How to Appeal a Health Insurance Claim Denial: Step-by-Step

Receiving a denial letter from your health insurance company is stressful, especially when you expected a treatment, procedure, or prescription to be covered. But a denial is not the final word. Federal law gives you the right to challenge the decision, and the data shows that many denials are overturned when patients take the time to appeal.

Despite having a legal right to appeal, studies estimate that fewer than one in 500 denied claims are actually appealed. Meanwhile, external reviews overturn insurer denials more than 50% of the time. This guide explains the most common reasons health insurance claims are denied, walks you through the internal appeal and external review processes step by step, and provides practical advice for writing an effective appeal letter and meeting critical deadlines.

Common Reasons Health Insurance Claims Are Denied

Understanding the reason behind your denial is the essential first step toward a successful appeal. Your Explanation of Benefits (EOB) or denial letter will include a reason code or explanation. Here are the most common reasons health insurance claims are denied:

• Service not covered: The treatment, procedure, or medication may not be included in your plan's list of covered services. Some plans exclude specific treatments, experimental therapies, or elective procedures.
• Prior authorization not obtained: Many health plans require prior authorization (pre-approval) before certain procedures, specialist visits, or prescription drugs. If your doctor did not obtain prior authorization before providing the service, the insurer may deny the claim.
• Out-of-network provider: If you received care from a provider outside your plan's network, the claim may be denied entirely or covered at a significantly lower rate. This is especially common with HMO plans that require in-network referrals.
• Medical necessity dispute: The insurer may determine that the treatment was not medically necessary based on its clinical guidelines. This is one of the most common and most successfully appealed denial reasons.
• Billing or coding errors: Incorrect CPT codes, mismatched diagnosis codes, or data entry mistakes on the claim form can trigger automatic denials. These are often the simplest to fix.
• Duplicate claim: The insurer may flag a claim as a duplicate if it appears to match a previously submitted claim for the same service on the same date.
• Timely filing exceeded: Providers typically must submit claims within a certain time frame, often 90 to 180 days after the service. If the claim was submitted late, the insurer may deny it.
• Coordination of benefits issue: If you have coverage under more than one plan, the insurer may deny the claim pending clarification of which plan is primary.

Many denials related to out-of-network care involve misunderstandings about how network restrictions work. For a detailed explanation of provider networks, read our guide on in-network vs. out-of-network coverage.

Step 1: Review Your Denial Notice Carefully

When you receive a denial, start by reading the denial letter or EOB thoroughly. Your insurer is required by law to provide you with a clear explanation of why the claim was denied. Look for the following details:

• The specific reason or reason code for the denial
• The clinical or contractual basis for the decision
• The deadline and instructions for filing an appeal
• Your right to request the insurer's internal guidelines or criteria used to make the decision
• Contact information for further questions

If the denial is unclear, call the member services number on your insurance card and ask a representative to explain the decision in detail. Take careful notes during the call, including the date, time, and the name of the person you spoke with. Request a written copy of the specific plan provision or clinical guideline that was used to deny your claim.

Step 2: Understand Your ACA Appeal Rights

The Affordable Care Act significantly strengthened consumer protections when it comes to claim denials. Under the ACA, all non-grandfathered health plans must provide a two-step appeals process: first an internal appeal, then an external review. These protections apply to most individual, family, and employer-sponsored health plans.

Key ACA appeal protections include:

• 180-day window: You have at least 180 days from the date of the denial to file an internal appeal.
• New evidence allowed: You have the right to submit new evidence and documentation as part of your appeal, even if it was not included in the original claim.
• Independent reviewer: The internal appeal must be reviewed by someone who was not involved in the original denial decision.
• Expedited process: For urgent medical situations, you can request an expedited internal appeal and receive a decision within 72 hours.
• External review guarantee: If the internal appeal is denied, you have the right to an external review by an independent third party.

These protections apply whether you purchased your plan through the ACA marketplace or through your employer. To learn more about marketplace coverage and your rights, see our guide on ACA marketplace health insurance.

Step 3: Gather Supporting Documentation

A well-documented appeal is far more likely to succeed. Before you submit anything, take the time to assemble comprehensive supporting evidence. Your goal is to demonstrate that the denied service was medically necessary, properly coded, and covered under your plan's terms.

Documentation to gather includes:

• Letter of medical necessity from your doctor: This is the single most important document in most appeals. Your physician should explain your diagnosis, why the treatment was necessary, what alternatives were considered, and why the denied service was the most appropriate option.
• Medical records and clinical notes: Include relevant office visit notes, lab results, imaging studies, pathology reports, and any other records that document your condition and the need for treatment.
• Peer-reviewed medical literature: Published studies or clinical guidelines from medical organizations that support the treatment can strengthen your case, especially for medical necessity disputes.
• Your plan documents: Review your Summary of Benefits and Coverage (SBC) and the full plan document. Identify the specific language that supports coverage for the denied service.
• Prior treatment history: Records showing previous treatments you tried that were unsuccessful can support the medical necessity of the denied treatment.

