How to Appeal a Denied Health Insurance Claim (Step-by-Step Guide)
How to Appeal a Denied Health Insurance Claim (Step-by-Step Guide)
By Tatiana Kadetskaya, Insurance Attorney
Your health insurance just denied your claim. Maybe it was a surgery, a medication, a specialist visit, or a procedure your doctor ordered. The denial letter landed in your mailbox or inbox, full of confusing language, and your first reaction was probably some version of: is this it? Is this really how this ends? It's not.
Every year, health insurance companies deny millions of valid claims — and fewer than 0.5% of patients ever appeal. But here's what insurers don't advertise: when people do appeal, 40 to 60 percent of those denials get overturned. That number climbs even higher when the appeal is well-written and properly supported.
I've spent over a decade as an insurance attorney watching people leave thousands of dollars on the table simply because they didn't know they could fight back — or didn't know how. This guide gives you the complete, step-by-step process to appeal a denied health insurance claim, from reading your denial letter to submitting an appeal that insurers take seriously.
Step 1: Read Your Denial Letter Carefully — the Reason Is Everything
The most important thing on your denial letter is not the dollar amount. It's the reason for denial.
Insurance companies are required by law to tell you exactly why they denied your claim. This reason — sometimes called a denial code or denial category — determines your entire appeal strategy. A letter that says "not medically necessary" requires a completely different argument than one that says "out-of-network provider" or "lack of prior authorization." The most common denial reasons you'll see are:
Not medically necessary. The insurer claims the treatment did not meet its clinical criteria, even though your doctor ordered it. This is the most common denial type and one of the most frequently overturned.
Out-of-network provider. The insurer says your provider wasn't in their approved network, or that you should have used an in-network alternative. Many of these denials ignore your legal protections, including the No Surprises Act.
Lack of prior authorization. The insurer claims approval should have been obtained before the treatment. These are common and often overturnable — especially for urgent or emergency care.
Policy exclusion or not covered. The insurer says the treatment falls outside what your plan covers. These denials often rely on vague or broadly interpreted exclusion language that can be successfully challenged.
Experimental or investigational treatment. The insurer labels your treatment unproven. These denials frequently fail to account for recent clinical research and are highly appealable with the right evidence.
Coding errors (CO-167, CO-50, PR-1, CO-197, CO-96). These are administrative denials based on billing and procedure code mismatches, deductible disputes, or data entry errors. Many resolve without a formal appeal once the provider corrects the underlying codes.
Find the denial reason on your letter — it may be listed as a short phrase, a code, or both. If the language is unclear, call the number on the back of your insurance card and ask a representative to explain it to you in plain terms. You are legally entitled to this explanation.
Step 2: Find Your Appeal Deadline and Write It Down Right Now
This is the step most people skip. Don't. Every health insurance plan has strict deadlines for filing appeals. Miss the deadline and your right to appeal is permanently gone — no exceptions, no extensions. Insurers know this, and they are not obligated to remind you.
Most plans give you 180 days from the date of the denial letter to file an internal appeal. Some give only 60 days or 30 days. Employer-sponsored ERISA plans and Medicare Advantage plans can have even shorter windows.
Find the appeal deadline on your denial letter — it's usually buried near the bottom in a section titled "Your Appeal Rights" or "How to Appeal This Decision." Write it down. Set a phone reminder. Then start moving immediately.
If your situation is urgent — if you need the treatment now to avoid serious harm — you may qualify for an expedited appeal. Insurers must respond to expedited appeals within 72 hours. We'll cover that in Step 5.
Step 3: Request the Documents You Need
Before you write a single word of your appeal, you need three things in front of you.
Your full insurance policy and Summary Plan Description (SPD). Most people have never read their policy. Request it directly from your insurer if you don't have it. Under federal law — specifically ERISA for employer plans, and the ACA for marketplace plans — insurers must provide this to you. Read the sections that cover your denial reason: the medical necessity definitions, the exclusion clauses, the network coverage rules.
The clinical criteria used to deny your claim. This is the internal guideline your insurer used to evaluate your treatment. You are legally entitled to see it. Call your insurer and ask for "the clinical coverage criteria or medical policy used to evaluate my claim for [treatment name]." This document is often the key to your appeal — because your job is to show that your treatment meets their own criteria, not just that your doctor recommends it.
