How to Appeal a Health Insurance Claim Denial Successfully

The Numbers, and Who Is Quoting Them

Search this topic and you will find appeal success rates quoted between 44% and 80%. The spread is not noise — it depends on which market, which denial type and which source, and the highest figures come predominantly from companies that sell appeal services.

Here is what the federal transparency data actually shows, from KFF's analysis of CMS reporting on HealthCare.gov marketplace plans:

Prior authorization denials do better still. Reporting covering 2025 shows appeals overturning 67% of prior authorization denials in Medicare Advantage, 47% in Medicaid managed care and 43% in the federally facilitated Marketplace.

Two honest caveats. External review outcomes are genuinely not well measured — the marketplace data is suppressed at small values, so anyone quoting a precise national external overturn rate is extrapolating. And self-funded employer plans, which cover most insured Americans, are not required to report denial data publicly at all, so the national picture is unknown rather than known.

What is not in doubt: roughly one in five in-network claims is denied, almost nobody challenges it, and close to half of those who do are proved right.

Start With the Reason Code, Not the Letter

The single most useful thing you can do is establish why the claim was denied, because the four main reasons need completely different responses.

Your Explanation of Benefits carries a standardised reason code. Find it before writing anything.

Filing a full clinical appeal against what is actually a coding typo wastes weeks. Call the provider's billing office first and ask whether the codes submitted match the care delivered. A corrected claim resolves a surprising share of denials without any appeal at all.

Ask for Two Documents

Before drafting anything, request these from the insurer in writing. Both are things you are entitled to and neither is volunteered.

The full case file, including the internal medical reviewer's notes. The EOB gives you a phrase; the reviewer's notes give you the actual reasoning, and you cannot rebut an argument you have not read.

The clinical policy bulletin the decision relied on — the specific internal guideline, with its version and date. Insurers apply written criteria, and those criteria are sometimes years out of date relative to current practice. A policy dated several years ago being used to call an established treatment experimental is a straightforward argument, and asking for the document by name changes the conversation.

The Deadlines

Under the Affordable Care Act, for non-grandfathered plans:

• Internal appeal: 180 days from the denial notice. Miss it and you generally forfeit the right to external review as well.
• External review: typically four months after the final internal denial.
• Expedited appeals exist where delay would seriously jeopardise your health, with decisions commonly required within 72 hours. You can request an expedited internal appeal and external review simultaneously in urgent cases.

Phone calls do not pause any of these clocks. A verbal assurance that ""it's being looked at"" is worth nothing, so follow every call with a written summary through the member portal or by certified mail, noting the date, the representative's name and the reference number.

Writing the Appeal

Precision beats volume. Reviewers work through queues, and a focused submission is read; a hundred pages of undifferentiated records is skimmed.

Include:

1. The denial reason, quoted, with the claim number and dates of service.
2. A letter of medical necessity from your physician stating the diagnosis, the treatment history, why the denied treatment is indicated for you specifically, and the clinical risk of not receiving it.
3. Only the relevant records — the imaging, the exam notes, the lab results that speak to the denial reason. Nothing else.
4. Evidence that the treatment is established, where the denial says experimental: FDA approval, and its place in current specialty clinical guidelines.
5. Documented failure of required alternatives, where step therapy is cited — which medications were tried, when, and what happened. Failures from years earlier still count if they are in your records.

Address the specific reason given. An appeal arguing that the treatment helped, against a denial that says step therapy was not completed, does not engage with the decision.

External Review Is a Real Right, Including on Employer Plans

If the internal appeal fails, you can take the case to an Independent Review Organization — third-party clinicians with no relationship to the insurer. The insurer is bound by the outcome.

One correction to advice you will still see: this is not limited to individual market plans. Non-grandfathered self-funded employer plans governed by ERISA are subject to external review too, through a federal process. If you are told your only remaining option is litigation, ask specifically about the federal external review process before accepting that.

Internal appeals are free. External review may carry a nominal filing fee in some states, commonly waived for financial hardship or refunded if you win.

Only 3% of upheld internal appeals go on to external review, which means the overwhelming majority of people stop one step before an independent clinician looks at the file.

Emergency and Out-of-Network Bills

The No Surprises Act protects you from balance billing in two situations: emergency services, and care from an out-of-network provider at an in-network facility — the anaesthetist, radiologist or assistant surgeon you never chose.

In both cases your responsibility is limited to what you would have paid in-network. If you are billed the difference, the protection is statutory rather than discretionary, and citing it by name in writing usually resolves it. See handling out-of-network charges in emergencies and what to do about a very large medical bill.

Appeal and Grievance Are Different Things

An appeal challenges a coverage decision. A grievance complains about conduct — a delay in authorisation, a representative giving wrong information, an unreturned call.

Where both apply, file both. Insurers report grievance volumes to regulators, and a complaint to your state insurance department puts a regulatory clock on the file that an internal appeal does not. It is free, and it frequently produces movement on cases that had stalled.

Note the jurisdictional split: state regulators oversee fully insured plans, while self-funded employer plans fall under the Department of Labor. Ask your HR or benefits administrator which type yours is, because it determines who to complain to.

