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

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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.

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KEY FINDINGS
  • The national denial rate dropped from 22.5% to 19.1% between 2023 and 2024, the first decline in four years. It's a partial recovery from the 2022 high but still above the 16.7% recorded in 2021.
  • Of 46 million in-network claims filed across HealthCare.gov states in 2024, about 8.8 million were denied.
  • Paperwork errors and plan design accounted for 77% of denials. Medical necessity was the basis for fewer than one in four.
  • Hawaii at 26.9% and Alaska at 25.5% had the highest state denial rates. South Dakota at 5.4% had the lowest.
  • Among major national insurers, Oscar Health denied 25.3% of claims and Molina Healthcare denied 22%. UnitedHealthcare, processing 6.4 million claims, cut its rate 15 points from 34.2% to 19.1%.
  • Fewer than 0.2% of denied claims went to internal appeal. Policyholders who did appeal won 56% of the time.

First Sustained Improvement Since 2021

From 2021 through 2023, the national denial rate held in a 20% to 23% band with no meaningful movement. The 3.4 percentage point drop in 2024 (a 15% relative decline) marks the first year the trend broke downward.

States with limited insurer competition continue to post the highest rejection rates, and the gap between best and worst remains wide. Alabama cut its denial rate by 15 points, the largest state improvement in 2024. Montana and North Dakota each dropped more than 10 points.

Five states went the other direction. Alaska's five-point climb put it at the second-highest denial rate in the country.

Biggest State Shifts (2023 to 2024)

1
Alabama
33.9%
19%
–14.9
⬇ Improved
2
Montana
24.5%
12.2%
–12.3
⬇ Improved
3
North Dakota
20.8%
9.7%
–11.1
⬇ Improved
4
Texas
23.8%
18.8%
–5
⬇ Improved
5
Indiana
18.5%
15.8%
–2.7
⬇ Improved
6
Mississippi
19.4%
17.5%
–1.9
⬇ Improved
7
Missouri
17%
15.1%
–1.9
⬇ Improved
8
Michigan
14.5%
12.8%
–1.7
⬇ Improved
9
Iowa
21.6%
20%
–1.6
⬇ Improved
10
North Carolina
20.5%
19.4%
–1.1
⬇ Improved
11
Arizona
18.6%
17.4%
–1.2
⬇ Improved
12
Ohio
19.6%
18.7%
–0.9
⬇ Improved
13
Nebraska
18.6%
18.5%
–0.1
⬇ Improved
14
South Carolina
16.2%
16%
–0.2
⬇ Improved
15
Utah
18.9%
18.7%
–0.2
⬇ Improved
16
Wisconsin
11.7%
11.5%
–0.2
⬇ Improved
17
Arkansas
16.3%
15.9%
–0.4
⬇ Improved
18
Tennessee
21.1%
20.7%
–0.4
⬇ Improved
19
Wyoming
17.2%
17.6%
0.4
⬆ Worsened
20
Kansas
17.9%
18.4%
0.5
⬆ Worsened
21
Oklahoma
16.5%
17%
0.5
⬆ Worsened
22
Florida
23.2%
23.5%
0.3
⬆ Worsened
23
Oregon
10.7%
11%
0.3
⬆ Worsened
24
South Dakota
5.2%
5.4%
0.2
⬆ Worsened
25
Louisiana
17.3%
18.4%
1.1
⬆ Worsened
26
West Virginia
17.1%
21.3%
4.2
⬆ Worsened
27
Delaware
15.9%
19.5%
3.6
⬆ Worsened
28
Hawaii
23.7%
26.9%
3.2
⬆ Worsened
29
Alaska
20.4%
25.5%
5.1
⬆ Worsened

Major Insurers Show Mixed Performance

Blue Cross Blue Shield of Montana posted the largest improvement, dropping 27 percentage points from 39.4% to 12.5%. UnitedHealthcare's 15-point decline is more consequential given its volume of 6.4 million claims. Blue Cross Blue Shield of Alabama improved 16 points, falling from 34.8% to 19%.

Oscar Health and Molina Healthcare went the other direction. Oscar Health's seven-point increase brought it to 25.3%, the highest denial rate of any major national insurer. Molina Healthcare added three points to cross the 20% threshold. The 10 largest carriers as a group still improved, cutting their combined average from 23.2% to 19.4%.

