Guides · Last reviewed October 14, 2026

How to appeal a health insurance denial

You generally have 180 days from the denial notice to file an internal appeal with private and Marketplace plans. If the insurer says no again, you can ask for an independent external review within 4 months, and the insurer must accept that decision.

Why it's worth appealing

ACA Marketplace insurers denied about 19% of in-network claims in 2024, but patients appealed fewer than 1% of those denials. Of the internal appeals filed, insurers reversed roughly one in three.

Step 1: Read the denial notice

Find the claim number, the exact reason for the denial, and the deadline. Common reasons: "not medically necessary," "out of network," "no prior authorization," "experimental," or a coding error by the provider.

Step 2: Ask for the claim file

You can request, free of charge, the documents used to decide your claim, including the specific plan rule or clinical guideline. Knowing the exact criteria lets you answer them point by point.

Step 3: Get a letter from your doctor

A letter of medical necessity from the treating provider is often the strongest evidence. It should explain your diagnosis, what was tried before, and why this care was needed.

Step 4: File the internal appeal

• Send a written appeal letter with the claim number, member ID, the denial reason, and why it's wrong.
• Attach the denial notice, your doctor's letter, and relevant records.
• Keep copies and send it in a way you can track.

Insurers generally must decide within 30 days for care you haven't received yet and 60 days for care you already got. If waiting could seriously harm your health, ask for an expedited appeal.

Step 5: Request an external review if needed

If the internal appeal is denied, file a written external review request within 4 months of the final denial. An independent reviewer decides, usually within 45 days, or within 72 hours for urgent cases. Under the federal process there's no charge; other processes may charge up to $25.

Employer plans, Medicare and Medicaid

Most job-based plans follow similar steps. Medicare and Medicaid have their own processes: see our Medicare appeal guide, and for Medicaid follow the deadline on your notice.

Guides for specific insurers

• Appealing a UnitedHealthcare denial
• Appealing an Aetna denial
• Appealing a Cigna denial
• Appealing a Blue Cross Blue Shield denial
• Appealing an Anthem denial
• Appealing a Kaiser Permanente denial
• Appealing a Humana (Medicare Advantage) denial

Common questions

Sources

• KFF: Claims denials and appeals in ACA Marketplace plans in 2024
• HealthCare.gov: Internal appeals
• HealthCare.gov: External review

Billmira is a self-help information tool, not a law firm, and this isn't legal or medical advice. Rules change and plans differ; check the official sources above and your own documents.