How to appeal a denied health insurance claim

Why most denials never get appealed

According to Kaiser Family Foundation analysis of HealthCare.gov plans, insurers denied roughly 19% of in-network claims and 37% of out-of-network claims in 2024. Yet fewer than 0.2% of denied claims were appealed internally. Among the small share that did appeal, about 44% were overturned at the first internal level, and an additional 27% were overturned through external review.

In other words: the consumers who do appeal win more often than most people assume. The problem is that the process is unfamiliar, the deadlines are tight, and the denial letters are written in jargon that obscures what to do next.

Step 1 — Read your denial letter carefully

Three things on the denial letter matter most:

1. The denial reason. Usually a one- or two-line narrative plus a code (often a CARC code such as 50, 197, or 204). The category of denial drives the appeal strategy.
2. The appeal deadline. Usually 180 days from the date you received the notice. Calendar it the day you read it.
3. The submission method. Insurers usually accept appeals by fax, mail, or member portal. Some have specific forms; others accept a written letter. The letter will tell you.

Step 2 — Identify the denial category

Most denials fall into one of these categories. The category drives what evidence will help.

• Administrative or coding error — wrong code, missing modifier, duplicate, missing information. Often resolvable by your provider’s billing office.
• Prior authorization missing or exceeded — service required prior approval that wasn’t obtained or has been used up.
• Medical necessity — insurer determined the service wasn’t medically necessary based on what they had.
• Plan exclusion — service is not covered under your plan’s terms.
• Out-of-network — provider was outside the plan’s network. Surprise-billing protections may apply.
• Experimental or investigational — treatment is considered not yet proven. Evidence of FDA approval and treatment guidelines helps here.
• Coordination of benefits — primary versus secondary insurer ordering issue.
• Timely filing — claim filed too late by the provider. Usually a provider-side issue.

Step 3 — Gather your evidence

What helps varies by category. Some staples:

• For medical necessity denials: letter from your treating provider explaining clinical reasoning, relevant clinical notes, peer-reviewed studies, and references to treatment guidelines from professional societies.
• For prior authorization denials: proof the process was attempted, evidence of urgent circumstances if applicable, or a statement from your provider that the service was needed before authorization could be obtained.
• For plan exclusion denials: reading the relevant plan language carefully — sometimes the exclusion does not actually apply to your specific service.
• For out-of-network denials: evidence of in-network unavailability, emergency, continuity-of-care, or No Surprises Act protections.

Step 4 — Write a structured appeal letter

A strong appeal letter contains, at minimum:

• Clear identification of the claim being appealed (member ID, claim number, date of service, provider).
• A short statement of facts.
• A direct response to the insurer’s stated denial reason.
• Citations to specific plan-language sections where applicable.
• A clear request — what specifically you want the insurer to do.
• A signature block with contact information.
• An attachment list of supporting documents.

Keep it tight, professional, and dated. Two to four pages is typical. Save a copy of everything you send.

Step 5 — Submit before the deadline and confirm receipt

Use the submission method stated on the denial letter. If faxing, send with a cover sheet that says “URGENT: APPEAL — RESPONSE REQUIRED” and your member ID. Call to confirm receipt within a week of sending.

Step 6 — If denied again, request external review

If your internal appeal is upheld (denied), you generally have the right to external review under the ACA. The external-review organization is independent of your insurer, and its decision is binding. State deadlines for requesting external review typically run 4 to 6 months from the final internal denial. The application usually involves a brief written request and the relevant documents.

When to consider professional help

For administrative and prior-authorization denials, most consumers can file successfully on their own — especially with their provider’s billing office helping. For medical necessity denials, experimental/investigational denials, and high-dollar specialty drug denials, a structured appeal that includes plan-language citations and peer-reviewed support substantially improves your case.

We built InsureDefense to do exactly this — read your denial, identify the category, and prepare a professionally-structured appeal with the evidence patterns that work for your specific situation. Upload your denial for a free triage; we’ll tell you which category you’re in and what your case will need before you decide whether to engage us.

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