How to Appeal a Denied Health Insurance Claim

By Andrew Ullmann · Last updated July 30, 2026

Documents you need

Before you do anything, make sure you have your denial letter and your EOB. You will need the reason codes to tell you whether you are fighting a clerical denial or a judgment denial.

A clerical denial is often fixed by the provider resubmitting a corrected claim.
A judgment denial often needs a written internal appeal commonly within 180 days (check your plan documents). If upheld, an independent external review will be required. This review is legally binding on the insurer.

Read the denial before you fight it

A denial is not a verdict. It's a starting point. It consists of a form letter with a reason code on it. This code decides your entire strategy. You'll find it in two places: the denial letter and your explanation of benefits (EOB). Your EOB is the statement your insurer sends showing what it paid, what it didn't, and why. If you are having trouble reading your EOB, decode it first with how to read an EOB.

Every denial falls into one of two buckets, and they get fixed in completely different ways:

Denial reason on the EOB or letter	Bucket	First move
Wrong or outdated policy/ID number	Clerical	Provider corrects and resubmits the claim
Coordination of benefits - which of your two plans pays first	Clerical	Update your COB info with the insurer, then resubmit
Coding mismatch on the claim	Clerical	Provider reviews the codes and resubmits
"Not medically necessary"	Judgment	Internal appeal, anchored by your treating provider's letter
No prior authorization	Judgment	Ask the provider about retroactive authorization, then appeal
Out-of-network	Judgment	Check No Surprises Act protections first, then appeal

Bucket 1: clerical denials - fix, don't fight

Plenty of denials are paperwork, not judgment. The claim went in with an old member ID. Your insurer thinks another plan should pay first (e.g. coordination of benefits, the process for deciding which plan pays when you're covered by more than one). Or the procedure and diagnosis codes on the claim don't line up, so the system denied it.

None of these need an appeal. They need a corrected claim. The provider's billing office submits claims all day; a resubmission is routine for them. Call and say:

"My claim for [date of service] was denied - my EOB shows reason [code]. It looks like a submission issue on the claim, not a coverage decision. Can you correct and resubmit it, and put my balance on hold until it's reprocessed? The claim number is [number]."

If it's a coordination-of-benefits denial, also call your insurer and tell them which plan is primary. Then confirm the provider resubmits. Two phone calls, both logged with date, name, and reference number.

Bucket 2: judgment denials - this is the real appeal

Three denials mean the insurer made a decision, not a typo:

"Not medically necessary." The plan is disputing that the care was needed. This is the one where your treating provider carries the clinical argument - more below.
No prior authorization - the plan's advance sign-off wasn't obtained. Ask the provider's office whether they can request authorization retroactively, and appeal in parallel.
Out-of-network. Before you appeal, check whether the care was actually protected - emergency care and out-of-network providers at in-network facilities fall under the No Surprises Act, which changes the fight entirely.

For these, you appeal in writing. Plans must offer an internal appeal, and members commonly get 180 days from the denial to file - but that window is set by your plan, so check your denial letter and plan documents. Submit as soon as possible. Don't burn the clock.

What goes in a strong internal appeal?

Five things, assembled like a case file:

The facts. Claim number, member ID, date of service, provider, what was denied, the reason code. Make it effortless to look up.
The plan language. Find the section of your plan documents that covers this service and quote it back, with the specific page number and quoted section. Insurers argue from the plan document; so should you. If you've never read yours, start with what your health insurance actually covers.
A letter of medical necessity from your treating provider. You don't write the clinical argument - your provider does. Call their office, tell them the denial reason, and ask for a letter of medical necessity supporting the appeal. This letter is the spine of a medical-necessity appeal.
Supporting records your provider's office identifies as relevant.
A clear ask. Overturn the denial and reprocess the claim. AND if they won't, ask them to hand you the tools for round two.