Step 4: Write an Effective Appeal Letter

Your appeal letter is the foundation of your case. A clear, well-organized letter that directly addresses the reason for the denial will be far more effective than a vague or emotional one. Here is what to include in your appeal letter:

1. Your identifying information: Include your full name, date of birth, policy number, group number if applicable, and the claim number from the denial notice.
2. A clear statement of purpose: State that you are filing a formal appeal of the denial, and reference the date of the denial letter and the specific service that was denied.
3. Your argument against the denial: Address the specific denial reason directly. If the insurer said the service was not medically necessary, explain why it was. If it was a coding error, identify the correct code. Reference your plan language and attach supporting evidence.
4. A list of enclosed documents: Itemize every document you are including with the appeal, such as your doctor's letter of medical necessity, medical records, and relevant plan language.
5. A request for a specific outcome: Clearly state what you want, whether that is full coverage of the denied claim, reconsideration at in-network rates, or authorization for a pending treatment.

Keep the tone professional and factual. Avoid emotional language and focus on the medical and contractual facts. A one- to two-page letter is usually sufficient for the written portion; let the supporting documents carry the detailed clinical evidence.

Step 5: File the Internal Appeal

The internal appeal is your first formal step in challenging a denial. You are asking your insurance company to have a new reviewer, one who was not involved in the original decision, reexamine your claim along with any new evidence you provide.

Key points about the internal appeal process:

• Deadline: You typically have 180 days from the date of the denial to file your internal appeal under ACA-compliant plans. Do not wait until the last minute.
• Submission method: Submit your appeal via certified mail with a return receipt, or through any electronic submission method your insurer offers. Keep proof that the appeal was received.
• Response timeline: For non-urgent claims, your insurer must respond within 30 days for pre-service denials and 60 days for post-service denials. For urgent care, the response must come within 72 hours.
• Keep copies: Make copies of everything you submit. You may need this documentation later for an external review or a complaint to your state insurance commissioner.

Your doctor or their office staff can submit the internal appeal on your behalf if you provide written authorization. Many physician practices have staff experienced in handling insurance appeals, and their involvement can be a significant advantage.

Step 6: Request an External Review

If your internal appeal is denied, the next step is to request an external review. This is where an independent third party, someone with no connection to your insurance company, reviews all the evidence and makes a decision. Under the ACA, the external reviewer's decision is binding on the insurer. If they rule in your favor, your insurance company must cover the claim.

Important facts about external review:

• Deadline: You generally have four months from the date of the internal appeal denial to request an external review.
• Decision timeline: The external reviewer typically issues a decision within 45 days. For urgent cases, an expedited external review decision must be made within 72 hours.
• Success rates: External reviews are highly favorable for consumers. Data from multiple state insurance departments shows that more than 50% of external reviews result in the insurer's denial being overturned. This makes external review one of the most powerful tools available to you.
• No cost to you: Under the ACA, external reviews are conducted at no cost to the consumer. You do not have to pay for the review.

In certain situations, you may be able to bypass the internal appeal and go directly to an external review. This includes cases where the insurer failed to follow proper procedures, when waiting for an internal appeal could jeopardize your life or health, or when the denial involves an urgent admission, availability of care, or a continued stay in a facility.

Appealing Prior Authorization Denials

Prior authorization denials occur before you receive a service. Your insurer has reviewed a request and determined that it will not approve coverage for the proposed treatment, procedure, or medication. These denials follow the same appeal process as post-service denials, but timing is especially critical because delaying treatment can affect your health.

If your doctor determines that waiting for a standard appeal timeline could seriously jeopardize your health, you can request an expedited appeal. Under ACA rules, your insurer must issue a decision on an expedited internal appeal within 72 hours. If the expedited internal appeal is denied, you can immediately request an expedited external review, which must also be decided within 72 hours.

For prior authorization denials, your doctor's involvement is essential. They can provide the clinical justification for why the requested service is necessary and help expedite the process. Ask your physician to call the insurer's medical director to discuss the case, as peer-to-peer reviews can sometimes resolve prior authorization disputes quickly.

Appealing Emergency Room Claim Denials

Emergency room claim denials have become increasingly common in recent years, with some insurers using automated systems to retroactively deny ER claims based on the final diagnosis rather than the presenting symptoms. Under the ACA, health plans are required to cover emergency services without prior authorization and regardless of whether the ER is in or out of network.

The ACA applies a prudent layperson standard, which means that coverage should be based on your symptoms at the time you sought emergency care, not on the final diagnosis. If a reasonable person in the same situation would have believed they were experiencing a medical emergency, the claim should be covered. If your ER claim is denied retroactively, include a detailed description of your symptoms at the time, the ER physician's notes, and any documentation of the severity of your condition in your appeal.

