Last updated: July 7, 2026
How to Write an Insurance Appeal Letter That Insurers Actually Respond To
Most insurance appeals fail — not because the patient is wrong, but because the letter doesn't speak the insurer's language. This guide shows you exactly what to include, what to cite, and how to structure your appeal for the best chance of success.
Why Most Insurance Appeals Get Denied Again
The number one reason appeals fail a second time: generic language without specific clinical guideline citations. Writing "my doctor says I need this procedure" is not enough. Insurers evaluate appeals against published clinical criteria sets, and if your letter doesn't reference those same criteria, it will likely be denied again.
According to KFF's analysis of ACA marketplace plans, the vast majority of denied claims are never appealed by consumers. Among those who do appeal, properly documented appeals that cite specific clinical guidelines see significantly higher overturn rates than generic appeals.
What Every Appeal Letter Must Include
1. Your Policy and Member Information
Include your full name, member ID, group number, date of birth, and the claim or reference number from your denial letter. Missing any of these can delay processing.
2. The Specific Denial Reason (Word for Word)
Quote the exact denial reason from your letter. Don't paraphrase — use the insurer's exact language and denial code. This shows you're responding to their specific determination, not making a general complaint.
3. Clinical Guideline Citations
This is where most appeals fail. You need to cite the specific clinical criteria your insurer uses to evaluate medical necessity. Common criteria sets include:
- MCG Guidelines (formerly Milliman) — used by many commercial insurers
- InterQual Criteria — used by UnitedHealthcare, Cigna, and others
- CMS National Coverage Determinations (NCDs) and Local Coverage Determinations (LCDs) — for Medicare/Medicaid claims
4. Supporting Documentation Checklist
- Letter of medical necessity from your treating physician
- Relevant medical records and test results
- Peer-reviewed studies supporting the treatment (if applicable)
- Documentation of prior treatments that failed (for step therapy denials)
5. A Clear Request With Your Appeal Deadline
Explicitly state what you're asking for (approval of the denied service or procedure) and note your appeal deadline. This creates a documented record and urgency.
How Long You Have to Appeal
Under the Affordable Care Act, you generally have 180 days (6 months) from the date you receive your denial to file an internal appeal.
For prior authorization denials specifically, the 2026 CMS Interoperability and Prior Authorization Final Rule requires health plans to respond to standard prior authorization requests within 7 calendar days and urgent requests within 72 hours.
For a complete breakdown of timelines by claim type, see our detailed appeal response timeline guide.
Sample Appeal Letter Structure
Note: This is a generic template structure, not a real appeal. Customize every section with your actual case details.
[Your Name]
[Your Address]
Member ID: [Your Member ID]
Group Number: [Your Group Number]
Claim Reference: [Claim/Reference Number]
Date: [Date]
[Insurance Company Appeals Department]
[Appeals Address from your denial letter]
RE: Appeal of Denial — [Procedure/Service Name]
Dear Appeals Review Committee,
I am writing to formally appeal the denial of [procedure/service] dated [denial date], reference number [number]. The stated reason for denial was: "[exact quote from denial letter]."
[Paragraph citing specific clinical guideline, e.g.: "Per MCG Guidelines, 28th Edition, Criterion [X.XX], this procedure meets medical necessity criteria when [specific conditions], all of which are documented in the enclosed medical records."]
[Paragraph from treating physician explaining clinical rationale]
I respectfully request that you reverse this denial and approve [procedure/service]. Please respond within the timeframe required under [applicable regulation].
Sincerely,
[Your Name]
The Hard Part: Finding the Right Clinical Guidelines
The difference between a generic appeal and one that gets overturned often comes down to a single thing: citing the exact clinical criteria your insurer uses. Writing "MCG Guidelines, 28th Edition, Criterion X.XX" is what changes outcomes — because it tells the reviewer you know exactly what standard they applied and why your case meets it.
The challenge is that these criteria sets are proprietary, complex, and constantly updated. Most patients don't even know which criteria set their insurer uses, let alone how to cite the specific criterion that applies to their case.
If your denial was for "not medically necessary", citing the right guideline is especially critical — it's the most common and most winnable denial reason when properly addressed.
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