ACA Insurers Still Reject 1 in 5 Claims, Leaving Millions With Unpaid Bills

Affordable Care Act (ACA) insurers approved a higher share of claims in 2024 after years of stagnation, but the improvement remains modest. Nearly one in five in-network claims (19.1%) were still denied, leaving millions of Americans with unpaid medical bills despite having coverage.

MoneyGeek analyzed comprehensive claims data from all ACA Marketplace insurers reporting to CMS for plan year 2024. Denials vary widely, with rejection rates topping 25% in some markets while others approve more than 95% of claims.

Open enrollment for 2026 is underway. Understanding which insurers deny the most claims helps consumers choose better coverage.

Denial rates hovered between 20% and 23% since 2021, making 2024's decline the first sustained improvement. The national average dropped 3.4 percentage points year-over-year, a 15% relative decline.

Wide variation persists, with states that have few participating insurers continuing to post high rejection rates. Alabama led improvements with a 15-point drop, while Montana and North Dakota each fell more than 10 points. Five states worsened, with Alaska climbing 5 points to reach the second-highest denial rate nationally.

Major Insurers Show Mixed Performance

Blue Cross Blue Shield of Montana posted the biggest improvement, dropping 27 percentage points from 39.4% to 12.5%. UnitedHealthcare's 15-point decline carries more weight given its volume of 6.4 million claims, a shift affecting millions of patients. Blue Cross Blue Shield of Alabama improved 16 points, falling from 34.8% to 19%.

Oscar Health and Molina Healthcare moved in the opposite direction. Oscar Health climbed 7 points to 25.3%, the highest denial rate among major national insurers. Molina Healthcare rose 3 points to push above 20%. The 10 largest carriers still dropped their average denial rate from 23.2% to 19.4%, a 3.8-point improvement.

Denial rates ranged from 5% to 27% in 2024, a fivefold difference. Hawaii and Alaska denied the most claims, while South Dakota and North Dakota denied the fewest. Market size doesn't drive performance: Florida and Texas exceeded the national average despite having 11 and 14 competing insurers, respectively.

Insurer performance varies as sharply as state rates, with denial rates ranging from 18% to 25% among the 10 largest carriers. Oscar Health denied one in four claims (25%), the highest rate among major national insurers. UnitedHealthcare processed the most claims at 6.4 million, denying 20% despite its 15-point improvement from 2023.

*Blue Cross and Blue Shield parent companies from different states operate independently and are separated in this analysis.

Administrative issues and coverage disputes accounted for nearly two-thirds of rejections in 2024, with medical necessity playing a minor role. Three in four denials (77%) stem from paperwork or plan design, not medical judgment.

Insurers argue administrative denials help prevent duplicate billing and fraud. Consumer advocates counter that the burden falls unfairly on patients who submitted claims correctly but face rejection due to insurer processing errors.

Of 8.8 million denied claims in 2024, very few consumers challenged denials through formal appeals:

• 0.2% of denied claims were appealed internally (approximately 17 appeals per 10,000 denied claims).
• 56% of those internal appeals were upheld by insurers.
• Fewer than one per 10 million denied claims reached external appeal with an independent reviewer.

Only 40% of Marketplace enrollees know they have a right to an independent external review, according to KFF's 2023 survey. Enrollees with ACA plans (34%) were less likely to know about external appeal rights compared to those with Medicare (58%) and Medicaid (45%).

Some denied claims get paid after resubmission without formal appeals. Persistence pays off even without the full appeals process.

Denied claims can delay care or create surprise medical bills, even for in-network services that patients reasonably believed were covered. When insurers reject claims, patients may owe thousands in unexpected medical expenses.

Denial rates vary by 500% across states and 40% across insurers, making plan selection during open enrollment a critical financial decision. Understanding which insurers and states deny the most claims helps consumers choose plans that will actually pay when they need care.

Premiums rose 20% nationally for 2026, but rate increases vary widely by state and insurer. When evaluating plans, weigh both upfront costs and how often insurers pay claims. 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 face expiration 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.

Some denied claims get paid after resubmission without formal appeals. Persistence pays off even without the full appeals process.

Compare denial rates before choosing a Marketplace plan during open enrollment to avoid insurers with high rejection rates.

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.

Data Selection

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.

How We Calculated Rates

For each insurer and state, we calculated:

• Weighted denial rates = claims denied ÷ claims received (weighted by claim volume)
• Median issuer rate per state = middle value when insurers ranked by denial rate
• National insurer averages = combined rates for insurers reporting across multiple states

MoneyGeek rounded values to whole percentages for readability and excluded plans with suppressed or incomplete reporting.
CMS reports claim counts in raw numbers. For readability, MoneyGeek displays values in thousands in tables (e.g., 5,200 in the table represents 5.2 million actual claims). Totals reflect in-network, post-service medical claims only, excluding pharmacy and stand-alone dental claims.

Limitations

This analysis covers only HealthCare.gov states. States operating their own marketplaces (California, New York, Massachusetts, Washington, Colorado, Connecticut, Maryland, Minnesota, Nevada, New Jersey, Pennsylvania, Rhode Island and Vermont) aren't included.

Insurers participating in HealthCare.gov states in 2024 but not in 2026 didn't provide claims denial information. Data are self-reported and not independently audited.

Claims initially denied but later resubmitted and approved don't count as denied. Parent company names were obtained by merging the 2025 QHP landscape file with Medical Loss Ratio submission data using HIOS plan identification numbers.