How to Appeal an Insurance Denial: Step-by-Step (With Deadlines)

You've decided to fight back. Good. The data is on your side: 40% to 83% of insurance appeals succeed when patients follow the right process. The insurance company counts on you being confused, overwhelmed, and too exhausted to push back. This guide makes sure that doesn't happen.

Here is the complete process, step by step, with every deadline you need to know.

Before You Start: Understand What You're Appealing

Every appeal starts with understanding the denial. Pull out your denial letter and identify:

1. The denial reason — insurers are legally required to state the specific reason
2. The type of claim — was this a Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization denial, a claim for services already received, or a concurrent review denial during ongoing treatment?
3. Your appeal deadline — write this down now. Missing it is the most common fatal mistake

Common denial reasons include: not medically necessary, prior authorization not obtained, out-of-network provider, experimental/investigational treatment, coverage exclusion, or billing/coding error.

Step 1: Request Your Complete Claim File (Do This First)

Under federal law, you have the right to request all documents related to your denial — including the insurer's internal review criteria, the reviewer's notes, and the clinical guidelines used to make the decision.

Call member services and say: "I am requesting all documents, records, and guidelines used in evaluating and denying my claim, including any utilization review criteria." Keep a record of when you made the request. They must provide this.

This document package often reveals exactly what evidence you need to include in your appeal.

Step 2: Know Your Deadlines — These Are Non-Negotiable

Missing an appeal deadline can permanently waive your right to challenge a denial. Here are the standard timelines:

Employer-sponsored plans (ERISA-governed)

• Internal appeal: 180 days from receiving the denial notice
• External Independent Review: Complete Guide" class="auto-link">External review: 4 months after internal appeal denial
• Expedited internal appeal (urgent care): 72 hours

ACA Marketplace plans

• Internal appeal: at least 30 days (most plans allow 60–180 days)
• External review: 60 days after internal appeal denial
• Expedited review: 72 hours for urgent situations

Medicare

• Part A/B: 120 days for standard appeal (Redetermination)
• Part D (drugs): 60 days
• Expedited: 72 hours

Medicaid

• Varies by state, typically 30–90 days — check with your state Medicaid office

IMPORTANT: These are the federal minimums. Your plan may offer longer windows. Always check your denial letter and plan documents for your specific deadline.

Step 3: Gather Your Evidence

A winning appeal is built on documentation. Here's what you need:

Medical documentation

• Your doctor's letter of medical necessity (the most important document)
• Relevant medical records — office notes, test results, imaging reports, lab work
• Records showing prior treatments attempted and their outcomes

Clinical support

• Peer-reviewed medical literature supporting your treatment
• Clinical practice guidelines from major medical associations (AMA, specialty boards)
• The insurer's own clinical criteria — and how your case meets them

Your personal documentation

• A timeline of your condition and treatment history
• Documentation of any prior authorizations you attempted to obtain
• Records of all phone calls with the insurer (dates, times, rep names)

Step 4: Write Your Appeal Letter

Your appeal letter is the foundation of your case. It should:

• State clearly that you are filing an appeal and reference your claim number and denial date
• Summarize the denial reason and why it is incorrect or incomplete
• Present your medical argument — why the treatment is medically necessary, why alternatives are not appropriate, why the insurer's criteria are met
• Reference specific documents you're attaching (letter of medical necessity, records, literature)
• Request a specific outcome — ask them to reverse the denial and approve the claim

Keep the tone professional and clinical. Avoid emotional language in the formal letter itself — save that for your personal statement. Focus on facts, medical evidence, and the insurer's own criteria.

Your doctor may also write a separate appeal letter or can cosign yours. A letter from your physician carries significant weight.

Step 5: Submit Your Internal Appeal

Submit your appeal through the method specified in your denial letter (usually mail or online portal). Always send via certified mail if mailing — you need proof of delivery.

Keep copies of everything you submit.

The insurer must respond within:

• 30 days for pre-service (prior authorization) appeals
• 60 days for post-service (claims already filed) appeals
• 72 hours for expedited urgent care appeals

Step 6: If the Internal Appeal Is Denied — External Review

If your internal appeal is denied, you have the right to an external independent review under the ACA. This review is conducted by an IROs) Explained" class="auto-link">Independent Review Organization (IRO) with no financial ties to your insurer.

External reviewers override insurer decisions approximately 40% of the time — making this a genuinely powerful tool, not just a formality.

To request external review:

• File within 60 days of your internal appeal denial (4 months for ERISA plans)
• Include the same documentation package from your internal appeal
• The IRO will contact your insurer and your doctors directly if needed

The external review decision is typically binding on the insurer.

Step 7: Additional Escalation Paths

If external review doesn't resolve your case, you have further options:

State Insurance Commissioner complaint: Your state regulates insurance companies. A formal complaint puts the insurer on notice and can result in an investigation. Many states have patient assistance programs that intervene on your behalf.

State insurance ombudsman: A free, independent resource in many states to help consumers navigate insurance disputes.

Attorney: For high-value denials or patterns of insurer misconduct, an attorney specializing in insurance bad faith may take your case on contingency.

Federal complaint: For ERISA plan violations, you can file with the Department of Labor's Employee Benefits Security Administration.

The Key to Success: Start Early, Be Thorough, Miss Nothing

The patients who win appeals are the ones who document everything, submit complete packages, and meet every deadline. It takes effort — but the win rate for well-prepared appeals is remarkably high.

Fight Back With ClaimBack

ClaimBack guides you through every step of this process — from organizing your documentation to crafting a compelling appeal letter. We make the confusing process clear.

Start your appeal at https://claimback.app/appeal

You have rights. Use them.

Related Reading

• How to Write an Insurance Appeal Letter
• Internal vs. External Insurance Appeal: Which Should You File?
• How to Request an External Review of an Insurance Denial