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Claims & Billing

How to Appeal an Insurance Claim Denial (And Actually Win)

By the PolicyZen Team · Updated March 2026 · 9 min read

Getting a claim denied feels like hitting a wall. But it's not the end of the road — it's the beginning of a process that you can win more often than you think.

The data is clear: a meaningful percentage of denied claims are overturned on appeal. The reason most people don't win isn't that their case is weak — it's that they don't appeal at all. Most people accept the denial and pay. Insurers count on this.

Why Claims Get Denied: The Most Common Reasons

ReasonWhat It Means
Not medically necessaryInsurer doesn't agree the treatment was required
Missing prior authorizationApproval wasn't obtained before the service
Out-of-network providerProvider not in your plan's network
Service not coveredThe specific treatment isn't in your plan
Coding errorWrong billing code submitted by the provider
Duplicate claimSame claim submitted more than once
Coordination of benefitsYou have multiple plans; insurer disputes who pays first
Policy lapsedCoverage wasn't active on the date of service
Important: Before appealing, check whether the denial is actually a billing or coding error. A surprising number of "denials" are really administrative errors — the wrong procedure code was submitted, a digit was transposed in a member ID, or the service date was entered incorrectly. Call your provider's billing department first. A corrected claim resubmission may resolve it without a formal appeal.

Step-by-Step: How to Appeal

  1. 1
    Get the denial in writing

    Request a written Explanation of Benefits (EOB) or denial letter that states the specific reason for denial and the criteria used. You cannot appeal effectively without knowing exactly why you were denied.

  2. 2
    Read your denial reason carefully

    The denial reason dictates your entire appeal strategy. "Not medically necessary" requires clinical evidence. "No prior auth" may require a retroactive auth request. "Not covered" requires a careful reading of your plan documents. Different reasons need different responses.

  3. 3
    Gather your documentation

    You need: your EOB or denial letter, your policy documents, your medical records relating to the denied service, any supporting clinical evidence (treatment guidelines, peer-reviewed studies), and a letter of medical necessity from your doctor.

  4. 4
    Request a peer-to-peer review

    This is your most powerful tool and most people don't know it exists. Your doctor can call the insurer's medical director directly to discuss the case physician-to-physician. These calls frequently result in reversals. Ask your provider's office to request one immediately.

  5. 5
    File your internal appeal

    Submit your written appeal with all supporting documentation to your insurer before the deadline (typically 180 days from denial for health insurance). Include: a cover letter stating your case clearly, the letter of medical necessity, clinical evidence, and any plan language supporting coverage. Be specific and reference your exact policy language.

  6. 6
    If denied again: request external review

    Under the ACA, you have the right to an independent external review by a third party not affiliated with your insurer. External reviewers overturn insurer decisions at meaningful rates. For urgent medical situations, expedited external review decisions must come within 72 hours.

  7. 7
    Last resort: state insurance commissioner

    If external review fails or isn't available, file a complaint with your state's insurance commissioner. This creates a regulatory record and sometimes prompts insurers to reconsider. For employer-sponsored plans governed by ERISA, your recourse is federal court rather than the state commissioner.

What to Put in Your Appeal Letter

Frequently Asked Questions

How long do I have to appeal?
For health insurance, federal law requires insurers to allow at least 180 days from the denial date to file an internal appeal. Your plan may allow more. Check your denial letter — the deadline should be stated. Missing this deadline waives your right to appeal, so don't delay.
Do I need a lawyer to appeal?
No — most successful appeals are handled by patients and providers without lawyers. A lawyer becomes worth considering for large claims (tens of thousands of dollars) after all administrative remedies have been exhausted, particularly for ERISA plan litigation. For most denials, a well-documented appeal letter and peer-to-peer review are sufficient.
Can my doctor help with my appeal?
Absolutely — and they should. Your doctor can write a letter of medical necessity, provide supporting clinical documentation, and most importantly, request a peer-to-peer review call with the insurer's medical director. Physician involvement significantly improves appeal outcomes. Don't fight this battle alone.
What if I already paid the bill?
You can still appeal — and if you win, your insurer must reimburse you. The timeline still matters, so don't wait. Paying the bill doesn't forfeit your right to challenge the denial.
What is an Explanation of Benefits (EOB)?
An EOB is a document your insurer sends after processing a claim. It shows what was billed, what the insurer paid, what you owe, and if a claim was denied, why. It is not a bill — it's a summary of how the claim was processed. Always review your EOBs carefully. Errors in how claims are processed are common and often correctable.

Understand Your Coverage Before You File

Upload your insurance policy to PolicyZen. Know exactly what's covered — and have the ammunition you need if a claim gets denied.

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