How to Write an Insurance Appeal Letter That Actually Works

You've been denied. Now you need to appeal. But your letter is your first chance to convince the insurer (or an independent reviewer) to overturn their decision.

This guide shows you exactly how to write an insurance appeal letter that works. The structure, tone, and evidence matter. Most people write emotional, rambling letters. You're going to write a professional, evidence-backed letter that insurers take seriously.

Here's the formula.

The Golden Rule: Be Professional, Not Emotional

Your appeal letter will be read by someone who makes dozens of claim decisions daily. They're not moved by emotion. They're moved by evidence.

This works: "According to NCCN clinical guidelines (version 2025), this treatment is recommended for patients with my diagnosis. The treatment has established efficacy supported by published clinical trials. I respectfully request reconsideration."

This doesn't: "I'm desperate and this treatment could save my life. How could you deny someone in my situation? This is cruel and unfair."

The first letter sounds credible. The second sounds like you're desperate (even if you are). Credibility wins.

Your tone should be:

• Professional and formal
• Respectful but firm
• Fact-based
• Evidence-backed
• Not accusatory or emotional

The Structure That Works

Follow this structure exactly:

Section 1: Introduction (2-3 sentences)

State clearly what you're doing.

Example: "I am writing to formally appeal the denial of my insurance claim for [specific treatment/procedure] dated [date]. Claim number: [claim number]. I believe this denial was incorrect and request full reconsideration of my case."

Keep it brief. Don't explain the whole story yet.

Section 2: The Specific Denial (1-2 sentences)

State exactly what the insurer said.

Example: "Your letter dated [date] stated that my claim was denied because the treatment was 'not medically necessary.' I respectfully disagree with this determination."

Quote the insurer's language if possible. This shows you read their letter carefully.

Section 3: Why the Denial Is Wrong (3-5 paragraphs)

This is your main argument. Address the insurer's specific reason for denial.

For "Not Medically Necessary" denials:

• Cite clinical guidelines supporting the treatment
• Reference your treating doctor's medical judgment
• Explain why the treatment is necessary for your specific condition
• Provide evidence of standard medical practice

For "Pre-Existing Condition" denials:

• Provide medical records showing when the condition began
• Show proof of disclosure (if you disclosed it)
• Explain why the exclusion is unfair or inapplicable

For "Prior Authorization" denials:

• Explain why you need the treatment now
• Cite medical guidelines
• Show that prior auth should have been granted

For "Out-of-Network" denials:

• Show emergency care exception applies, or
• Show continuity of care exception, or
• Show no adequate in-network options exist

Structure each argument as:

1. Statement of the issue
2. Evidence supporting your position
3. Why the insurer's reasoning is flawed
4. Respectful request for reversal

Example format: "The insurer stated that the treatment is 'not medically necessary.' However, this determination appears to be based on incomplete medical information. According to [clinical guideline], this treatment is recommended for patients with [your diagnosis]. Additionally, my treating physician [doctor's name] has provided a detailed clinical justification explaining why this treatment is necessary for my specific case (attached). The insurer's determination appears to contradict established clinical guidelines and my physician's professional judgment."

Section 4: Supporting Evidence (1-2 sentences)

List what you're attaching.

Example: "I have attached the following supporting documentation: (1) letter from my treating physician dated [date], (2) clinical guidelines from [source] supporting this treatment, (3) my complete medical records, (4) [other evidence]."

Section 5: Request for Reconsideration (1-2 sentences)

Be specific about what you want.

Example: "I respectfully request that you reconsider and approve my claim in full. I am available for a peer-to-peer review between my physician and your medical director if that would be helpful. Please respond within 30 days of receipt of this letter."

Section 6: Closing

"Sincerely, [Your name] [Your policy number] [Your claim number] [Your contact information] Date"

Keep it simple. No fancy closing.

Evidence Organization

Don't just list evidence. Organize it clearly so the reviewer can find what they need.

Create an attachment index: "Attached documentation:

1. Attachment A: Letter from Dr. [name] dated [date] explaining clinical medical necessity
2. Attachment B: [Guideline name] clinical guidelines, pages [X-Y]
3. Attachment C: My medical records from [date] to [date]
4. Attachment D: [Other relevant documents]"

Then actually number/label each attachment so the reviewer can reference it easily.

Use highlighting strategically:

• In guideline passages, highlight the specific sentence supporting your case
• In medical records, highlight diagnostic information
• In doctor's letter, highlight the key recommendation

Don't highlight everything—that defeats the purpose. Highlight only the most important points.

Key Elements That Win Appeals

1. Your Doctor's Letter (Most Important)

This carries more weight than anything else. Your doctor must write a detailed letter that:

• States the condition and diagnosis
• Explains the treatment's medical necessity
• Cites clinical reasons (not just "I think it's necessary")
• Addresses the insurer's specific objection
• Uses professional medical language

Bad doctor's letter: "I recommend treating this patient. Please approve the claim."

Good doctor's letter: "[Patient name] has been diagnosed with [condition]. This condition is characterized by [specific clinical findings]. The recommended treatment by the [specialty field] is [specific treatment]. In this patient's case, this treatment is medically necessary because [specific clinical reasons]. This approach aligns with current clinical guidelines from [guideline name]. Without this treatment, the patient faces [specific medical risk]. I strongly support approval of this claim."

If your doctor's letter is weak, ask them to rewrite it more thoroughly.

2. Clinical Guidelines

Clinical guidelines show that your treatment is standard of care. This is powerful.