Your Explanation of Benefits (EOB). This is the statement your insurer sends showing how your claim was processed. It shows the dates of service, the codes used, the amounts billed, and the reason for denial. Compare it against your actual medical bills and make sure everything matches.
Step 4: Get Your Doctor Fully on Your Side
An appeal without physician support is an appeal with one hand tied behind its back. Your doctor's involvement can be the single most important factor in whether your appeal succeeds.
You need more than a generic "I support my patient's appeal" letter. What you need is a detailed letter of medical necessity that speaks directly to the insurer's denial reason.
Ask your doctor to write a letter that:
States the specific diagnosis and why this particular treatment is medically necessary for your condition
Explains what alternative treatments were tried and why they failed or are not appropriate
Cites relevant clinical guidelines, peer-reviewed research, or specialty society recommendations that support the treatment
Directly addresses the insurer's stated denial criteria and explains why your case meets them
The more specific and clinical the language, the better. A letter that says "this treatment is necessary for my patient's health" will be ignored. A letter that says "this treatment meets the insurer's own criteria for medical necessity as defined in their clinical coverage policy, specifically criteria 2(b) and 3(a)" will be read.
Step 5: Write Your Internal Appeal Letter
This is where most appeals are won or lost.
The internal appeal is your formal written challenge to the insurance company's decision. It goes directly to their appeals department, which is — legally — required to conduct a fresh, independent review of your claim, separate from whoever denied it originally.
A strong appeal letter is not emotional. It is not a story about how much you suffered or how unfair the system is. It is a structured legal and clinical argument that addresses the denial reason point by point, presents your evidence, and demands a specific outcome.
Here is the structure that works:
Opening paragraph. State clearly that you are filing a formal internal appeal of the denial of claim number [X] dated [date], for [treatment/service] provided on [date of service]. State the denial reason as listed in the denial letter. Keep this concise and factual.
Your argument section. This is the core of the letter. Address the insurer's denial reason directly:
If denied as not medically necessary: explain why the treatment meets the insurer's own clinical criteria, cite your doctor's letter, reference applicable clinical guidelines (American Medical Association, relevant specialty societies), and include supporting medical records.
If denied as out-of-network: cite the No Surprises Act if applicable, document that no in-network alternative was reasonably available, reference your state's network adequacy rules.
If denied for lack of prior authorization: explain why authorization was not obtained (emergency, unclear requirements, provider error), document the medical necessity of the care, and cite applicable state or federal protections for urgent care.
If denied as experimental: present peer-reviewed clinical studies, FDA approval status if relevant, guideline endorsements from major medical organizations, and your physician's clinical rationale.
If denied due to a coding error: identify the specific incorrect code, explain what the correct code should be, and request a corrected claim review.
Your evidence list. At the end of the argument section, list every document you are including: medical records from [dates], physician letter of medical necessity dated [date], clinical guidelines from [source], policy document page [X]. Make the reviewer's job easy.
Your closing demand. End with a clear, specific request: "I respectfully request that you overturn this denial and approve coverage for [specific treatment/service]." State that you expect a written response within the legally required timeframe.
Submission details. Send your appeal by every available channel: certified mail (keep the tracking number), fax (keep the confirmation), and through your insurer's online member portal if one exists. Insurance companies have claimed to lose appeals sent by a single method. Multiple channels creates a paper trail that protects you.
Step 6: Know Your Escalation Options If the Internal Appeal Fails
If your internal appeal is denied, you are not out of options. You have at least two more levels of recourse.
Second-level internal appeal. Many plans offer a second internal review. Check your denial letter — if a second appeal is available, use it. Include any additional evidence you've gathered since the first appeal.
External appeal. This is your most powerful tool. An external appeal is reviewed by an independent organization that has no relationship with your insurer. Their decision is legally binding — if they overturn the denial, your insurer must pay. Period. Under the ACA, most health plans must offer external review as a right. In most states, you have 60 days from the internal appeal denial to request one.
