7 Most Common Reasons Insurance Claims Are Denied — And How to Beat Each One

Insurance companies don't deny claims randomly. They rely on a relatively small set of grounds that apply across most claim types and most markets. Once you understand which category your denial falls into, you know exactly where to focus your appeal.

Here are the 7 most common reasons insurance claims are denied — and how to build a strong case against each one.

---

1. "Not Medically Necessary"

This is the most common denial reason for health insurance claims worldwide. The insurer argues that your treatment, test, or procedure didn't meet their definition of "medical necessity" — even though your doctor prescribed it.

Why this denial succeeds (when it does): Insurers often have their own proprietary clinical criteria (such as InterQual or MCG in the USA, or their own internal guidelines elsewhere) that don't align with your doctor's clinical judgment. Without a counter-argument from your treating physician, the insurer's criteria go unchallenged.

How to fight back: Get a targeted letter from your treating doctor — specifically one that addresses the insurer's definition of "medical necessity," cites published clinical guidelines (NICE, MOH, AHFS, Cochrane review evidence), and explains why conservative alternatives were considered and ruled out. Submit this with your appeal. This specific, clinical counter-argument overturns this denial more than any other.

---

2. Pre-Existing Condition Denial

The insurer claims your condition existed before you took out the policy, and therefore falls within a pre-existing condition exclusion.

Why this denial succeeds (when it does): Insurers sometimes apply this exclusion loosely — claiming that any condition with even a remote prior connection to your claim is "pre-existing." Some claimants don't check exactly how their policy defines the exclusion.

How to fight back: Start by reading the exact definition of "pre-existing condition" in your policy. There are usually temporal limits (e.g., "conditions diagnosed within the last 3 years"). Then establish a clear medical timeline: when were you first diagnosed, treated, or symptomatic? Was the condition disclosed when you applied for the policy? If so, the exclusion may not apply. A letter from your GP confirming the diagnosis timeline can be decisive.

---

3. Policy Exclusion

The insurer claims the specific treatment, event, or circumstance falls within an exclusion clause in your policy — so you were never covered.

Why this denial succeeds (when it does): Policy exclusions are real and sometimes clear. But they're also frequently applied more broadly than the policy wording actually supports.

How to fight back: Read the exclusion clause carefully. Does it actually apply to your situation, or is the insurer stretching its scope? Insurance exclusion clauses must be read narrowly. Under the legal principle of contra proferentem, any ambiguity in an exclusion clause is interpreted against the insurer. If there's any reasonable interpretation of the clause that covers your claim, you have grounds to appeal.

---

4. Failure to Obtain Prior Authorisation

The insurer says you should have obtained pre-approval before the treatment — and since you didn't, they won't pay.

Why this denial succeeds (when it does): If your policy genuinely required prior authorisation and you didn't seek it, the insurer has a point. But this denial is often applied unfairly in emergency situations, or where the insurer's own processes made pre-approval impractical.

How to fight back: Was the situation urgent or an emergency? If so, most jurisdictions require insurers to waive prior authorisation requirements for emergency care. Did your doctor try to obtain authorisation? Was the insurer's process unclear or unavailable? Document everything and argue that the denial is disproportionate and inconsistent with the emergency nature of the care. Regulators in many markets (including AFCA and FOS) take a dim view of prior authorisation denials in genuine emergency cases.

---

5. Insufficient Documentation

The insurer claims you didn't provide enough documentation to support your claim — and therefore denied it rather than asking you for more.

Why this denial succeeds (when it does): Some insurers use this as a delaying tactic or an easy first denial, knowing many claimants won't follow up. In some cases, the insurer genuinely needed specific information and didn't communicate this clearly.

How to fight back: This is one of the most straightforward denials to fight. Simply provide the missing documentation, submit it with a formal appeal, and note that the insurer should have requested this information from you before issuing a denial (this is a requirement under most regulatory frameworks, including FCA ICOBS in the UK and AFCA guidelines in Australia). If you're unsure what documentation is needed, ask in writing and document the insurer's response.

---

6. Claim Filed Outside the Policy Period / Waiting Period

The insurer says your claim was filed too late, or that the event occurred during a waiting period.

Why this denial succeeds (when it does): Waiting periods and claim filing deadlines are real policy terms. But insurers sometimes misapply these rules, apply them to the wrong dates, or apply them to conditions that were acquired after the waiting period ended.

How to fight back: Establish the exact dates: when did the policy start, when did the waiting period end, when did the condition or event first arise, and when did you file your claim? Compare these against the exact language in your policy. If the insurer's dates are wrong, or if the condition clearly arose after the waiting period, document this with medical records and submit a formal correction.

---

7. Non-Disclosure or Misrepresentation

The insurer claims you failed to disclose a material fact when you applied for the policy — giving them grounds to void the policy or deny the claim.

Why this denial succeeds (when it does): Genuine non-disclosure — where a policyholder knew about a relevant condition and deliberately failed to disclose it — is a valid ground for denial in most jurisdictions. But this ground is also frequently overused by insurers who apply it to innocent non-disclosure or to facts that weren't material to the underwriting decision.

How to fight back: The key questions are: Was the non-disclosed information genuinely material (would it have changed the insurer's decision to offer you cover at all, or at the same premium)? Was the non-disclosure innocent or deliberate? In many jurisdictions, innocent non-disclosure entitles the insurer to adjust the policy terms — not necessarily void it entirely. Regulators in Australia (Insurance Contracts Act), the UK (Consumer Insurance (Disclosure and Representations) Act 2012), and Singapore have specific rules that protect consumers from heavy-handed application of non-disclosure provisions. Cite these in your appeal.

---

The Common Thread

Every one of these denial reasons can be challenged with the right approach: understand the exact legal or regulatory standard that applies, gather evidence that directly addresses that standard, and present your case in a formal, structured letter that shows you know your rights and are prepared to escalate.

Ready to fight back? Generate your appeal letter free →