The letter itself can be short. The skeleton:

[Date]

[Plan's appeals address, from the denial letter]

Re: Appeal of denied claim - Member [name], ID [number], Claim [number], Date of service [date]

I am appealing your denial of [service] on [date], denial reason [code or text]. My plan covers this service: "[quote the relevant plan language]" ([document name, page]). Enclosed are a letter of medical necessity from my treating provider, supporting records, and the EOB. I request that the denial be overturned and the claim reprocessed. If you uphold the denial, please provide the specific plan language you relied on and instructions for requesting independent external review.

[Signature, phone, mailing address]

Send it by a trackable method (usually certified mail) and keep copies of the whole packet.

What if the care is urgent?

Urgent cases can get expedited review. If waiting out a standard appeal would jeopardize your health (which is your treating provider's call to document, not yours to argue) request an expedited appeal and ask your provider's office to support the request. The denial letter or plan documents explain how to invoke it.

What happens if the internal appeal fails?

You move to a second, better appeal: external review. After an upheld denial, you can request an independent external review - decided by reviewers outside your insurance company - and the decision is binding on the insurer. The insurer that denied you does not get the last word.

Your upheld-denial letter should include external-review instructions; if it doesn't, demand them in writing. Urgent cases can be expedited here too.

What if my plan is through work?

If your employer self-funds its plan - the company pays claims itself and the insurer just administers - the plan follows federal ERISA rules rather than state insurance law. The playbook is the same, but the rulebook is the plan document. Ask HR for it (often called the summary plan description) and follow the appeal process it lays out, deadlines included.

Where can I get help?

Your state insurance department. This is for state-regulated plans. They take complaints and many run consumer help lines that walk you through appeals.
The marketplace or your plan's member line. This is for marketplace plans. Start with the help line on your card.
HR or your benefits administrator. This is for employer plans. They can pull the plan document and confirm the process.
An attorney, when the sum is large - consider consulting one; legal aid is free for many people.

Track everything

Appeals are won on paper and lost in memory. For every call: document the date, the time, who you spoke to, what was said, and the reference number. For every letter: make a copy, ensure there is proof it was sent and received (often through certified mail). Keep one folder - physical or digital - with the denial, the EOB, the plan language, the provider's letter, and your appeal. When you escalate, that folder does the arguing for you.

The fastest free way to do all of this

Everything in this guide you can do yourself - that's why we wrote it down. Candid builds the appeal for you, for free. Upload the denial and your insurance documents and it identifies the grounds, drafts the appeal letter addressed to your insurer's appeals department (including the demand for the plan language and records the denial relied on) and then watches the clock for you. Your 180-day filing window and the insurer's response deadline are both tracked, for free. It even gives you a little nudge when it's time for external review.

Candid is our tool - this guide is complete without it. It just turns an afternoon of paperwork into a few minutes.

FAQ

How long do I have to appeal a denied health insurance claim?

Commonly 180 days from the denial for the internal appeal, but the window is set by your plan - check the denial letter and your plan documents. Clerical fixes and resubmissions have their own timing, so move early either way.

Who writes the letter of medical necessity?

Your treating provider. They make the clinical case, because they're the one with the medical judgment and your chart. Your job is everything around it: the plan language, the deadlines, the delivery, and the follow-up.

What if my appeal is denied again?

Request independent external review. It's decided outside your insurer and the result is binding on the insurer. NOTE: Urgent cases can get expedited review. Your upheld-denial letter should include the instructions; if not, demand them in writing.

Can someone handle the appeal for me?

Many plans let you authorize a representative - a family member, your provider's office, or an advocate - to appeal on your behalf. Check your plan documents for the authorization form. You still review and sign what matters.

Is a denied claim the same as a surprise bill?

No - different fights. A denial is your insurer refusing to pay under the plan's terms, which you appeal. A surprise bill is an out-of-network provider billing beyond your in-network share in a protected situation, which the No Surprises Act handles.

This guide is general information about medical billing and insurance processes - not legal, medical, or financial advice.