How to Appeal a Denied Health Insurance Claim: Step-by-Step Guide

Getting a letter that says your health insurance claim has been denied is one of the most frustrating experiences in the American healthcare system. You did everything right — went to the doctor, got treatment, filed the paperwork — and your insurer says no.

Here's what most people don't know: you have the legal right to appeal every denied claim, and when people do appeal, they win far more often than you'd expect. External reviews overturn insurance denials 40–60% of the time. The odds are actually in your favor — if you show up.

This guide walks you through the entire appeal process, step by step, in plain English. No legal background required.

Why Do Health Insurance Claims Get Denied?

Before you appeal, it helps to understand why your claim was denied. The denial letter is required by law to give you the reason. Here are the four most common denial reasons and what they actually mean:

1. "Not Medically Necessary"

This is the most common denial reason. It means your insurance company's reviewer disagrees with your doctor about whether you needed the treatment. This is almost always worth appealing — your doctor knows your situation better than a reviewer who's never met you.

2. "Out of Network"

The provider who treated you isn't in your plan's network. But check this carefully: if you received emergency care, or if you were treated at an in-network facility by an out-of-network provider you didn't choose, the No Surprises Act may protect you from this charge entirely.

3. "Not a Covered Benefit"

Your insurer says this service isn't covered under your plan. Request the specific policy language they're citing. Sometimes they're wrong, or they're applying the wrong exclusion to your situation.

4. "Prior Authorization Not Obtained"

Your insurer required pre-approval for this treatment and it wasn't obtained. This may be your provider's error, not yours. If your doctor's office failed to get prior auth, they may be responsible for resubmitting — not you.

Your Legal Right to Appeal

Under the Affordable Care Act (ACA), every person with health insurance has the legal right to:

1. An internal appeal — Your insurer must review the denial again, using a different reviewer than the one who denied it initially.
2. An external review — If the internal appeal is denied, you can request an independent third party review the decision. This reviewer has no relationship with your insurance company.

These are federal rights. Your insurance company cannot opt out. They are required by law to tell you how to exercise these rights in your denial letter.

According to a KFF survey, 60% of insured Americans don't know they have these rights. And 86% don't know what government agency to contact for help. The insurance industry is counting on you not knowing this.

Step 1: Read Your Denial Letter Carefully

Your denial letter (or Explanation of Benefits) contains critical information you'll need for your appeal. Look for these four things and write them down:

• The specific reason for denial — the exact language and any codes cited
• Your deadline to appeal — typically 180 days for internal appeals, but check your letter. Missing this deadline means losing your right to appeal.
• How to file your appeal — the letter must include instructions
• The reference or claim number — you'll need this for every phone call and piece of correspondence

Step 2: Call Your Insurance Company

Before you write anything, make one phone call. Call the number on your denial letter or the back of your insurance card, and say this:

"I'm calling about a denied claim. My reference number is [X]. Can you tell me the specific clinical criteria you used to deny this claim?"

Write down everything they say. Word for word. Get the name of the person you spoke with, the date, the time, and a new reference number for this call.

This phone call does two critical things:

1. It tells you exactly what evidence you need to provide in your appeal. If they denied it as "not medically necessary," you now know which clinical guidelines they used, and your doctor can respond to those specific criteria.
2. It signals to the insurer that you're not going away. Most people accept the denial and never push back. The moment you ask for clinical criteria, you're flagged as someone who knows how to navigate the system.

Step 3: File Your Internal Appeal

Every insurer must provide a process for filing an internal appeal. The denial letter explains how. Here's what to include:

• Your name, member ID, and the claim number from the denial letter
• A clear statement that you are appealing the denial
• The specific reason they gave for the denial and why it's wrong
• A letter from your doctor explaining why the treatment was medically necessary. This is the single most powerful piece of evidence you can include. Ask your doctor to specifically address the clinical criteria the insurer cited.
• Any supporting documentation — medical records, lab results, peer-reviewed studies that support the treatment

Pro tip: Ask your doctor to request a peer-to-peer review. This is a phone call between your doctor and the insurer's medical reviewer. Many denials get overturned during this call because the reviewer hears directly from the treating physician.

Your insurer must respond to your internal appeal within 30 days for pre-service claims (before you receive treatment) or 60 days for post-service claims (after treatment). For urgent situations, they must respond within 72 hours.

Step 4: Request an External Review

If your internal appeal is denied, don't stop. You have the right to an external review — an independent third party, with no connection to your insurance company, reviews your case.

This is where the odds shift dramatically in your favor. External reviews overturn insurance denials 40–60% of the time. The independent reviewer looks at the medical evidence on its merits, not through the lens of the insurer's financial interests.

How to request one:

• Your insurer's internal appeal denial letter must tell you how to request an external review
• You typically have 4 months to file
• The review is free to you — the insurer pays for it
• The external reviewer's decision is binding on the insurance company

Step 5: File a Complaint With Your State

If you've exhausted your appeals, or if you believe your insurer isn't following the law, file a complaint with your state's Department of Insurance. This is free, and they are legally required to investigate.

Every state has a consumer complaint process. Search for "[your state] department of insurance complaint" to find the online form. Include:

• Your policy information
• The denial letter and claim number
• A summary of what happened and what you've done so far
• Copies of your appeal correspondence (keep originals for your records)

State regulators take these complaints seriously — they can compel insurers to reverse decisions, and patterns of complaints trigger formal investigations.

Key Laws That Protect You

• Affordable Care Act (ACA) — Guarantees your right to internal appeal and external review for all marketplace and employer-sponsored plans
• No Surprises Act — Protects you from surprise out-of-network bills in emergencies and at in-network facilities
• Mental Health Parity Act — Requires that mental health and substance use benefits are covered at the same level as medical/surgical benefits. If your behavioral health claim was denied, this law may be your strongest argument.

How Long Does the Appeal Process Take?

• Internal appeal: 30 days (pre-service) or 60 days (post-service). 72 hours for urgent cases.
• External review: Typically 45 days after you file.
• State complaint: Varies by state, but most acknowledge receipt within 2 weeks and investigate within 30–90 days.

The entire process from initial denial to external review resolution typically takes 2–4 months. It's not fast, but the alternative — paying a bill you don't owe — is worse.

When to Get Help

You can do this entire process yourself. But if your case is complex (high-dollar claims, experimental treatments, or repeated denials), consider:

• Your state's Consumer Assistance Program (CAP) — free help navigating insurance disputes, available in many states
• A patient advocate — organizations like the Patient Advocate Foundation offer free case management
• BenefitGuard — upload your denial letter and insurance documents, and get personalized guidance on your specific situation, including which laws protect you and what to say in your appeal

The Bottom Line

Insurance companies deny claims because the system is built on the assumption that you won't fight back. Only 0.1% of marketplace claims get formally appealed by patients — but when they do, the success rate is remarkably high.

You don't need a lawyer. You don't need to spend $200/hour on an advocate. You need to understand the process, know your rights, and follow through. This guide gives you everything you need to start.

One phone call. One appeal letter. That's all it takes to change the outcome.