State Department of Insurance complaint. Filing a complaint with your state's insurance regulator costs you nothing and puts pressure on the insurer. It also creates a paper trail that can be useful if you pursue legal action.
Legal action. For large claims, particularly those covered by ERISA (most employer-sponsored plans) or those involving bad-faith denial practices, consulting an insurance attorney is worth it. Note that ERISA claims are litigated in federal court under a different standard than state-law claims — which is another reason exhausting your internal and external appeals thoroughly before suing is critical.
The Fastest Way to Write a Winning Appeal Letter
The most common reason appeals fail isn't missing evidence or a weak doctor's letter. It's the letter itself — the wrong structure, the wrong tone, arguing the wrong thing, or simply not knowing what claims reviewers are trained to look for.
This is what attorney-drafted appeal letter templates solve. Instead of starting from a blank page and guessing at the right legal framework, you start with a letter that was built by an insurance attorney who has seen thousands of these reviews from both sides — and knows exactly what moves the needle.
AppealTemplates.com offers attorney-drafted appeal letter templates for every major denial type:
Medical necessity denial — for claims denied as "not medically necessary"
Out-of-network denial — for claims denied because your provider was out of network
Prior authorization denial — for claims denied because pre-approval wasn't obtained
Policy exclusion / not covered — for claims denied as excluded or not covered (our most purchased template)
Experimental or investigational treatment — for claims denied as unproven
PR-1 deductible denial — for claims denied with code PR-1
CO-167 diagnosis/procedure mismatch — for claims denied due to coding mismatch
Each template is editable, comes with a video tutorial walking you through exactly how to customize it, and is available as an instant download. You can have your appeal letter ready to send today.
Not sure which template applies to your denial? Use the Which Appeal Letter Do I Need? guide to find the right one in under two minutes.
And if you want to walk through the full appeal process before you start writing, the Free Appeal Guide covers every step — from reading your denial letter to submitting your appeal — at no cost.
Frequently Asked Questions
How long does a health insurance appeal take? Standard internal appeals must be decided within 30 days for pre-service claims (treatment not yet received) and 60 days for post-service claims (treatment already received). Expedited appeals for urgent care must be decided within 72 hours.
Can I appeal a denial from years ago? Probably not. Most plans strictly enforce appeal deadlines of 30 to 180 days from the denial date. In rare cases — such as mental health parity violations or newly discovered evidence — exceptions exist, but these require legal assistance to pursue.
What if I can't afford to pay the bill while I wait for the appeal? Contact the provider's billing department immediately and explain that you have a pending insurance appeal. Most providers will hold the account, waive late fees, or set up a payment plan while the appeal is in process. Get this agreement in writing.
Do I need a lawyer to appeal a health insurance denial? No — not for most denials. A well-structured appeal letter with strong physician support and proper documentation wins a significant share of cases without any legal representation. An attorney becomes worth consulting when the claim is very large, when all internal and external appeals have been denied, or when you believe the denial violates state or federal law.
What is the difference between an internal and external appeal? An internal appeal goes to your insurance company. An external appeal goes to an independent third-party reviewer whose decision is legally binding on the insurer. You must exhaust internal appeals before requesting external review in most cases.
What if my employer's insurance is denying my claim? Most employer-sponsored health plans are governed by ERISA, a federal law that has its own appeal procedures and legal standards. ERISA plans must follow specific timelines and documentation requirements. If you have an ERISA plan and your internal appeal is denied, the external appeal and any subsequent legal action follow ERISA rules — which is why building a complete, well-documented internal appeal record is especially important.
You Have More Power Than They Want You to Know
The health insurance system is built on the assumption that most people will accept a denial and move on. Fewer than one in two hundred denied patients ever files an appeal. Insurers have structured their denial letters, their phone systems, and their timelines to make the process feel overwhelming enough that you give up. Don't give up.
The law is on your side. Your doctor is on your side. And with the right appeal letter — one that speaks the language insurers respond to — the odds are genuinely in your favor.
Start with your denial letter. Find the reason. Check the deadline. Get your doctor's support. And write an appeal that shows the insurer exactly why they got it wrong.
If you want help with the letter itself, that's what we're here for.