Getting Your Doctor's Support

Your doctor is your most important ally in the appeals process. Their medical expertise and documentation can make the difference between a successful and unsuccessful appeal. Here is how to enlist their support effectively:

• Request a letter of medical necessity: Ask your doctor to write a detailed letter explaining your diagnosis, why the denied treatment was medically necessary, what alternative treatments were considered and why they were insufficient, and what the consequences of not receiving the treatment would be.
• Ask about a peer-to-peer review: Your doctor can request a peer-to-peer conversation with the insurer's medical director. This direct physician-to-physician discussion can sometimes resolve the denial without a formal appeal.
• Provide clinical evidence: Ask your doctor to include relevant clinical notes, test results, imaging studies, and references to peer-reviewed medical literature or clinical practice guidelines that support the treatment.
• Authorize your doctor to appeal on your behalf: You can sign an authorization form allowing your doctor's office to file the appeal directly. Many practices have dedicated staff for handling insurance disputes.

Understanding Key Deadlines

Missing a deadline can forfeit your right to appeal, so it is critical to track every date carefully. Here are the key timelines to know:

• Internal appeal: 180 days from the date of the denial notice for ACA-compliant plans. Some employer plans may have shorter windows, so check your denial letter.
• External review: Four months from the date of the internal appeal denial.
• Insurer response to internal appeal: 30 days for pre-service denials, 60 days for post-service denials, 72 hours for urgent cases.
• External review decision: 45 days for standard cases, 72 hours for urgent cases.

Mark these dates on your calendar as soon as you receive a denial. Understanding your plan's cost-sharing structure can also help you evaluate whether the denied amount is worth appealing. For more on how your plan's costs work, see our guide on copays, coinsurance, and deductibles.

Filing a Complaint with Your State Insurance Commissioner

If you believe your insurance company is not following the law, not adhering to your plan's terms, or not handling your appeal properly, you can file a complaint with your state insurance commissioner. Every state has an insurance department that oversees insurance companies and investigates consumer complaints.

A state insurance commissioner complaint can be filed at any point in the process, even while your appeal is pending. Filing a complaint may:

• Prompt the insurer to take a closer look at your case
• Trigger an investigation into the insurer's denial practices
• Result in the insurer being required to follow state regulations
• Provide you with additional guidance on your rights and options

You can find your state insurance department through the National Association of Insurance Commissioners (NAIC) website at naic.org. Many states also have consumer assistance programs that offer free help with insurance disputes.

For employer-sponsored plans governed by ERISA, you also have the right to file a lawsuit in federal court after exhausting the plan's appeal process. Some patients consult with an attorney who specializes in healthcare or insurance law, particularly for high-value claims or systemic denial patterns.

Tips for a Successful Health Insurance Claim Appeal

Appeals backed by strong documentation and clear reasoning succeed at much higher rates. Here are practical strategies to maximize your chances:

• Act immediately: Begin the appeal process as soon as you receive the denial. Gathering medical records, obtaining a letter from your doctor, and preparing your appeal letter all take time.
• Address the denial reason directly: Do not write a general letter. Target the specific reason given for the denial and provide evidence that refutes it.
• Request the insurer's clinical criteria: You have the right to ask for the specific guidelines or medical policy the insurer used to deny your claim. Understanding their criteria helps you tailor your appeal.
• Check for coding errors: Ask your provider's billing department to verify that the correct CPT and ICD-10 codes were used. A simple coding mistake is one of the most common and easily correctable causes of denial.
• Document everything: Keep copies of all correspondence, forms, and documents. Record the date, time, and summary of every phone call with the insurance company.
• Do not give up after one denial: The appeals process exists specifically because initial denials are often incorrect. If your internal appeal fails, pursue the external review. The data shows that persistence pays off.

The Bottom Line

A health insurance claim denial does not have to be the final answer. Federal law, particularly the Affordable Care Act, guarantees your right to a fair appeal process, including both an internal appeal and an independent external review. The statistics are on your side: more than half of external reviews overturn insurer denials, yet the vast majority of consumers never exercise their appeal rights.

Start by understanding why your claim was denied. Gather strong supporting documentation, including a letter of medical necessity from your doctor. Write a clear, factual appeal letter that directly addresses the denial reason. File your internal appeal promptly and, if necessary, follow through with an external review. If you encounter obstacles, your state insurance commissioner is an additional resource.

Understanding your health insurance plan thoroughly before you need care can also help prevent denials in the first place. Knowing your plan's network, prior authorization requirements, and covered services reduces the risk of surprises. For guidance on selecting the right plan for your needs, see our article on how to choose health insurance.

This article is for educational purposes and does not constitute legal or medical advice. Appeal timelines, rights, and procedures vary by plan type, state, and individual circumstances. Contact your insurance company, your state insurance department, or a consumer assistance program for guidance specific to your situation.