How to Appeal an Insurance Denial: A Patient Guide

August 18, 2026 | 10 min read | LegitMedBilling Team

A denial letter is written to sound final. It is not. Insurers deny claims for reasons that range from genuine coverage decisions to a missing digit on a form, and a large share of denials are overturned when someone actually challenges them. This guide is about how to do that properly — and it is written by people who appeal denials for a living, from the provider side.

First, Find Out What Was Actually Denied

Do not start writing until you know the real reason. The denial letter gives a summary; the explanation of benefits gives the code. Those two often say different things, and the code is the one that matters, because it tells you which of three very different situations you are in.

Type of denial	What it means	Difficulty
Administrative	Missing prior authorisation, wrong member ID, eligibility mismatch, filed late	Often fixed with a phone call
Coding	The service was covered but billed with a code the plan did not accept	Usually the provider's to fix
Medical necessity	The insurer says the service was not needed	A genuine appeal — and winnable

This distinction saves enormous effort. If it is a coding or administrative problem, the fastest route is your provider's billing office, not an appeal letter — they can correct and resubmit the claim, often within days. Only a medical necessity or coverage denial genuinely needs you to appeal.

You Have Two Levels of Appeal, and Most People Use One

Under the Affordable Care Act, plans must give you a full and fair internal appeal — the insurer reviews its own decision. If it upholds the denial, you then have the right to an external review by an independent body with no relationship to the insurer, whose decision is binding on the insurer.

That second stage is the most underused right in health insurance. People receive the internal appeal rejection, read it as the end of the road, and pay. It is not the end of the road. The reviewer at external review has no commercial interest in the outcome, which is precisely why it is worth reaching.

If waiting would seriously jeopardise your health, ask for an expedited appeal, typically decided in around 72 hours. In urgent situations you can often request an expedited internal appeal and an expedited external review simultaneously rather than running them in sequence.

The Deadline That Ends Appeals Before They Start

You generally have 180 days from the denial notice to file an internal appeal. That sounds generous and it disappears quickly, because the useful evidence — medical records, the physician's letter, the plan's own coverage criteria — takes weeks to assemble and the clock does not pause while you gather it.

Request two things in the first week: your complete claim file from the insurer, which you are entitled to, and the specific plan language the denial relied on. Insurers must tell you the rule they applied. Once you can see it, you can often show the service does meet it.

What to Put in the Letter

Identify the claim precisely. Name, member ID, claim number, date of service, provider. A letter that cannot be matched to a claim goes nowhere.

Quote their reason back to them. Use the exact wording and code from the denial notice, so there is no ambiguity about what you are appealing.

State plainly why it is wrong — the authorisation existed, the coverage applies, the service was necessary. One or two sentences.

Attach the evidence. Records, test results, and a letter of medical necessity from your doctor. That physician letter is the highest-value document in the whole file.

Send it traceably and keep a copy of everything, with a log of every call: date, name, reference number.

Keep it short and factual. Appeals are decided on documentation, not on tone, and a two-page letter with strong attachments beats ten pages of frustration every time.

Ask Your Provider to Help — They Want This Too

Your provider is not on the other side of this. When your claim is denied, they usually have not been paid either, so their billing office has a direct interest in the appeal succeeding. They can supply records, correct a coding error, and write the medical necessity letter.

Tell them in writing that the claim is under appeal and ask them to hold the account rather than send it to collections. Most will. Meanwhile, if you are also disputing the amount itself, our guides on disputing a medical bill and negotiating a hospital bill cover that separate track, and hospital charity care is worth checking — many people qualify without knowing.

If the denial concerns a bill from a provider you did not choose at a facility you did, the No Surprises Act may protect you outright. And if the service was denied for lack of prior authorisation, our prior authorization guide explains how that process is supposed to work.

Frequently Asked Questions

Can I appeal if my insurance denies a claim?

Yes. If your plan is covered by the Affordable Care Act you have a legal right to a full internal appeal, and if the insurer upholds the denial you have a further right to an independent external review by a reviewer not employed by the insurer. Those rights exist regardless of what the denial letter implies.

How long do I have to appeal an insurance denial?

Generally 180 days from the date of the denial notice for an internal appeal. Do not wait - request the full claim file early, because gathering records takes longer than people expect and the deadline does not pause while you collect them.

What is an external review?

An independent review by a body with no relationship to your insurer, available after the internal appeal is exhausted. The decision is binding on the insurer. It is the single most underused patient right in health insurance, and a meaningful share of denials are overturned at this stage.

What is an expedited appeal?

A fast-tracked appeal used when waiting would seriously jeopardise your health or your ability to regain function - typically decided in around 72 hours. You can often request an expedited internal appeal and an expedited external review at the same time rather than waiting for one to finish.

What should I include in an appeal letter?

Your name, member ID, claim number and date of service; the specific reason given for denial, quoted from the letter; why that reason is wrong; and evidence - the medical records, a letter of medical necessity from your doctor, and the plan language that supports coverage. Keep it factual and short.

Which denials are most often overturned?

Administrative and coding errors are the easiest, because the service was covered and the claim was simply wrong - a missing prior authorisation number, a coding mismatch, an eligibility error. Medical necessity denials are harder but far from hopeless, particularly with a strong letter from the treating physician.

Do I have to pay the bill while I appeal?

You should not be pushed into paying a disputed amount while an appeal is open. Tell the provider's billing office in writing that the claim is under appeal and ask them to hold the account. Most will, because they want the insurer to pay rather than chase you.