Overturn rates by insurer

The takeaway is uncomfortable but useful: appeals work, and most people simply never file one. The table below shows how the six largest US health insurers compare on denial volume and outcomes.

Verified 2026-06-16. Overturn rate reflects the ~44% federal-HHS aggregate reported by CMS CCIIO where a parent-level figure is not published. Kaiser and Humana are footnoted because they do not report ACA Marketplace data on the same basis (Kaiser sells on state exchanges; Humana exited the Marketplace in 2018).

Denial rate is the share of in-network claims the insurer denied in 2023. It includes both minor administrative denials and full clinical denials. A 22% denial rate does not mean 22% of members were harmed — it means one in five submitted claim lines came back with a "denied" code.

Overturn rate on appeal reports what happens once a patient formally challenges the denial. At the federal-HHS aggregate level, insurers reverse themselves roughly 44% of the time on internal appeal. In California — where the state Department of Managed Health Care publishes IMR outcomes — the external overturn rate is closer to 68%.

Most denials are generated by automated logic (medical policy engines, prior-authorization rulesets, matching against MCG or InterQual). Human clinical review only happens on appeal. That structural gap is why appeals overturn so many denials: the case gets its first real medical look after the patient pushes back.

• Under 29 CFR 2560.503-1, ERISA plans must give members at least 180 days to appeal.
• Under 45 CFR 147.136, Marketplace plans must offer external review within at least 4 months of the final internal denial.
• External review overturn rates run 44%–80% depending on the state.

For step-by-step guidance, see the appeal pillar and the external review outcomes by state.

Denial rates and claim counts are drawn from KFF's analysis of the CMS Transparency in Coverage Public Use Files (PUF) for plan year 2023 (published January 27, 2025; updated March 24, 2026). Overturn rates use the CMS CCIIO federal-HHS aggregate (2022) where a parent-level figure is not disclosed. Kaiser figures are cross-referenced against Covered California's public denial-rate summary. Humana is included for completeness only; the company exited the Individual Marketplace in 2018 and no comparable Marketplace figure exists.

Numbers are re-verified quarterly. If KFF or CMS publishes a newer parent-level figure, this page is updated and the "verified" date at the top of the table changes.