ACA insurers still reject 1 in 5 claims, leaving millions with unpaid bills

SAN FRANCISCO, Calif. — November 2025 — Affordable Care Act insurers approved more claims in 2024, though the improvement remains modest. Nearly one in five in-network claims (19.1%) were denied, leaving millions of Americans with unpaid medical bills despite having coverage, according to a new analysis by MoneyGeek, which reviewed comprehensive claims data from all ACA Marketplace insurers reporting to CMS for plan year 2024.

Covering approximately 46 million in-network claims across HealthCare.gov states, the analysis shows that denials vary widely by state and insurer. Rejection rates top 25% in some markets, while others approve more than 95% of claims. These findings arrive during the 2026 open enrollment, when understanding which insurers deny the most claims can help Americans make smarter coverage choices.

"Three in four denials (77%) stem from paperwork or plan design, not medical judgment," said Mark Fitzpatrick, licensed insurance expert at MoneyGeek. "Denial rates vary by 500% across states and 40% across insurers, making plan selection during open enrollment a critical financial decision."

Key findings

• Denial rates fell from 22.5% in 2023 to 19.1% in 2024, the first meaningful improvement in four years. The 2024 rate represents a partial recovery from the 2022 spike to 22.5% but remains above the 2021 baseline of 16.7%.
• Approximately 8 million of 46 million in-network claims were denied across HealthCare.gov states in 2024.
• Three in four denials (77%) stem from paperwork or plan design, not medical judgment.
• Hawaii (26.9%) and Alaska (25.5%) had the highest denial rates; South Dakota (5.4%) the lowest.
• Oscar Health (25.3%) and Molina Healthcare (22%) denied the most claims among major national insurers. UnitedHealthcare, the nation's largest insurer, dropped 15 points from 34.2% to 19.1% across 6.4 million claims.
• Consumers rarely appeal: fewer than 0.2% of denied claims were appealed internally, and 56% of those appeals were upheld.

Why denial rates matter now

Open enrollment for 2026 is underway as MoneyGeek's separate analysis found that premiums rose 20% nationally this year. A low premium means little if your insurer denies one in four claims. Coverage access remains a challenge, with 27 million Americans still uninsured, as enhanced ACA subsidies are set to expire in 2026.

Federal transparency rules have improved accountability since 2015, yet 2024's improvement marks only a partial recovery from persistently high denial rates. Nearly a decade of transparency requirements hasn't driven meaningful change in insurer behavior across all markets.

Denied claims can delay care or result in surprise medical bills, even for in-network services that patients reasonably believed were covered. Some denied claims get paid after resubmission without formal appeals, meaning persistence pays off even without the full appeals process.

Methodology

MoneyGeek analyzed the Transparency in Coverage (TiC) 2026 Public Use File from CMS, covering Plan Year 2024 claims reported in 2025. The dataset includes Qualified Health Plan (QHP) filings from individual ACA Marketplace insurers, excluding Small Business Health Options (SHOP) and Stand-Alone Dental Plans (SADPs).

Metrics reflect in-network, post-service claims only. MoneyGeek included all insurers reporting at least 1,000 claims in plan year 2024, regardless of whether they continued offering plans in 2025. This captures the experience of patients who filed claims during 2024, including those covered by insurers that later exited the Marketplace.

MoneyGeek rounded values to whole percentages for readability and excluded plans with suppressed or incomplete reporting.

Complete interactive data and methodology: ACA Marketplace Premiums Surge 20% Nationwide in 2026