How to Appeal an Insurance Claim Denial (2026 Guide)

Your insurance company denied your claim. You got a letter full of codes and legal language, and it feels like a dead end. It isn't.

Internal appeals overturn insurance denials 40–60% of the time. External reviews — where an independent organization reviews the decision — succeed 50–65% of the time. The Affordable Care Act guarantees your right to both. And they're free.

The reason most people don't appeal isn't that their claims aren't valid. It's that the process feels opaque. This guide removes that excuse. By the end, you'll know exactly what to do, in what order, and by what deadline.

First: Understand Your Denial Letter

Before you appeal anything, you need to understand why you were denied. Federal law (the ACA) requires insurers to send a Notice of Adverse Benefit Determination (NOABD) — your denial letter — that includes:

• The specific reason the claim was denied
• The plan provision, exclusion, or clinical standard used
• Your right to appeal and the deadline to do so
• Instructions for requesting an external review
• Contact information for your state's consumer assistance program

If your denial letter is missing any of these elements, note it. An insurer that fails to provide proper notice has potentially violated ACA regulations — which is useful ammunition in your appeal.

Common denial reasons (and what they mean for your appeal)

The denial code tells you what kind of fight you're in:

• Medical necessity: The insurer says the service wasn't necessary for your condition. This is the most common type — and the most often reversed when your doctor provides supporting documentation.
• Prior authorization not obtained: A required pre-approval was missing. Check whether your provider was supposed to get it. If the error was theirs, the appeal process is often handled provider-to-insurer without you.
• Out-of-network: You saw a provider outside your plan's network. The No Surprises Act (effective 2022) protects you from surprise bills for emergency care and some non-emergency situations at in-network facilities — worth citing if applicable.
• Experimental or investigational: The insurer considers the treatment unproven. Appeals based on peer-reviewed evidence and your doctor's clinical rationale are effective here.
• Benefit limit: You hit your plan's cap. Review your plan documents carefully — limits are sometimes miscalculated, and mental health parity laws (the MHPAEA) prohibit stricter limits on mental health benefits than on comparable medical benefits.
• Coding error: The wrong CPT or ICD-10 code was used on the claim. This is often fixed at the billing office level without a formal appeal — call your provider's billing department first.

Step 1: Request Your File

You have the right to request a complete copy of your claim file — all documents, guidelines, and criteria the insurer used to make its decision. Call the member services number on your denial letter and ask for your "complete claims file" under the ACA's claims and appeals regulations. This is free.

Why this matters: You can't argue against criteria you haven't seen. Your appeal needs to specifically address the standard the insurer applied. If they used a clinical policy bulletin, you need that bulletin before you write a word of your appeal letter.

Step 2: Know Your Deadline

Federal law requires insurers to allow at least 180 days from the date you receive your denial notice to file an internal appeal. Most major insurers match this minimum:

Insurer	Internal Appeal Deadline	Expedited (Urgent)	External Review
Aetna	180 days	72 hours	4 months post-final denial
Blue Cross Blue Shield	180 days	72 hours	4 months post-final denial
Cigna	180 days	72 hours	4 months post-final denial
UnitedHealthcare	180 days	72 hours	4 months post-final denial
Humana	60–180 days	72 hours	4 months post-final denial

Always verify your specific deadline on your denial letter — employer-sponsored and self-insured plans can have different timelines.

Step 3: Internal Appeal — The First Line

An internal appeal asks the insurance company to reconsider its own decision — but federal law requires a different staff member to conduct the review (not the person who denied you originally).

What makes an effective appeal letter

Most appeal letters fail because they're emotional, not clinical. Insurers respond to three things: plan language, clinical evidence, and regulatory obligations. Your letter should address all three.

Get your doctor involved

Ask your physician to write a letter of medical necessity. It should state: the diagnosis, why the specific treatment was the appropriate standard of care, why alternatives would be inadequate, and cite relevant clinical guidelines. A doctor's letter almost always strengthens an appeal — and for medical necessity denials, it's close to mandatory.

If the denial is for medical necessity, also ask your doctor about requesting a peer-to-peer review — a direct phone call between your physician and the insurer's medical director. Peer-to-peer reviews resolve many denials before a formal appeal is even decided. They cost nothing and take 20 minutes.

How to submit

Submit via certified mail (return receipt) or the insurer's member portal with a confirmed submission timestamp. Keep everything — a copy of your letter, all attachments, the tracking number. Insurers have lost appeal submissions before, and your documentation is the only proof you filed on time.

What happens next

Insurers must decide internal appeals within:

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

If the insurer doesn't respond within these windows, you can proceed directly to external review as if the internal appeal was denied.

Step 4: External Review — The Independent Arbiter

If your internal appeal is denied — or if the insurer doesn't respond in time — you can request an external review. This sends your case to an Independent Medical Organization (IMO) or Independent Review Organization (IRO) that has no financial relationship with your insurer.

The insurer must accept the external reviewer's decision. This is federal law under the ACA. If the reviewer overturns the denial, the claim gets paid — full stop.

What qualifies for external review

Federal rules allow external review for any denial based on medical necessity, appropriateness, health care setting, level of care, or effectiveness. Some states have broader protections that extend external review rights further.

Rescissions — cancellations of coverage — also qualify for external review.

How to request external review

Your final denial notice must include instructions for requesting external review. You typically have 4 months from the date of the final denial notice to file. The process:

1. Submit a request to your insurer using their external review form (or in writing to the address on the denial letter)
2. The insurer forwards your file to an accredited IRO, typically within 5 business days
3. The IRO reviews and issues a final decision within 45 days (4 business days for urgent)

The fee is capped at $25 by federal regulations. It's waived if you win.

Step 5: State Resources and Last Resorts

If external review upholds the denial, you haven't necessarily run out of options — but the remaining paths are harder:

State Insurance Commissioner

Every state has an insurance commissioner's office that handles consumer complaints. File a complaint if the insurer violated state law, failed to follow proper procedures, or if you believe the denial was handled in bad faith. Commissioners can investigate insurers and order them to reconsider claims. Find your state commissioner at NAIC.org.

No Surprises Act protections

If your denial involves a surprise bill from an out-of-network provider in an emergency situation or at an in-network facility, the No Surprises Act may apply. File a complaint at the federal No Surprises Help Desk (1-800-985-3059) or online at CMS.gov/nosurprises.

Employee Benefits Security Administration (ERISA plans)

If you have employer-sponsored insurance, your plan is likely governed by ERISA. The Department of Labor's Employee Benefits Security Administration handles ERISA complaints. An ERISA violation by your plan can result in mandatory coverage plus attorney's fees.

Patient advocates and attorneys

Non-profit patient advocacy organizations can help navigate the process for free. For large claims (especially denied cancer treatments or surgeries), a patient advocate attorney who works on contingency may be worth consulting — they get paid only if you win.

Denied for Medical Necessity? These Numbers Matter

Insurance companies don't like publishing their appeal overturn rates, but ACA regulations require reporting. What the data shows:

• 40–60% of internal appeals succeed — across most major insurers
• 50–65% of external reviews succeed — when claims reach independent review
• Technical/administrative denials (missing auth, coding errors) overturn at rates closer to 78% once properly documented
• Home health and SNF denials reverse at similar rates when continuity of care is documented
• Peer-to-peer reviews resolve a significant portion of medical necessity denials before formal appeal is even decided

These numbers aren't a guarantee. But they're evidence that filing an appeal isn't a long shot — it's a process that works when executed correctly.