Where to Get Help

You do not have to do this alone, and some of the help is free.

Non-profit patient advocacy organisations provide case managers who handle insurance disputes at no cost, particularly for serious diagnoses. Many hospitals employ patient advocates or financial counsellors whose job includes exactly this. Your physician's office may have a prior authorisation specialist who does these appeals routinely and knows what the local payers respond to.

Commercial appeal services exist too and charge a fee or a share of the recovery. They can be worth it for large or complex claims — but note that they are also the source of the highest success rates you will see quoted, so treat their marketing figures accordingly.

Two Situations

The denial that was a typo

A procedure is denied as incidental to another service. The patient prepares a clinical appeal, then calls the provider's billing office first and discovers the submitted code understated the complexity of what was actually performed.

The office submits a corrected claim. It pays without any appeal.

This category is the most common and the least discussed, because it does not feel like a fight. Checking the codes before writing an appeal costs one phone call and frequently ends the matter.

The step therapy denial answered with dates

A specialty medication is denied as non-formulary, with the insurer listing cheaper alternatives that must be tried first.

The patient's records show two of those alternatives were tried years earlier, with documented adverse reactions. The physician's letter of medical necessity sets out each drug, the dates, and what happened.

The denial is reversed, because the insurer's own criterion — that alternatives be tried and fail — had already been satisfied. The appeal did not argue that the rule was unfair. It demonstrated the rule was met.

Both are composite illustrations of common patterns, not accounts of specific individuals.

The Sequence

1. Read the EOB and identify the reason code.
2. Call the provider's billing office to rule out a coding error.
3. Request the full case file and the clinical policy bulletin used, in writing.
4. Diarise 180 days from the denial date.
5. Get a letter of medical necessity addressing the specific denial reason.
6. Submit a focused internal appeal with only relevant records.
7. Request expedited handling if delay would jeopardise your health.
8. Escalate to external review if upheld — including on employer plans.
9. File a grievance and a regulator complaint in parallel where handling has been poor.
10. Keep everything in writing, with dates.

Frequently Asked Questions

How long do I have?

Generally 180 days from the denial notice for an internal appeal under ACA rules, and typically four months after the final internal denial for external review. Check your plan documents, since some plans differ.

Are my chances actually good?

Better than most people assume. Insurers reversed 44% of internal appeals in the marketplace data, and prior authorisation denials are overturned at higher rates still. Fewer than 1% of denied claims are ever appealed.

What is a letter of medical necessity?

A statement from your physician giving the diagnosis, treatment history, why this specific treatment is indicated for you, and the clinical consequences of going without. It is the central document in any medical necessity appeal.

Can I go straight to external review?

Normally you must exhaust the internal process first. Urgent cases are the exception — expedited internal and external reviews can run in parallel.

Does it cost anything?

Internal appeals are free. External review may carry a small filing fee in some states, usually waived for hardship or refunded on success.

What if my plan is through my employer?

You still have appeal rights, and non-grandfathered self-funded plans are subject to a federal external review process. Complaints about self-funded plans go to the Department of Labor rather than a state regulator.

What if the insurer says the treatment is experimental?

Ask for the clinical policy bulletin with its date, then compare it against current FDA approval status and specialty clinical guidelines. Outdated internal criteria are a common and winnable argument.

Should I keep paying the bill while appealing?

Talk to the provider's billing office and ask them to hold the account while the appeal is pending — most will. Ignoring the bill without telling anyone is what leads to collections.

The Short Version

Roughly one in five in-network claims is denied. Fewer than one in a hundred is appealed. And when people do appeal, insurers reverse themselves about 44% of the time — before any independent reviewer is involved.

Before writing anything, find the reason code and call the provider's billing office, because a large share of denials are coding errors that a corrected claim fixes without an appeal. Then request the case file and the clinical policy bulletin the decision relied on, and answer the reason actually given rather than making a general case.

You have 180 days, everything must be in writing, and if the internal appeal fails you can take it to an independent reviewer whose decision binds the insurer — including on an employer plan.

Sources and Editorial Note

Denial rates, appeal rates and internal appeal outcomes are from KFF's analysis of federal transparency data published by CMS for qualified health plans on HealthCare.gov. These figures describe marketplace plans only; self-funded employer plans are not required to report denial data publicly, so national rates across all coverage types are not known. Prior authorization overturn rates reflect KFF analysis of insurer-reported metrics covering 2025. External review outcome data for marketplace plans is suppressed at small values and cannot be reliably stated as a national rate. Appeal deadlines and external review rights derive from the Affordable Care Act and implementing regulations; balance billing protections from the No Surprises Act.

This article describes insurance appeal procedure and is not medical or legal advice. Nothing here should influence treatment decisions, which belong with your clinicians, and a coverage dispute should never delay care you need — speak to your provider about your options if cost is a barrier. Plan terms, deadlines and applicable regulators vary; confirm against your own plan documents, and contact your state insurance department or, for self-funded employer plans, the US Department of Labor.