How to Appeal a Denied Insurance Claim
A practical step-by-step process to challenge denied claims, build a strong written appeal, and improve approval odds — including when and how to escalate to external review.
Understand why most appeals fail before they start
The majority of denied claim appeals that fail do so not because the denial was correct, but because the appeal was incomplete, vague, or filed past the deadline. Insurers are not required to approve a poorly documented appeal, and they rarely do. Before you write a single word, understand that your appeal is a formal administrative record — it needs to directly address the stated denial reason with specific evidence, and it needs to arrive within the appeal window printed on your denial letter, which is typically 30 to 180 days depending on your plan type and state law.
Pull the exact denial reason code from your EOB
Your Explanation of Benefits (EOB) contains one or more denial reason codes — these are the official reasons your insurer used to process the claim as denied. Common codes include CO-4 (procedure code inconsistent with modifier), CO-50 (non-covered service), CO-97 (payment included in a previous service), and PR-96 (non-covered charge). Do not appeal against a general description — appeal against the specific code. Look up what that code means in the context of your plan, and your entire appeal should be structured around showing why the denial reason does not apply to your specific claim.
Do this before your next billing call
Run your EOB through the analyzer in 2 minutes
Get a focused review and action checklist based on your claim details before you call insurer or provider billing.
Check My EOB NowGather every document before you write anything
A strong appeal packet typically includes: your denial letter and the EOB for the denied claim; an itemized bill from the provider showing procedure codes, dates, and units; your insurance policy or Summary of Benefits and Coverage (SBC) showing that the service should be covered; clinical notes or a letter of medical necessity from your treating provider if the denial was for medical necessity; any prior authorization approval documentation if one was obtained; and a log of any calls you have made, including dates, representative names, and reference numbers. Missing even one of these elements gives the insurer a reason to return your appeal as incomplete. Request anything you do not already have before the appeal deadline, not after.
Call member services to understand the exact reversal criteria
Before submitting a written appeal, call your insurer member services and ask one direct question: what specific evidence or documentation would be required to reverse this denial? This is not a negotiation call — it is an information-gathering call. Write down the representative name, date, time, and reference number. Ask whether any medical necessity review criteria, clinical guidelines, or policy exclusions were used in the denial decision, and request copies if they were. Some insurers will also tell you which reviewer will handle the appeal, which can help you frame the clinical language correctly.
Structure your written appeal to mirror the denial logic
Your appeal letter should have a clear structure: one paragraph identifying who you are, the claim date, claim ID, and denial date; one paragraph stating the denial reason code and the insurer's explanation; one paragraph explaining specifically why that reason does not apply — citing plan language, medical necessity criteria, or factual errors in the adjudication; and a closing paragraph requesting reversal with written confirmation. Attach your supporting documents and reference each one by name in the letter body. Keep the letter factual and direct. Do not describe your financial hardship or frustration — those are not grounds for reversal. The grounds are policy language and clinical necessity.
Submit through a traceable channel and confirm receipt
Submit your appeal through a channel that creates a record. Most insurers have an online member portal with a secure document upload function — use it and screenshot the confirmation. If mailing, send via certified mail with return receipt. If faxing, keep the confirmation page. The appeal clock starts from the date you submitted, and if the insurer later claims they did not receive it, your proof of submission is the difference between a live appeal and a lapsed deadline. Follow up by phone five to seven business days after submission to confirm the appeal was received, logged, and assigned.
Track the response deadline and escalate if it passes
Federal law under the ACA and ERISA requires insurers to decide urgent care appeals within 72 hours, pre-service appeals within 30 days, and post-service appeals within 60 days. State laws sometimes set tighter deadlines. Mark your calendar. If the insurer misses their deadline, that is a separate violation you can report to your state insurance commissioner. If your appeal is denied again, you have the right to request an external review — an independent review by an organization with no financial tie to your insurer. External reviews under the No Surprises Act and ACA have strong reversal rates for medical necessity and surprise billing disputes.
Request external review if internal appeal is denied
External review is the most powerful tool available to consumers after an internal appeal fails. An independent review organization (IRO) that has no relationship with your insurer evaluates the claim using clinical and policy standards. For most employer-sponsored plans and marketplace plans, you have the right to request external review within four months of your final internal denial. For urgent medical situations, expedited external review is available with a 72-hour turnaround. The insurer is legally bound by the IRO decision. Studies consistently show that consumers who pursue external review win a meaningful percentage of cases — particularly those involving medical necessity, experimental treatment, and out-of-network emergency care.
Document everything as if it will eventually go to a regulator
Keep a complete paper trail from the first denial forward. Save every EOB, every denial letter, every appeal submission with confirmation, and every written response from the insurer. Log every call with date, representative name, and reference number. If external review fails or the insurer behaves improperly — for example, by missing deadlines or misrepresenting your policy terms — you can file a complaint with your state insurance commissioner or with the Centers for Medicare and Medicaid Services (CMS) for marketplace and Medicare plans. These complaints are taken seriously and often prompt faster resolution than continued direct appeals. Your documentation is the evidence those agencies need to act.
Ready to apply this to your own bill?
Upload your EOB and get a claim-by-claim review with an appeal prep plan.
Analyze My EOBNeed outside help?
Use official resources and vetted marketplaces to compare options and escalate appeals.
FAQ
How long do I have to appeal a denied insurance claim?
Most plans require you to file an internal appeal within 180 days of receiving the denial. Urgent care appeals have much tighter windows — sometimes as short as 24 to 72 hours. Check the deadline printed on your denial letter and act before it, not after.
Can I appeal more than once?
Yes. Most plans have at least two levels of internal appeal. After exhausting internal appeals, you have the right to request external review by an independent organization. You generally need to complete internal appeals before accessing external review.
What is the difference between internal and external review?
Internal review is handled by the insurance company itself. External review is conducted by an independent review organization with no financial relationship to your insurer. The insurer is legally bound by the external reviewer's decision, which makes external review a powerful final escalation tool.
Does getting a letter of medical necessity from my doctor help?
Yes, significantly — especially for medical necessity denials. A letter from your treating provider that directly addresses the insurer's denial criteria, references clinical guidelines, and explains why the specific service was necessary for your diagnosis is one of the strongest pieces of evidence you can attach to an appeal.
What if the insurer denies my appeal without explaining why?
Insurers are required to provide a clear explanation of any denial, including the specific plan language or clinical criteria used. If you receive an inadequate explanation, request in writing the full clinical review criteria and policy language used in the decision. You can also file a complaint with your state insurance department, which will prompt a formal insurer response.
Sources & references
This guide is grounded in primary government sources. Verify the details that apply to your specific plan and claim.
- How to appeal an insurance company decisionHealthCare.gov (CMS)
- Internal appeals processHealthCare.gov (CMS)
- External review processHealthCare.gov (CMS)
See our sources and methodology and editorial policy for how this guidance is built and reviewed.
Continue your review path
Next reads selected for this scenario so you can move from diagnosis to action without losing momentum.