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. The improvement is 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. Rejection rates still top 25% in some markets, while others approve more than 95% of claims.

Open enrollment for 2026 is now underway. Understanding which insurers deny the most claims can help consumers make smarter coverage choices.

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

Wide variation persists. Some states, particularly those with few participating insurers, continue to post high rejection rates. But many states saw meaningful improvement. Alabama led 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 become 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 matters more given its massive volume of 6.4 million claims, representing a market-level shift affecting millions of patients. Blue Cross Blue Shield of Alabama improved 16 points, falling from 34.8% to 19.0%.

Not all insurers improved. 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%. Despite these declines, the 10 largest carriers dropped their average denial rate from 23.2% to 19.4%, a 3.8-point improvement reflecting genuine industry-wide progress.

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

Insurer performance varies as sharply as state rates.

Note: 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 the vast majority of rejections in 2024. Medical necessity played a minor role.

About three in four denials (77%) arise from paperwork or plan design, not medical judgment. Insurers argue that administrative denials help prevent duplicate billing and fraud. Consumer advocates warn the burden often falls unfairly on patients who submitted claims correctly but get rejected due to insurer processing errors.

Despite 8.8 million denied claims in 2024, very few consumers challenge 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 1 per 10 million denied claims reached external appeal with an independent reviewer

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

Some denied claims are later paid after resubmission without formal appeals. Persistence can pay off even without navigating the formal 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 300% across insurers. Plan selection during open enrollment is 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.

Federal transparency rules have improved accountability since 2015. Yet 2024's improvement marks only a partial recovery from persistently high denial rates. High rejection rates persist despite nearly a decade of transparency requirements, suggesting that data alone hasn't been enough to drive meaningful change in insurer behavior.

Some denied claims are later paid after resubmission without formal appeals. Persistence can pay off even without navigating the formal appeals process.

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.

Our Approach

MoneyGeek includes all insurers reporting at least 1,000 claims in plan year 2024, regardless of whether they continued offering plans in 2025. This captures the complete experience of patients who filed claims during 2024, including those covered by insurers that later exited the Marketplace.

Calculation Methods

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

Values were rounded to whole percentages for readability. Plans with suppressed or incomplete reporting were excluded. Our analysis includes insurers with more than 1,000 claims submitted.

Note on claim volumes: 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.

Data 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.

Source: CMS Transparency in Coverage (2026 PUF, Plan Year 2024 Data)