Major Insurer Shifts (2023 to 2024)

1
Blue Cross Blue Shield of Montana
39.4%
12.5%
–26.9
⬇ Improved
2
Blue Cross Blue Shield of Alabama
34.8%
19%
–15.8
⬇ Improved
3
UnitedHealthcare
34.2%
19.1%
–15.1
⬇ Improved
4
Blue Cross Blue Shield (aggregate)
21.3%
18%
–3.3
⬇ Improved
5
Cigna Health & Life
22%
19%
–3
⬇ Improved
6
CareSource
20.1%
18%
–2.1
⬇ Improved
7
Anthem / Elevance
19.7%
18%
–1.7
⬇ Improved
8
Medica
18.8%
18%
–0.8
⬇ Improved
9
Molina Healthcare
19%
22%
3
⬆ Worsened
10
Oscar Health
18.4%
25.3%
6.9
⬆ Worsened
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BIGGEST SHIFTS BY STATE AND INSURER
  • Most improved state: Alabama (-15 points)
  • Most worsened state: Alaska (+5 points)
  • Other large improvements: Montana (-12 points) and North Dakota (-11 points)
  • Largest insurer drop: Blue Cross Blue Shield of Montana (-27 points)
  • Highest denial rate among major insurers: Oscar Health (25.3%)

State-Level Denial Rates

At the state level, denial rates in 2024 spanned 5% to 27%, a fivefold gap between the best and worst performers. Hawaii and Alaska are at the top, and South Dakota and North Dakota are at the bottom. Insurer count doesn't determine outcomes: Florida and Texas both exceeded the national average with 11 and 14 competing carriers in their markets.

ACA Claim Denial Rates by State (Plan Year 2024)

1
Hawaii
26.9%
5.2
1.4
16.2%
2
Alaska
25.5%
7.4
1.9
22.2%
3
Florida
23.5%
4,650
1,090
20.2%
4
West Virginia
21.3%
53.7
11.4
21.8%
5
Tennessee
20.7%
854
176
20.7%
6
Iowa
20%
70.5
14.1
21.3%
7
Delaware
19.5%
32.4
6.3
28%
8
North Carolina
19.4%
2,080
405
21.5%
9
Alabama
19%
259
49
19%
10
Texas
18.8%
33,300
6,260
21.6%
11
Ohio
18.7%
277
51.9
20%
12
Utah
18.7%
188
35.2
18.8%
13
Nebraska
18.5%
94.7
17.5
21.3%
14
Louisiana
18.4%
272
50
18.1%
15
Kansas
18.4%
92.6
17.1
19.7%
16
Wyoming
17.6%
14.4
2.5
17.6%
17
Mississippi
17.5%
224
39.2
21.1%
18
Arizona
17.4%
275
47.8
21.2%
19
Oklahoma
17%
840
143
22.9%
20
South Carolina
16%
1,040
167
20.1%
21
Arkansas
15.9%
185
29.5
15.9%
22
Indiana
15.8%
123
19.4
18.1%
23
Missouri
15.1%
216
32.6
19.9%
24
Michigan
12.8%
328
42.1
19.9%
25
Montana
12.2%
89.7
10.9
11.5%
26
Wisconsin
11.5%
328
37.7
10.8%
27
New Hampshire
11.1%
41.1
4.6
17.6%
28
Oregon
11%
33.2
3.7
10.2%
29
North Dakota
9.7%
23.6
2.3
13.5%
30
South Dakota
5.4%
36.6
2
4.1%
—
National Average
19.1%
46,000
8,780
17.8%

Which Insurers Reject Claims Most Often

Among the 10 largest carriers, denial rates ranged from 18% to 25%, matching the variation seen at the state level. Oscar Health denied one in four claims at 25%. UnitedHealthcare had the highest claim volume at 6.4 million and denied 20%, a rate that would have been 34% a year earlier.

1
Oscar Health
7
620
157
25%
2
Molina Healthcare
12
1,900
418
22%
3
Ambetter (Celtic)
10
2,300
481
21%
4
UnitedHealthcare
20
6,400
1,280
20%
5
Cigna Health & Life
14
2,800
532
19%
6
Blue Cross Blue Shield (aggregate)
30
15,000
2,700
18%
7
Medica
6
190
35
18%
8
CareSource
4
210
38
18%
9
Anthem / Elevance
9
500
88
18%
10
Highmark BCBS
2
38
7.4
20%

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

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NOTABLE YEAR-OVER-YEAR SHIFTS (2023 TO 2024)
  • Blue Cross Blue Shield of Montana: 39.4% to 12.5% (-27 points)
  • UnitedHealthcare: 34.2% to 19.1% (-15 points)
  • Blue Cross Blue Shield of Alabama: 34.8% to 19% (-16 points)
  • Oscar Health: 18.4% to 25.3% (+7 points)
  • Molina Healthcare: 19% to 22% (+3 points)

Most Denials Aren't About Medical Necessity

Administrative issues and coverage disputes made up nearly two-thirds of 2024 rejections. Medical necessity determinations were the basis for fewer than one in four. Put another way, 77% of denied claims were turned away not because a doctor said no, but because of paperwork or how the plan is designed.

