I want to start with a number. Just one.
Two percent.
That is the share of UnitedHealth Group’s total claims volume captured in the federal data that journalists, researchers, and members of Congress have been using to hold the company accountable. Two percent. The other 98%, employer-sponsored plans, Medicaid managed care contracts, Medicare administrative business, exists in a reporting black hole that UHG is not required by law to illuminate.
UHG covers more than 70 million Americans.
And here is the thing: UHG is not alone. Cigna covers roughly 14 million people. Elevance Health (the parent company of Anthem Blue Cross Blue Shield) covers 46 million. Together, these three companies insure approximately 130 million Americans. The public data we have on all of them is a sliver. The rest is protected, proprietary, and invisible.
That is not an oversight. That is a structural advantage. And before we get to the numbers we do have, I want you to hold onto that fact. Because this article is not just about what these companies do with denied claims. It is about what they are allowed to hide. And who decided they could hide it.
What the data shows (and what it doesn’t)
Federal transparency rules require insurers selling plans on the ACA (Affordable Care Act) marketplace to report claim denial data publicly. CMS collects Medicare Advantage prior authorization data. Congressional investigations have produced additional detail. But employer-sponsored insurance, which covers nearly two-thirds of Americans, has no equivalent public reporting requirement. Neither does Medicaid managed care.
The ACA requires group health plans to disclose claims denial data, but those requirements have still not been implemented at the federal level. The Trump administration has also indicated that federal mental health parity regulations requiring employer plan denial data collection will not be enforced.
So, we are left with the marketplace data. And even that tells a story worth reading carefully.
For ACA marketplace plans in 2024, the average in-network denial rate was 19%, ranging from 8% at Elevance Health to 25% at Oscar Health. UnitedHealthcare came in at 20%. Cigna at roughly 17%. These numbers sound like a market functioning within a reasonable range. They are not. They are the best-case window into companies whose full denial picture remains hidden.
UnitedHealth Group: the volume problem
UHG is the largest private insurer in the country. It processed 6.4 million ACA marketplace claims in Plan Year 2024, more than any other insurer, denying 20% of them, down from 33% in 2023.
For Medicare Advantage, UHC’s prior authorization denial rate is 12.8%, the highest among major MA insurers. And for post-acute care specifically, UHC’s denial rate surged from 10.9% in 2020 to 22.7% in 2022, coinciding with deployment of the nH Predict AI algorithm: a tool that estimated recovery timelines using historical population data rather than the actual clinical assessment of the treating physician. Its skilled nursing facility denial rate in 2022 was nine times higher than it was in 2019.
When those Medicare Advantage denials are appealed, approximately 80.7% are overturned. Four in five. Wrong from the start.
Yet fewer than 0.2% of denied claims are ever appealed, roughly 17 appeals per 10,000 denials. A lawsuit against UHG states directly that the company continues using its flawed AI model — with an estimated 90% error rate — precisely because it knows only a tiny minority of policyholders will ever appeal. A federal judge reviewing that claim described the appeals process as “futile.”
When confronted with ACA data showing a 33% denial rate, UHG called the findings “grossly misleading” because the data represents just 2% of their total claims volume. They were right about the sample size. They were not right to use that fact as a shield. They hold the rest of the data. They choose not to share it.
Cigna: 1.2 seconds per denial
If UHG’s story is about volume and algorithms, Cigna’s is about speed.
A ProPublica and Capitol Forum investigation found that Cigna medical reviewers (allegedly physicians) blocked payment for certain tests and procedures by automatically labeling them “not medically necessary” spending an average of 1.2 seconds reviewing each case. In two months, Cigna doctors refused to pay 300,000 claims using this system, called PXDX.
1.2 seconds. Not per page of a medical record. Per claim. Per patient. Per denial.
Cigna also owns EviCore, the largest prior authorization outsourcing company in the country, covering about 100 million consumers, roughly one in three insured Americans. ProPublica found that EviCore uses an AI algorithm its insiders call “the dial,” which can be adjusted to increase denial rates, and operates under risk-based contracts that reward the company financially for keeping claims below set thresholds. Cigna built a subsidiary whose business model is to deny care on behalf of every major insurer in the country. Then it licensed that subsidiary to its competitors.
In Medicare Advantage, Cigna’s prior authorization appeal overturn rate is 86% — meaning 86% of the denials it issues, when challenged, are found to be wrong. Congress asked directly whether Cigna’s PXDX system was leading to patients paying out-of-pocket for care that should have been covered. Cigna did not provide data to refute that conclusion.