Examples of credible guidelines:

• NCCN (National Comprehensive Cancer Network)
• ASCO (American Society of Clinical Oncology)
• ACC (American College of Cardiology)
• AHA (American Heart Association)
• Specialty society guidelines
• Government health authority guidelines

Print the relevant passage. Highlight the section supporting your treatment. Reference it by name and version.

Example in your letter: "According to NCCN Clinical Practice Guidelines for [condition] (version 2025), [treatment] is recommended for patients with [your diagnosis]."

Then attach the guideline passage.

3. Complete Medical Records

Incomplete medical records often cause denials. Complete records often reverse them.

Gather:

• All doctors' notes
• All test results
• All imaging
• Hospital records (if applicable)
• Any specialist evaluations
• Treatment history

The insurer's reviewer might not have these. You provide them. Often the complete picture supports approval.

4. What NOT to Include

Don't include:

• Emotional language ("My family is suffering")
• Personal story ("I've been sick for years")
• Attacks on the insurer ("Your company is greedy")
• Irrelevant information
• Lawyer language or legal arguments (unless you have legal advice)

These weaken your appeal. Stick to medical and policy facts.

The Tone: Firm But Respectful

Your letter should convey:

• You've carefully reviewed the decision
• You respectfully disagree
• You have evidence supporting your position
• You expect reconsideration

This tone: "I respectfully request reconsideration. The treatment is supported by [evidence]. The denial appears inconsistent with [standard/guideline]. I believe approval is warranted."

Not this tone: "Your denial was wrong. You clearly made a mistake. I demand immediate approval."

The first sounds credible. The second sounds like you're upset (even if justified).

Special Handling: The Peer-to-Peer Request

Many medical appeals are resolved through peer-to-peer review—your doctor talking to the insurer's doctor.

Include this in your letter: "I request a peer-to-peer review between my treating physician [full name, credentials, phone number] and your medical director. My physician is available [specific times/dates]. This conversation should allow the medical director to understand the clinical basis for the treatment recommendation directly."

This is often enough to flip the decision because your doctor can explain clinical reasoning verbally.

Addressing Specific Denial Reasons

For "Not Medically Necessary"

"The insurer determined the treatment was 'not medically necessary.' However, [doctor's medical reasoning]. Additionally, this treatment is recommended in [guideline name] for patients with my diagnosis. The determination appears inconsistent with established clinical standards."

For "Pre-Existing Condition"

"The insurer cited a pre-existing condition exclusion. However, [explain why it doesn't apply]. The condition began after my policy started, as evidenced by [medical records]. Additionally, I disclosed [relevant information] at point of sale."

For "Waiting Period"

"The insurer cited an unmet waiting period. However, [explain why not applicable]. My treatment needs are urgent due to [medical reason]. I request waiver of the waiting period."

For "Prior Authorization"

"Prior authorization was denied. However, [address the reason given]. The treatment is medically necessary and supported by [guideline]. I request that authorization be granted."

For "Out-of-Network"

"The claim was denied for out-of-network status. However, this situation qualifies for [emergency care/continuity of care/no adequate provider] exception. Under [policy/regulation], I'm entitled to in-network benefits."

Length: How Long Should It Be?

1-2 pages. That's it.

The insurer's reviewer will spend maybe 10-15 minutes on your appeal. Make every sentence count. No rambling. No background story longer than one paragraph.

If you need more space for evidence, use attachments. The letter itself should be concise.

Format

Keep it simple:

• Standard letter format
• Plain font (Arial, Times New Roman)
• Single-spaced, 1-inch margins
• Your name and contact info at top
• Date
• Insurer's address
• Professional salutation ("Dear [Claims Manager]:")
• Body paragraphs
• Professional closing

Don't make it fancy. Fancy looks like you're trying too hard. Plain and professional wins.

How to Submit

Submit multiple ways:

1. Registered mail with signature confirmation
2. Email with read receipt requested
3. Online portal (if available)
4. Fax with cover page showing confirmation

Keep proof of submission. You'll need it if the insurer claims they never received it.

When to Use ClaimBack

Writing a compelling appeal is hard. You're stressed, you're confused about medical terminology, you're worried about your health.

ClaimBack can analyse your case and write your appeal letter in minutes — Start Free →

You provide:

• Your denial letter
• Your policy document
• Your medical records
• Your doctor's notes

ClaimBack analyzes everything and generates a professional appeal letter addressing your specific situation. You review it (you don't have to accept it as-is), make any changes you want, then send it.

This takes the stress and guesswork out of appeal writing. The letter comes back professional, evidence-backed, and targeted to your specific denial reason.

Final Checklist Before Sending

• Letter is professional and fact-based (no emotion)
• I've addressed the insurer's specific denial reason point-by-point
• I've included supporting evidence (doctor's letter, guidelines, medical records)
• I've requested peer-to-peer review (if applicable)
• I've clearly stated what I want (claim approval)
• Letter is 1-2 pages maximum
• Formatting is professional and clean
• I have proof of how I'm submitting it
• I've kept a copy for my records
• I know the insurer's response deadline

Your appeal letter is your voice when you can't speak directly to the decision-maker. Make it count.

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Disclaimer: ClaimBack provides AI-generated appeal assistance for informational purposes only. ClaimBack is not a law firm and does not provide legal advice. Always review your appeal letter before sending and consider professional advice for complex or high-value claims. Regulatory processes vary — always verify current procedures with your insurer or regulator.

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Ready to fight your denial? ClaimBack analyses your case and writes a professional appeal letter in minutes — Start Free →