Insurers say administrative denials catch duplicate billing and fraud. Consumer advocates say the system penalizes patients who filed correctly and got rejected anyway because of errors on the insurer's side.

Administrative (missing info, duplicate, late filing)
40%
Coverage or Eligibility (excluded service, limit reached, member not covered)
25%
Prior Authorization / Referral
12%
Medical Necessity (non-behavioral)
7%
Medical Necessity (behavioral)
2%
Other / Unspecified
14%

Few Consumers Challenge Denied Claims

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.

Why Denial Rates Matter During Open Enrollment

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.

Steps to Take When Claims Get Denied

When claims are denied:

  1. 1
    Request a written explanation

    within 30 days of the denial

  2. 2
    File an internal appeal

    within 180 days (check your specific plan's deadline)

  3. 3
    Escalate to an external review

    if the internal appeal is denied

  4. 4
    Keep detailed documentation

    (claim numbers, appeal letters, denial explanations and all correspondence)

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.

Methodology: How MoneyGeek Analyzed ACA Claims Data

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

Every insurer reporting at least 1,000 claims in plan year 2024 is included, whether or not that insurer continued offering plans in 2025. This preserves the full claims experience of patients covered during 2024, including those whose insurer later left the Marketplace.

How We Calculated Rates

Three metrics were calculated for each insurer and state:

  • Weighted denial rates: claims denied ÷ claims received, weighted by claim volume
  • Median issuer rate per state: the middle value when insurers are ordered by denial rate
  • National insurer averages: combined rates for insurers reporting across multiple states

All values are rounded to whole percentages. Plans with suppressed or incomplete reporting are excluded. CMS publishes claim counts as raw numbers; MoneyGeek converts them to thousands in tables (5,200 in a table = 5.2 million actual claims). Totals cover in-network, post-service medical claims only. Pharmacy and stand-alone dental claims are excluded.

Limitations

The analysis is limited to HealthCare.gov states. The 13 states that run 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.

About Nathan Paulus

Nathan Paulus, Head of Content and SEO, MoneyGeek

Nathan Paulus is Head of Content and SEO at MoneyGeek, where he leads content strategy and produces original data research across insurance, consumer costs, transportation safety, housing, public policy and personal finance. He also reviews published studies for methodology, source quality and factual accuracy before they reach readers.

Research and Analysis

In nearly six years at MoneyGeek, Paulus has published more than 100 original studies and explanatory guides. His insurance research includes 50-state comparisons of health care outcomes, costs and access; an analysis of how uninsured rates track with state Medicaid expansion decisions and electoral patterns; full coverage auto rate analyses across major insurers in all 50 states; and a study of how premium trends track with industry underwriting losses, with combined ratio data sourced from Fitch Ratings, AM Best and Bureau of Labor Statistics CPI figures. His research also covers vehicle pricing trends across the U.S. new car market, summer traffic fatality rates by state, homeowner underinsurance ratios using mortgage and policy data, and housing affordability across all 50 states.

His research has been cited by Bloomberg, the Los Angeles Times, Forbes, Fast Company, the San Francisco Chronicle, USA Today and NBC Los Angeles. Harvard, MIT, Stanford and Yale have also referenced his work.

Career

Growing up, Paulus developed an early interest in personal finance through his grandmother, who emphasized saving over earning as the foundation of financial stability. Her framing still shows up in how he writes about money for people without a financial background.

Paulus joined MoneyGeek in July 2020 as Director of Content Marketing. In that role, he led the content team and directed data journalism production across insurance and personal finance verticals. He was promoted to Head of Marketing and Communications in December 2023, where he took on digital PR and communications strategy. He has held his current role as Head of Content and SEO since January 2025.

Before MoneyGeek, he served as Director of Content Marketing and SEO at Ventrix Advertising. There, he helped build two content sites from scratch, contributed to link-building programs that secured more than 1,500 unique referring domains within a year, and co-managed a marketing team of more than 20 people. Earlier, he spent two and a half years at ABUV Media, moving up from Marketing Research Analyst to Senior Marketing Tactics Analyst, where he built his grounding in audience research, content strategy and SEO.

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