How to Appeal a Denied Health Insurance Claim (2026 Step-by-Step)

A denied claim is not the final word. It is the start of a process you have the legal right to use — and most people never do.

By the Fight Back editorial team · Banana Bay Press · Updated July 26, 2026

To appeal a denied health insurance claim, read your denial letter to find the exact reason and deadline (usually 180 days), request your full claim file in writing, get a Letter of Medical Necessity from your doctor, and file a written internal appeal before the deadline. If that fails, request a free, independent external review — its decision is binding on your insurer.

Your claim was denied. Here's what that really means.

Getting a denial letter feels final. It is designed to. The language is dense, the reason is often a single vague phrase, and the natural response is to assume the insurer knows something you don't. But a denial is not a verdict — it's a first decision, and the law gives you a clear, structured way to challenge it.

Denials are far more common than most people realize. In 2024, insurers on HealthCare.gov plans denied roughly 85 million in-network claims — about 19% of everything submitted (KFF, 2024). Many of those denials come down to paperwork, coding errors, or missing prior authorization — not a genuine finding that your care wasn't needed. That's exactly the kind of decision an appeal can fix.

Why so few people appeal — and why that's a mistake

Here is the number that should change how you think about your denial: in 2024, HealthCare.gov consumers appealed fewer than 1 in 100 denied claims (KFF, 2024). Insurers upheld about 66% of the internal appeals people did file — which means a meaningful share were reversed, and outcomes are often better still at the external-review stage.

Read that together and the picture is clear. The vast majority of denials are simply accepted. The people who push back are a tiny minority — and a real portion of them win. You don't need to be right about the law or the medicine to start. You need to be one of the few who actually files. Appealing is free, it's built into federal law, and it costs the insurer time and money to keep saying no.

What your denial letter is telling you

Before you can fight a denial, you have to understand it. Your denial notice and your Explanation of Benefits (EOB) contain everything you need to build the appeal:

• The specific reason for the denial. Common ones include "not medically necessary," "experimental or investigational," "out of network," "no prior authorization," or a coding or eligibility error. The wording matters — it tells you what your appeal has to answer.
• The claim number and dates of service. You'll reference these in every letter and phone call.
• Your appeal deadline. This is the most important date in the whole process. Most plans give you 180 days from the notice to file an internal appeal.
• How to appeal. The letter must explain where to send your appeal and what to include.

If the reason is unclear — and it often is — that's your first lever. You have the right to request the plan language and clinical criteria the insurer used, and a vague denial is hard for an insurer to defend on review.

How to appeal a denied claim: 5 steps

The process looks intimidating from the outside, but it's really five steps. Work through them in order and keep a copy of everything.

1. Read the denial letter — find the reason and the deadline. Pull out the exact denial reason, your claim number, and your appeal deadline (usually 180 days). Everything else in your appeal is built to answer that specific reason.
2. Request your claim file in writing. Ask your insurer, in writing, for your complete claim file — including the specific plan provisions and the clinical criteria they used to deny the claim. You're entitled to this at no cost, and it shows you exactly what you need to rebut.
3. Get a Letter of Medical Necessity. Ask your treating provider for a Letter of Medical Necessity that spells out your diagnosis, the treatment, why it's needed, and the guidelines that support it. This is the single most persuasive document in most appeals.
4. File the internal appeal in writing before the deadline. Send a written internal appeal that names the claim, states plainly why the denial is wrong, and attaches your evidence. Submit it before your deadline, keep copies, and get proof of delivery (certified mail or a confirmation number).
5. Escalate to an external review. If the internal appeal is denied, request an independent external review. A reviewer who doesn't work for your insurer looks at your case — and by law, the insurer must accept the outcome.

Internal appeal vs. external review

These are two different stages, and knowing the difference keeps you from stopping too early.

An internal appeal asks your insurance company to look at its own decision again. You file it first, usually within 180 days of the denial. Standard internal appeals are generally decided within 30 days for care you haven't received yet and 60 days for care you already got; urgent cases can be expedited to a matter of days.

An external review is your escalation. If the internal appeal fails, you can send the case to an independent review organization that has no financial stake in the outcome. You typically have four months from the internal denial to request it. The external process is free under the federal system (some state processes may charge up to $25, often waivable), and — this is the part that matters most — the decision is binding. Your insurer is required by law to accept it (HealthCare.gov). Standard external reviews are usually decided within 45 days, and urgent ones within 72 hours.

The takeaway: a "no" on your internal appeal is not the end. For many people, the external review is where a wrong denial finally gets corrected.

Common denial reasons — and how to counter them

Most denials fall into a handful of buckets. Match yours to the list below and aim your appeal at that specific reason.

"Not medically necessary"

This is where a Letter of Medical Necessity does its work. Have your provider connect your diagnosis and history to recognized clinical guidelines and explain why alternatives are inappropriate. Attach the records that back it up.

"Experimental or investigational"

Counter with published evidence, specialty-society guidelines, and your provider's explanation of why the treatment is accepted standard care for your condition — not experimental in your situation.

"No prior authorization" or a coding/paperwork error

These are the most fixable denials of all. Ask your provider's billing office to confirm the codes, correct any errors, and supply the authorization or documentation that was missing. Many of these resolve quickly once the paperwork is right.

Prescription drug denials

Medication denials — step therapy, formulary exclusions, quantity limits — have their own playbook. See our guide on what to do when insurance denies your medication for the exceptions and appeals process specific to prescriptions.

"Out of network"

If in-network care wasn't reasonably available, or the service was an emergency, you may have grounds to challenge the denial or request an exception. Document the lack of an in-network option and any referrals.

Put it in writing — and keep everything

Phone calls are useful for gathering information, but your appeal itself should be in writing. Send it by certified mail or through your insurer's portal so you have proof of the date. Keep a copy of every letter, form, and record, and write down the name and date of every phone call. If your case ever reaches external review or your state insurance department, that paper trail is what makes it easy to say yes.

You don't have to do this alone, and you don't have to be an expert. You can authorize a representative to file for you, and you can lean on your doctor's office for the clinical pieces. The Fight Back guides walk you through each step, and our Insurance Denial Appeal Kit gives you the fill-in-the-blank letters if you'd rather not start from a blank page.