Elevance Health: the quiet denier
Elevance, (the company formerly known as Anthem, now operating Blue Cross Blue Shield plans across 14 states) receives far less public attention than UHG or Cigna. The data suggests it deserves more.
Anthem Blue Cross Blue Shield denial rates have ranged between 20% and 30% depending on plan and region. In Medicare Advantage, Elevance’s prior authorization appeal overturn rate is 71.1%, meaning nearly three in four appealed denials are reversed. Elevance requests prior authorizations at a rate of 3.1 per member per year creating a volume of review requirements that burdens providers and delays care before a single denial is even issued.
In ACA marketplace plans for 2024, Elevance’s denial rate was 8% which is the lowest among large insurers. That number is genuinely better. It is also the only number Elevance is required to share publicly. What happens inside their employer-sponsored plans which cover the vast majority of their 46 million members remains unreported.
The appeal trap, across all three
The pattern repeats regardless of which insurer you look at.
Across all major Medicare Advantage insurers in 2023, the majority of appealed prior authorization denials — roughly 4 in 5 — were overturned. That overturn rate is the most honest number in healthcare insurance data. It tells you what the insurer already knew when it issued the denial.
Yet less than 1% of people appeal denials, and when they do, the original denial is upheld 66% of the time on ACA marketplace plans. The gap (14%) between the Medicare Advantage overturn rate and the ACA marketplace appeal success rate tells you something important: the patients most likely to successfully challenge a denial are the ones with the most institutional support (providers, case managers, advocates) filing on their behalf. Everyone else absorbs the “no.”
UHC gives commercial plan members 65 days to appeal. It’s the shortest deadline in the industry. Aetna, BCBS, and Cigna allow 180 days. Miss the window, and the denial stands permanently regardless of clinical merit.
Close to 60% of patients who received a coverage denial reported it delayed their care. Of that group, nearly half said their health problem got worse in the interim. Those are not administrative inconveniences. Those are medical consequences with names attached to them. Medical consequences that the insurance companies are less liable for than if a healthcare provider delivered the same type of delay.
The float: money that works while claims wait
All three companies benefit from the third mechanism, and none of them are required to disclose it.
When premiums are collected and claims are not yet paid, that money earns investment returns. Every day a claim sits in review — whether through a denial, a prior authorization request, an appeal process, or slow processing — is a day that money works for the insurer instead of reaching the hospital or physician who delivered the care.
UnitedHealth’s days claims payable was 47 days at year-end 2024. The company reported $3.651 billion in investment and other income in just the first three quarters of 2024. Cigna and Elevance report similar investment income lines in their annual filings. None of them break out the portion attributable to float on unpaid claims. None of them are required to.
Denials extend float. Appeals extend float further. Requests for additional documentation extend float. The system does not need to be designed with this in mind for it to function this way. It just needs to be slow. And it is slow by design.
What we cannot see — and why that is the real story
I want to be precise about what this article can and cannot prove.
The ACA marketplace data and Medicare Advantage data are real, sourced from federal filings and congressional investigations. The Cigna PXDX findings come from ProPublica’s documented reporting with internal company spreadsheets. The float mechanism and investment income figures are from SEC filings. Every number in this article has a source.
But the complete picture (denial rates across all plans, all members, all lines of business for UHG, Cigna, and Elevance) does not exist in any public dataset. Employer-sponsored plans covering most Americans under 65 have no equivalent federal reporting requirement. A patchwork of state laws exists, but none apply to self-funded employer plans, which cover the majority of privately insured Americans.
Together these three companies insure roughly 130 million people. The publicly available denial data covers a fraction of that. The rest is protected, proprietary, and invisible by law, by design, and by the continued failure of Congress to require otherwise.
A 2025 KFF poll found that more than half of U.S. adults believe closer regulation of insurers’ decisions to approve or deny claims should be a “top priority” for Congress. That poll also found that the federal government has not used the available claims denial data to conduct any oversight of insurers, nor to develop any tools to help consumers compare plans based on denial behavior.
Our legislative representatives are making healthcare policy: cutting Medicaid, restructuring Medicare Advantage, fighting over the No Surprises Act. They are doing this without the most basic information about how the largest insurers in the country actually operate. The debate is happening in the dark, deliberately, for the benefit of the companies that benefit most from the darkness.
That needs to change. Comprehensive, standardized, public denial reporting across all lines of insurance business, not just ACA marketplace plans, should be a floor. Not an aspiration. Not a future rulemaking. A floor.