Aetna vs. UnitedHealthcare: Denial Rates by Insurer (2026)" class="auto-link">Denial Rates, Complaints, and Appeal Outcomes Compared

Aetna and UnitedHealthcare are two of the five largest health insurers in the United States. Together they cover tens of millions of Americans through employer-sponsored plans, individual and family plans, Medicare Advantage, and Medicaid managed care. When choosing between them — or when deciding whether to appeal a denial — the differences in their denial rates, complaint histories, and appeal outcomes matter.

Scale and Market Position

UnitedHealthcare is the largest health insurer in the United States by revenue and enrollment, with over 50 million covered lives as of recent reports. It operates through its parent company UnitedHealth Group, which also owns Optum (a major pharmacy benefit manager and healthcare services company). This vertical integration means UnitedHealthcare controls large parts of the care delivery pipeline.

Aetna is the third-largest US health insurer, now owned by CVS Health following a 2018 merger. The CVS integration similarly positions Aetna within a vertically integrated health services company that includes pharmacy, MinuteClinics, and specialty care.

Both companies operate national PPO and HMO networks, Medicare Advantage plans, Medicaid managed care contracts, and employer group plans across all 50 states.

Claim Denial Rates

CMS data published annually shows Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization denial rates and claim denial rates for Medicare Advantage plans, which provide the most transparent insurer-by-insurer comparison available for any major coverage segment.

In recent CMS data cycles:

• Both Aetna and UnitedHealthcare Medicare Advantage plans have shown above-average prior authorization denial rates compared to the Medicare Advantage industry average.
• UnitedHealthcare has faced particular regulatory scrutiny: a 2023 Senate Finance Committee investigation found UnitedHealthcare's subsidiary NaviMed denied post-acute care claims at rates far exceeding industry norms.
• Aetna received CMS sanctions in 2023 related to Medicare Advantage coverage determinations and was required to implement corrective actions.

For commercial plans, CMS publishes MLR (Medical Loss Ratio) data and state-level complaint data that provides additional context. CMS does not directly publish commercial plan denial rates.

NAIC Complaint Ratios

The National Association of Insurance Commissioners (NAIC) publishes complaint ratios comparing the number of complaints filed against each insurer to their market share. A ratio above 1.0 means an insurer receives more complaints than its market share would predict.

Historically:

• UnitedHealthcare operating entities have received higher complaint ratios in several states, particularly for claim denial and claim handling.
• Aetna complaint ratios have been more variable by state and year.

The NAIC complaint database is publicly searchable and allows consumers to check their specific state's data.

Appeal Win Rates

For ACA marketplace plans, CMS collects and publishes data on internal and external appeal outcomes. The external appeal win rate — how often a state or IROs) Explained" class="auto-link">independent review organization overturns an insurer's denial — is one of the clearest measures of whether a denial was justified.

Industry-wide, approximately 40–60% of external appeals of health insurance denials succeed. Insurers with higher denial rates that are overturned at External Independent Review: Complete Guide" class="auto-link">external review are denying claims they should have approved.

Both Aetna and UnitedHealthcare have experienced external appeal overturn rates consistent with industry averages, meaning a meaningful share of their denials can be successfully challenged.

Prior Authorization Burden

Prior authorization (PA) requirements — requiring insurer approval before receiving care — affect patients of both companies heavily.

UnitedHealthcare has faced criticism from physician groups and hospital systems for its PA volume. The American Medical Association's annual PA surveys have consistently cited UnitedHealthcare as among the insurers with the highest PA burden on physicians.

Aetna has also faced criticism but has taken some public steps to reduce PA requirements for certain categories of services, including announcing reductions in PA for some surgical procedures.

Plan Quality: NCQA and CMS Star Ratings

NCQA (National Committee for Quality Assurance) rates health plans on quality measures including preventive care, chronic disease management, and member experience. Both Aetna and UnitedHealthcare operate plans that span the rating spectrum — from 2 to 5 stars — depending on the specific market and plan type.

CMS Star Ratings for Medicare Advantage plans are publicly available. In recent rating cycles, some UnitedHealthcare MA plans have received lower ratings due to member experience metrics, while some Aetna plans have maintained strong clinical quality scores.

Which Is Better for Appeals?

Both insurers maintain internal appeal processes with 30 and 60-day review timelines (depending on urgency). Both are subject to state external appeal rights for individual and small group plans, and to ERISA external claims review for large employer plans.

From a practical standpoint:

• Document everything and appeal in writing.
• Request the specific clinical criteria used for denial.
• Both companies use InterQual and MCG (formerly Milliman) clinical guidelines, which can be obtained and challenged.

Fight Back With ClaimBack

Whether you have Aetna or UnitedHealthcare, the appeal process follows similar rules — and ClaimBack can help you navigate it effectively.

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