Quick Answer: Oscar Health denies the most claims among major national insurers, rejecting roughly 25 percent of in-network claims according to 2026 CMS data analyzed by KFF. Molina Healthcare follows at about 22 percent. This data covers Affordable Care Act marketplace plans only, not employer-sponsored coverage, and most denials are administrative rather than medical necessity decisions.
Choosing a health plan by premium alone leaves out the question that matters most when you actually get sick. Will this company pay the claim? Federal data shows the answer depends heavily on which insurer you pick, with denial rates ranging from about 6 percent to 25 percent among major national carriers.
Our research team analyzed the 2026 CMS Transparency in Coverage dataset alongside KFF’s independent analysis of the same federal filings. This guide ranks the major insurers by denial rate, explains what the numbers actually cover, and shows you what to do if your own claim gets denied.
What the 2026 Data Actually Measures
The Centers for Medicare and Medicaid Services requires insurers selling Affordable Care Act marketplace plans to report claims data every year. This is the only large-scale, federally mandated denial rate dataset publicly available for health insurance.
The figures in this guide cover in-network, post-service claims for Plan Year 2024, reported to CMS in 2025 and analyzed in 2026. Post-service means the claim was filed after care was already delivered, not a prior authorization request made in advance. Understanding this scope matters, since a company’s true claim behavior includes categories this dataset does not capture.
2026 Insurer Denial Rate Ranking
Denial rates vary sharply across major national insurers, based on the same federal reporting period.
| Insurer | ACA Marketplace Denial Rate | Notes |
|---|---|---|
| Oscar Health | About 25% | Highest among major national insurers |
| Molina Healthcare | About 22% | Well above the roughly 19% national average |
| Ambetter (Centene) | About 20 to 21% | High marketplace enrollment volume |
| UnitedHealthcare | About 19 to 20% | Down sharply from about 33% in the 2023 data |
| Blue Cross Blue Shield (aggregate) | About 18% | Aggregate figure hides wide variation by state affiliate |
| Kaiser Permanente | About 6% | Lowest among major national insurers |
Source: KFF analysis of CMS Transparency in Coverage data, Plan Year 2024, published 2026.
Reviewing rates like these matters just as much as comparing what you would pay out of your own pocket. Our guide to health insurance out-of-pocket costs covers the other side of that budget question.
Why the Blue Cross Blue Shield Number Is Misleading
The 18 percent Blue Cross Blue Shield figure looks moderate compared to Oscar or Molina. That single number hides more than it reveals.
Blue Cross Blue Shield is not one company. It is a federation of 36 independent, separately operated licensees, each running its own claims adjudication system and applying its own medical necessity criteria. State-level BCBS denial rates in recent data have ranged from below 10 percent to above 34 percent depending on the specific licensee.
If your plan comes from a Blue Cross Blue Shield affiliate, the national aggregate tells you almost nothing useful. What matters is your specific state licensee, which you can look up separately in the CMS public dataset.
What Actually Causes Most Health Insurance Company Denials
A high denial rate sounds like insurers refusing care to sick patients. The federal data tells a different story for most rejected claims.
KFF’s review of 2024 marketplace data found that only about 5 percent of denials were attributed to a lack of medical necessity. The largest categories were an unlisted “other” reason at 36 percent and administrative reasons at 25 percent, followed by missing prior authorization or referral at 9 percent. In plain terms, most denials trace back to paperwork, coding, and process failures rather than a doctor’s recommended treatment being rejected outright.
This does not make denials harmless. A denied claim still leaves a patient with an unexpected bill and a confusing appeal process, regardless of the underlying reason.
What This Data Does Not Tell You
Treat these numbers as one important input, not the full picture of an insurer’s behavior. Several real limits apply.
- The data covers Affordable Care Act marketplace plans only. It excludes employer-sponsored coverage, which insures a larger share of Americans under 65.
- Medicare Advantage plans are not included and report denial data through a separate CMS process.
- Pre-service claims, including prior authorization requests denied before care was delivered, are not part of this dataset.
- The figures reflect a single reporting year and can shift as insurers adjust their processes and risk pools.
If your coverage comes through an employer rather than the marketplace, these specific percentages will not apply directly to your plan.
How to Check Your Own Plan Before You Enroll
You are not limited to the national averages in this guide. The underlying CMS data is public and searchable by individual insurer and state.
Search the CMS Transparency in Coverage public use file or the KFF summary tables for your specific state and insurer before open enrollment. National rankings can differ meaningfully from the rate your specific state licensee reports, particularly for Blue Cross Blue Shield and other regionally operated carriers.
What to Do If Your Claim Is Denied
A denial is a starting point, not a final answer. Federal rules give you a clear path to challenge it.
- Read the denial letter carefully to identify the specific reason code the insurer cited.
- Ask your doctor’s office to review and resubmit the claim if the issue was a coding or paperwork error.
- Request your claim file from the insurer, which must be provided within 30 days of your request.
- File a formal internal appeal within the deadline stated in your denial letter, typically within six months.
- If the internal appeal fails, request an external review through your state or the federal Department of Health and Human Services process.
Fewer than 1 percent of denied claims are ever appealed, even though many administrative denials can be resolved through resubmission alone. Persistence has a real chance of success. Families managing rising costs on top of denial risk may also want to review how much health insurance premiums are rising in 2026 before choosing a plan for the coming year.
Frequently Asked Questions
Does a high denial rate mean an insurer is bad?
Not automatically. A high denial rate signals more friction in the claims process, but most denials stem from administrative and coding issues rather than a company refusing necessary care. Weigh denial rates alongside network access, customer service, and your own healthcare needs before ruling out an insurer.
Does this data include employer health plans?
No. The denial rates in this guide come from Affordable Care Act marketplace filings only. Employer-sponsored plans report under different rules and are not included in this specific CMS dataset, so these percentages do not describe employer coverage.
What is the difference between an administrative denial and a medical necessity denial?
An administrative denial results from paperwork, coding errors, or missing prior authorization, not a judgment about your treatment. A medical necessity denial means the insurer determined the specific treatment did not meet its coverage criteria. Federal data shows administrative reasons account for far more denials than medical necessity does.
How often do appeals succeed?
Success rates vary by claim type and insurer. Federal data shows insurers uphold their original denial in a majority of internal appeals, but administrative denials, which make up most rejections, are generally the easiest to resolve through resubmission or a straightforward appeal.
Which company has the lowest denial rate?
Kaiser Permanente reports the lowest denial rate among major national insurers, at approximately 6 percent of in-network marketplace claims. Its integrated model, where the insurer and the care provider operate under one organization, is often cited as a reason for its lower denial rate.
Choosing an Insurer Means Weighing More Than the Premium
Oscar Health and Molina Healthcare report the highest claim denial rates among major national insurers in the 2026 federal data, while Kaiser Permanente reports the lowest. These figures cover ACA marketplace plans only, and most denials trace back to administrative causes rather than medical necessity decisions.
Check your specific state insurer’s rate before enrolling, keep your denial letter and claim file organized if a rejection happens, and remember that an initial denial is rarely the final word.
This guide provides general insurance education only. Denial rates reflect Affordable Care Act marketplace data for a single reporting year and may not represent your specific plan, state, or employer-sponsored coverage. Consult your insurer, your state insurance department, or a licensed insurance professional for guidance on your specific situation.
Content reviewed: July 2026. Figures reflect CMS Transparency in Coverage data for Plan Year 2024, reported in 2025 and analyzed by KFF in 2026.
