We Analyzed 10,847 Insurance Claim Denials. Here's What We Found.

The Data Behind 10,847 Insurance Claim Denials

Insurance companies deny claims. Everyone knows this. What almost nobody knows is the pattern behind those denials — which reasons are most common, which countries have the worst Denial Rates by Insurer (2026)" class="auto-link">denial rates, and critically, which types of denials are most likely to be overturned on appeal.

At ClaimBack, we've processed tens of thousands of appeal letters across four countries. What follows is an honest analysis of what those cases reveal. We're sharing this because patients, journalists, and healthcare advocates deserve real data — not insurer marketing materials.

The Top Denial Reasons, Ranked

Across 10,847 denied claims in our dataset (US, UK, Australia, Singapore; 2024–2025), the breakdown by primary denial reason is:

"Not medically necessary" is the dominant denial category by a wide margin. It is also, notably, the most subjectively applied — medical necessity determinations involve clinical judgment, and insurer-employed reviewers are not always better positioned than treating physicians to make that call. This category also has the highest appeal overturn rate, as we discuss below.

Country Patterns: Where Denials Are Most Common

The denial experience differs substantially by country, driven by regulatory structure, insurer market concentration, and the strength of consumer complaint mechanisms.

United States

The US has the most complex denial landscape in our dataset. Employer-sponsored plans governed by ERISA (Employee Retirement Income Security Act of 1974) have different appeal rights than individual marketplace plans under the Affordable Care Act (ACA). Key patterns:

• ACA marketplace plans have External Independent Review: Complete Guide" class="auto-link">external review rights guaranteed under 45 CFR Part 147 — but 40% of eligible consumers in our dataset did not use them.
• Mental health and substance use disorder denials are disproportionately high relative to the Mental Health Parity and Addiction Equity Act (MHPAEA) compliance obligations that should limit such denials.
• Prior authorisation denials have surged since 2020, driven by insurer cost-containment programs that Congress has begun to address via proposed legislation (the Improving Seniors' Timely Access to Care Act).

The Kaiser Family Foundation (KFF) has separately documented that 60% of appealed ACA plan denials result in the insurer reversing their decision — a figure that underscores how many initial denials are unjustified.

United Kingdom

NHS-adjacent private health claims in the UK are governed primarily by the Financial Conduct Authority (FCA) under the Insurance: Conduct of Business Sourcebook (ICOBS). UK private health insurance (PHI) denial rates are lower in absolute terms than the US, but:

• Exclusion-based denials are disproportionately common — UK PHI policies tend to have broader exclusion language than equivalent US or Australian policies.
• The Financial Ombudsman Service (FOS) upholds consumer complaints in approximately 38% of PHI cases — meaning insurers are routinely wrong in a substantial share of the cases that reach escalation.
• Moratorium underwriting disputes (where coverage of conditions depends on a symptom-free period before policy inception) are a distinctly UK pattern not reflected in other markets.

Australia

Australia's PHI system operates under the Private Health Insurance Act 2007 (Cth), which provides a more structured regulatory environment than the US. Key data points:

• Waiting period denials are the single most common dispute type referred to the Private Health Insurance Ombudsman (PHIO) — reflecting how frequently the 12-month pre-existing condition rule is misapplied.
• PHIO received over 11,000 complaints in its most recently published annual report, with funds reversing their decisions in a meaningful proportion of investigated cases.
• The Australian Competition and Consumer Commission (ACCC) has noted that PHI policy complexity contributes to consumer misunderstanding — a finding that correlates with our data showing documentation and exclusion-related denials are elevated in the AU market.

Singapore

Singapore's Integrated Shield Plan (ISP) market — where MAS-regulated private riders sit atop MediShield Life — shows a distinct pattern:

• Pre-authorisation failures are the leading denial cause for ISP claims, reflecting the structured referral requirements that took effect from the 2021 ISP framework reforms.
• Medically necessary treatment denials are clustered in a narrow set of procedure types — spinal, bariatric, and psychiatric — suggesting systematic insurer review policies rather than case-by-case clinical judgment.
• MAS Notice 120 creates binding procedural obligations on ISP insurers that, when violated, provide independent grounds for appeal success beyond the substantive merits of the claim.

Which Denial Types Have the Highest Appeal Success Rates?

This is the question that matters most to anyone holding a denial letter.

Incomplete documentation denials are the most reversible. These are administrative failures — often on the provider's side, not the patient's — and fixing them requires little more than resubmitting with the correct paperwork. Yet a significant portion of patients accept these denials without acting.

Prior authorisation denials have a surprisingly high overturn rate when patients appeal. This is partly because post-service PA denials (where treatment has already been delivered and the insurer retroactively objects to the authorisation process) are on legally thin ground in many jurisdictions. The No Surprises Act in the US, for example, added new constraints on retroactive PA denials for emergency services.

Medical necessity denials are worth fighting with clinical support. The 54% overturn rate climbs substantially when the appeal includes a detailed letter from the treating physician specifically addressing the insurer's denial language and criteria.

Exclusion-based denials are the hardest to reverse — but not impossible. Policy language is often ambiguous, and courts and ombudsmen regularly find in favour of consumers when insurers apply exclusions in ways that the reasonable policyholder would not have anticipated.

The 60% Statistic Every Patient Should Know

The KFF study of ACA marketplace denials — the most rigorous publicly available analysis of US insurance denial patterns — found that 60% of appeals result in the insurer overturning the original denial. Six in ten.

That number has significant implications. It means the majority of appealed denials were wrong to begin with. It means the initial denial is not a considered final judgment — it is frequently a first-pass automated or cursory review. And it means the single most actionable thing any denied claimant can do is file a formal written appeal.

The obstacle is not the odds. The obstacle is that writing a good appeal letter is time-consuming, unfamiliar, and emotionally draining at a time when most people are already stressed. That's the gap ClaimBack exists to fill.

What This Means If You Have a Denied Claim

The data points in one direction: appeal. The majority of denials that are challenged are resolved in the consumer's favour. The ones that are accepted without challenge are accepted permanently.

A quality appeal letter — one that cites the specific denial grounds, the relevant regulatory framework, the supporting clinical evidence, and the insurer's own obligations — dramatically outperforms a generic complaint. Insurers review thousands of appeals. Letters that demonstrate regulatory literacy and specificity get different treatment than form letters.

ClaimBack generates regulation-specific insurance appeal letters at https://claimback.app. Answer questions about your denial, and receive a professionally structured letter in minutes — tailored to your country, your insurer, and the specific grounds for your denial.

Methodology Note

The 10,847 cases in this analysis were drawn from ClaimBack user-submitted denial data across 2024–2025. Cases were classified by primary denial reason as stated in the insurer's denial letter. Appeal overturn rates are based on reported outcomes from users who submitted appeal letters and subsequently reported results. Country-level regulatory data is drawn from publicly available PHIO, FOS, CMS, and MAS published statistics. The KFF appeal overturn rate is sourced from the Kaiser Family Foundation's published ACA marketplace research.

We publish this data because patients deserve to understand the landscape they're navigating. Share it with anyone who needs it.