10 Most Common Reasons Insurance Claims Are Denied

The insurer's reviewing physician determined the treatment doesn't meet their clinical criteria for medical necessity. This is the most common denial and often the most challengeable — insurers' internal criteria frequently lag behind established clinical guidelines.

Letter of Medical Necessity from your treating physician + peer-reviewed clinical evidence (NCCN guidelines, AHA guidelines, published studies). The treating physician's direct clinical judgment carries significant weight against a reviewing physician who has never examined you.

The procedure required pre-approval from the insurer before it was performed, and that approval was either not sought or denied. This includes situations where the treating provider failed to obtain authorization.

Request retrospective authorization with urgency documentation. If the procedure was medically urgent, cite emergency exception provisions. If your provider failed to obtain auth, the provider may bear responsibility — escalate to your state insurance commissioner.

The provider who treated you was not in your insurer's approved network, resulting in either full denial or significantly reduced coverage. A common source of surprise medical bills.

Cite the No Surprises Act (effective 2022) for emergency care or situations where in-network care was unavailable. Request network adequacy exceptions and continuity of care protections if you were mid-treatment when a provider left the network.

The insurer argues your condition existed before your coverage began, often used for short-term or non-ACA plans. ACA marketplace plans cannot deny claims based on pre-existing conditions.

Document precisely when the condition was diagnosed versus when your policy started. For ACA plans, cite 42 U.S.C. § 300gg-3 which prohibits pre-existing condition exclusions. For non-ACA plans, review your policy's exact look-back period language.

The claim was denied because required documentation — such as a referral, prior authorization, or medical records — was missing or incomplete at the time of submission.

Resubmit immediately with complete records. Request a list of exactly what documentation is required. This type of denial is often the easiest to overturn — it is administrative, not clinical.

The insurer claims the service is specifically excluded from your policy. Common exclusions include cosmetic procedures, certain dental treatments, and some mental health services.

Request the exact policy language of the exclusion in writing. Challenge whether the exclusion actually applies to your specific procedure. Many exclusions are written broadly and misapplied. Cite mental health parity laws if applicable (Mental Health Parity and Addiction Equity Act).

The insurer classifies the treatment as experimental or investigational, meaning it is not yet considered standard of care by the insurer's criteria — even if widely used by clinicians.

Submit clinical trials evidence, peer-reviewed studies, and FDA approval status. If the treatment has a breakthrough designation or is included in NCCN guidelines, cite these prominently. Many state laws require coverage of routine costs for clinical trial participants.

The insurer flagged your claim as a duplicate of one already processed. This may be an error if the original claim was denied or if the same service was legitimately provided twice.

Provide proof this is not a duplicate, including original claim numbers, service dates, and provider invoices. If the first claim was denied rather than paid, explicitly document that and clarify you are not seeking double payment.

The specific provider — even if employed by an in-network facility — was not individually credentialed by your insurer. Common in hospital settings where individual physicians may not be network participants.

For emergency care, cite emergency care exceptions under state law and federal regulations. For non-emergency care, request continuity of care provisions and escalate to your state insurance department if the provider should have been in-network.

The claim was not submitted within the insurer's required filing window — typically 90 to 365 days from the date of service. Late claims are routinely denied on procedural grounds.

Document any extenuating circumstances (hospitalization, medical incapacity, insurer error) that prevented timely filing. Request a deadline waiver citing your specific circumstances. Many states require insurers to consider extenuating circumstances.