Driven Analysis

Insurance Denial Rates by Insurer (2026)" class="auto-link">denial rates are one of the most important — and least transparent — data points in US healthcare. Patients and employers selecting health plans have historically had little data to compare how often different insurers say no. But public data from CMS, the NAIC, and state insurance departments is more available than most people realize.

Here is what the data actually shows.

The Data Sources Available

CMS ACA Marketplace Data

For ACA marketplace plans (individual and small group), CMS collects and publishes denial rates annually through its transparency in coverage requirements. Insurers must report:

• Number of claims received.
• Number of claims denied.
• Denial rates by reason (not covered benefit, not medically necessary, Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization missing, etc.).

This data covers ACA marketplace plans only — not employer plans (which cover most Americans) and not Medicare or Medicaid directly.

Key finding from CMS data (2022 reporting period): Across ACA marketplace plans, insurers denied approximately 17% of in-network claims on average. But individual insurer denial rates ranged from under 2% to over 49%.

Top deniers in recent CMS data cycles have included:

• UnitedHealthcare/Golden Rule: Denial rates above 30% in some markets.
• Cigna Healthcare: Denial rates significantly above industry average.
• Oscar Health: Early reports showed elevated denial rates but more recent data has improved.
• Ambetter (Centene): Variable by state, with some markets showing high denial rates.

Lower denial rates have historically appeared at:

• Kaiser Permanente: Consistently among the lowest marketplace denial rates due to its integrated care model.
• HCSC/BCBS of Illinois: Competitive denial rates in its markets.

Medicare Advantage Data

CMS publishes Medicare Advantage prior authorization and appeals data. The 2022 OIG report examined MA plan denials comprehensively. Key data points:

• MA plans with the most scrutiny for denials include UnitedHealthcare, Humana, and several regional plans.
• External appeal (QIC) overturn rates — the share of MA denials reversed by independent reviewers — provide the clearest signal of improper denials. Plans with higher overturn rates are denying services they should cover.

NAIC Complaint Ratios

The NAIC Complaint Ratio database compares the number of justified complaints per 10,000 insured for each company. Complaint ratios above 1.0 indicate above-average complaints relative to market share.

Recent NAIC data has shown elevated complaint ratios for:

• Cigna subsidiaries (particularly for claim denials).
• Centene/WellCare plans in several states.
• Some UnitedHealthcare subsidiaries.

Medical Loss Ratio Data

The MLR requirement under the ACA requires insurers to spend at least 80% (individual market) or 85% (group market) of premium revenue on claims and quality improvement. MLR data is publicly available through CMS.

While a low MLR signals an insurer is keeping more money as profit/overhead, it does not directly measure denial rates. However, insurers with persistently low MLRs — near the minimum threshold — are likely managing claims more aggressively.

What the Data Shows Overall

Several consistent patterns emerge from available public data:

1. Denial rates vary enormously — from under 5% to nearly 50% across insurers. Being insured does not mean you have uniform protection; your insurer matters.

2. Prior authorization is a major denial driver: Plans with heavy PA requirements show higher overall denial rates, particularly for specialty care, advanced imaging, and specialty drugs.

3. Employer plan denials are less transparent: The ACA marketplace data and Medicare data provide the best public information, but the majority of privately insured Americans are in employer-sponsored plans governed by ERISA — where denial rate data is not publicly reported.

4. External appeal overturn rates signal inappropriate denials: When 40–50% of appealed decisions are reversed by independent reviewers, those denials should not have been issued in the first place.

5. Integrated systems (Kaiser) deny less: Kaiser Permanente's low marketplace denial rates reflect its model — when the insurer and provider are integrated, the denial decision and the clinical decision are the same. This can mean more clinical judgment and less administrative friction.

The Limits of Public Data

Public denial rate data has real limitations:

• It covers marketplace plans, not employer plans.
• Denial definitions vary — some insurers count prior auth denials; others do not.
• High denial rates for some insurers may reflect higher proportions of complex claims.
• Data is reported with a one-to-two-year lag.

The most complete picture requires combining CMS denial data, NAIC complaint ratios, MLR data, and state-specific reports.

What to Do With This Information

• When choosing a plan: Review available denial rate data for your market. Medicare.gov star ratings incorporate member experience data including appeals. State insurance department annual reports sometimes include plan-specific complaint data.
• When you've been denied: Knowing your insurer has an elevated denial rate context is useful in an appeal — but the appeal itself must address the specific clinical criteria.
• When advocating for systemic change: The data supports broader transparency requirements and regulatory enforcement.

Fight Back With ClaimBack

Regardless of which insurer denied your claim, the appeal process follows recognizable rules. ClaimBack helps you build the strongest possible appeal — whatever the insurer.

Start your appeal at ClaimBack

Related Reading

• How to Write an Insurance Appeal Letter
• Common Reasons Insurance Claims Are Denied
• Internal vs. External Insurance Appeals