5 Reasons Insurance Companies Deny Claims (And How to Fight Back)

Getting an insurance claim denied is frustrating, confusing, and often feels unfair. But here is what most people do not know: insurance companies deny claims constantly, and most denials can be successfully challenged. Industry data consistently shows that a large proportion of denied claims that go through formal appeals are eventually paid — when the appeal is properly filed with the right documentation. Understanding why your claim was denied is the first and most important step to overturning it.

Why Insurers Deny Claims

Insurance companies operate claims handling departments under financial pressure to limit payouts. Denials are driven by algorithmic claim reviews, narrow policy interpretations, and clinical reviewers who may not have examined you. Five denial reasons account for the vast majority of cases.

Pre-existing condition exclusions are applied aggressively. Insurers often designate symptoms, risk factors, or routine check-ups as "evidence" of a pre-existing condition. Under the ACA, most health plans cannot deny coverage for pre-existing conditions — but grandfathered plans, short-term plans, and some employer self-funded plans may still apply these exclusions.

"Not medically necessary" determinations are the most common denial reason for health insurance. Insurers apply their own clinical criteria — often more restrictive than standard physician practice — and conclude that a treatment, procedure, or hospital stay was not essential. They frequently second-guess treating physicians by citing internal coverage policies rather than published clinical guidelines.

Prior Authorization Denied: How to Appeal" class="auto-link">Prior authorization failures occur when treatment was obtained without the required advance approval, or when the authorization process had a paperwork or coordination error. These denials are often procedural rather than clinical — meaning the treatment itself may be covered, but a process requirement was not followed.

Out-of-network billing disputes arise when you receive care from a provider or facility not in your plan's network, often without realizing it. The No Surprises Act (effective 2022) provides significant new protections against unexpected out-of-network bills in emergency situations.

Policy exclusions and benefit limitations are provisions written into your policy that limit or eliminate coverage for specific treatments, conditions, or circumstances. Insurers sometimes apply these exclusions incorrectly, overly broadly, or to situations the exclusion was not intended to cover.

How to Appeal an Insurance Denial

Step 1: Get the Denial in Writing and Read It Carefully

Request your full denial letter and EOB)" class="auto-link">Explanation of Benefits (EOB) if you do not already have them. Your denial letter must state the specific reason for denial, the clinical criteria or policy provision relied upon, and your appeal rights and deadlines. Do not proceed without understanding the exact stated reason — your appeal must directly address it.

Step 2: Request Your Complete Claim File

For ERISA employer plans, you have a legal right under 29 C.F.R. § 2560.503-1 to obtain all documents, records, and other information relevant to your claim, including internal reviewer notes and the clinical criteria applied. For individual health policies, request the specific clinical policy guideline the insurer used. Reviewing these documents often reveals errors or overreach in the denial.

Step 3: Gather Strong Clinical Documentation

Ask your treating physician to write a detailed letter of medical necessity that directly addresses the insurer's stated denial reason. Reference published clinical guidelines — such as those from the American Heart Association (AHA), American Cancer Society (ACS), or relevant specialty societies — that support your treatment. If your insurer cited its own internal clinical policy, compare it to the published guidelines and identify discrepancies.

Step 4: Write a Targeted Internal Appeal Letter

Submit a written appeal that addresses the denial reason point by point, attaches your physician's letter and supporting medical records, cites applicable clinical guidelines, and — for health plan appeals — identifies any federal or state law protections that apply. ACA-compliant plans must cover essential health benefits regardless of internal clinical policies that conflict with these requirements.

Step 5: Request a Peer-to-Peer Review

For medical necessity denials, ask your treating physician to request a peer-to-peer call with the insurer's medical reviewer. Many denials are reversed at this stage when a treating clinician speaks directly with the reviewer and presents clinical context that was missing from the paperwork review.

Step 6: Escalate to External Independent Review: Complete Guide" class="auto-link">External Review or State Regulators

After exhausting internal appeals, request independent external review. Under the ACA, most health plans must offer external review — and external reviewers overturn insurer decisions in a significant percentage of cases. You can also file a complaint with your state insurance department, which creates regulatory pressure and a formal record.

What to Include in Your Appeal

• Complete denial letter with the specific denial reason, clinical criteria cited, and policy provision referenced
• Explanation of Benefits (EOB) identifying the denied service and amount
• Treating physician's detailed letter of medical necessity specifically addressing the insurer's denial reasoning
• Relevant medical records, specialist notes, diagnostic results, and treatment history supporting the claim
• Published clinical guidelines (AHA, NCCN, ADA, APA, or other relevant specialty organization) supporting the denied treatment

Fight Back With ClaimBack

Insurance denials are rarely final — they are the beginning of a process that, when properly navigated, results in claim payment in the majority of cases. Understanding the five most common denial reasons and responding to each with targeted evidence and legal citations is the proven path to overturning a wrongful denial. ClaimBack generates a professional appeal letter in 3 minutes.

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Related Reading

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs External Insurance Appeal