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

by Michael Reynolds · January 25, 2026

Receiving a health insurance claim denial can feel like hitting a wall—confusing, stressful, and potentially expensive. But a denial is not always final: most denials can be challenged successfully with the right approach. This article breaks down why denials happen, how to read your Explanation of Benefits (EOB), the differences between internal and external appeals, step-by-step instructions for preparing and filing an appeal, sample language you can use, timelines to watch, and practical tips to avoid common pitfalls.

Understanding the Basics: What a Denial Means

A claim denial occurs when your insurer refuses to pay for some or all of the medical services billed by a provider or submitted by you. Denials can be full (the insurer refuses to cover the entire claim) or partial (the insurer covers some charges but not others). Denials may also show up as payment reductions, where the insurer pays less than the provider billed.

Important distinctions to understand early on:

Claim denial vs. claim rejection: A rejection often indicates missing or incorrect information in the claim submission. It’s usually fixed by resubmitting corrected information. A denial is a decision on the claim content itself.
Medical necessity vs. administrative reasons: Denials commonly cite medical necessity (insurer deems a service not medically necessary) or administrative reasons (pre-authorization not obtained, provider out-of-network, incorrect billing codes).
Pre-service vs. post-service denials: Pre-service denials happen before treatment (e.g., pre-authorization denied). Post-service denials occur after care has been delivered.

Step 1: Read Your Explanation of Benefits (EOB) Carefully

The Explanation of Benefits (EOB) is your first and most important document. It explains how your claim was processed, what your insurer paid, and what you may owe. An EOB is not a bill, but a related medical bill often arrives from the provider.

Key elements to locate on the EOB

Claim number and date of service
Provider name and billed amount
Amount allowed by the plan and amount paid
Patient responsibility (deductible, copay, coinsurance)
Denial or adjustment codes and short explanations
Contact information and appeal instructions

Tip: Make a copy (physical or digital) of the EOB and the provider bill. Highlight the denial reason and any claim codes. Those codes are often the key to understanding the insurer’s rationale.

Common Reasons Health Insurance Claims Get Denied

Denials stem from many causes—some trivial, others complicated. Common reasons include:

Administrative and paperwork errors: incorrect member ID, missing diagnosis code, incorrect billing codes (CPT, ICD-10), or wrong dates.
Lack of pre-authorization or prior authorization: many elective procedures, expensive tests, or specialist visits require prior approval.
Services considered not medically necessary: the insurer determines treatment isn’t supported by clinical guidelines or documentation.
Out-of-network provider: the provider is not in your insurer’s network or is in-network for a different plan type.
Duplicate claims or previously paid claims: the carrier thinks this charge was already paid.
Coordination of benefits issues: another insurer is primary for this service and should be billed first.
Coverage exclusions: cosmetic procedures, experimental treatments, or services excluded by the plan.
Missing or incomplete medical records: insufficient documentation to support the necessity of the service.

Step 2: Determine the Type of Appeal You Need

Most insurers offer multiple levels of appeal. Understanding these levels upfront helps you choose the right path and meet deadlines.

Internal (First-Level) Appeal

An internal appeal asks your insurer to review and reverse its decision. This is typically the first step and often required before moving to external review. Internal appeals are governed by the insurer’s internal procedures and timelines which will be listed in your policy materials and the denial letter.

External Review (Independent Review)

If an internal appeal is denied, you may qualify for an external review—an independent third-party review conducted by a state agency or independent review organization. External reviews are especially important for disputes over medical necessity. Federal law (for plans subject to ERISA and certain state laws) and state regulations determine when external review is available.

Administrative Appeals Under ERISA vs. Non-ERISA Plans

If your employer-sponsored plan is governed by ERISA (Employee Retirement Income Security Act), the federal law sets specific internal appeal requirements and sometimes limits legal actions until the internal appeal process is exhausted. Public programs like Medicare and Medicaid have their own appeal procedures.

Step 3: Track Deadlines and Timelines

Missing a deadline can forfeit your right to appeal. Key timelines vary widely:

Pre-service denials: insurers generally must respond quickly—often within 72 hours for urgent care, and within 15 days for non-urgent care.
Post-service denials: internal appeal windows often range from 30 to 180 days from the date of denial; state laws vary.
External review: you typically have a limited window after the final internal denial (often 60 days) to request external review.

Action: Immediately note appeal deadlines when you receive the denial and calendar reminders for internal and external deadlines.

Step 4: Gather Documentation — Build Your Appeal Packet

A strong appeal depends on documentation. Assemble the following:

The EOB and the insurer’s denial letter (include all pages)
Itemized bills from the provider
Your health insurance ID card (front and back copy)
Medical records and clinical notes supporting the necessity of the treatment (discharge summaries, lab results, imaging reports)
Prior authorization approval (if relevant) or documentation showing prior approval was requested
Letters from your treating physician(s) explaining medical necessity
Clinical guidelines, peer-reviewed literature, or specialty society recommendations supporting the treatment
Referral letters (if your plan requires referrals)
Any previous correspondence with the insurer

Tip: Ask your provider for a succinct appeal-support letter. Physicians’ letters that cite specific clinical data and standards of care carry weight in both internal and external reviews.

Step 5: Write an Effective Appeal Letter

Your appeal letter should be clear, concise, and focused on the clinical facts. Below is a structure you can use.

Appeal Letter Structure (what to include)

Patient identification: name, date of birth, policy number, claim number, dates of service
Statement of action: a one-line description of what you are appealing (e.g., “I am appealing the denial of coverage for [service] on [date]”)
Reason for denial: quote the denial reason from the EOB/denial letter
Clinical justification: clear explanation of medical necessity, referencing medical records and doctor’s letter
Specific request: what outcome you want (e.g., full payment for the claim, reversal of denial)
Attachments list: summarize attachments included
Contact information: phone, email, and authorization to obtain records if needed

Sample appeal paragraph

“On [date of service], Dr. [Name] performed [procedure/test]. This treatment was medically necessary because [brief clinical rationale]. Attached are the clinical notes, diagnostic reports, and a supporting letter from Dr. [Name], which document the severity of the condition and the treatment rationale. I request that you reverse the denial and authorize payment for the services billed under claim number [X].”

Step 6: Submit the Appeal — Methods and Tracking

Most insurers accept appeals online, by mail, or by fax. Choose methods that provide proof of receipt:

Certified mail with return receipt for mailed appeals
Fax confirmation receipts
Secure online portal confirmation screenshots

Document the submission: note the date, the method, the name of the person you spoke with (if any), and the confirmation number. Keep both electronic and hard copies of everything you send.

What to Expect During Internal Review

Internal reviews are often handled by a clinical team and administrative reviewers. The insurer should provide a written response with the decision, the reason for the decision, and information about your rights to further appeal or external review. If the insurer reverses the decision, they will explain how much they will pay and any member liability. If they deny the appeal, the letter should explain how to pursue an external review and provide relevant timelines.

Step 7: If Denied Again — Request an External Review

If the internal appeal is denied and you remain convinced the decision is incorrect, pursue an external review if available. External reviewers are independent and evaluate whether the insurer’s decision is reasonable based on the evidence.

How to request external review

Follow the instructions in the final denial letter to request external review.
Complete any forms required by your state or the reviewer organization.
Submit any additional medical evidence: the external reviewer may accept new information not in the initial appeal.
Be aware that external reviews are generally limited to questions such as medical necessity or whether the treatment is experimental/investigational.

Many states provide a consumer assistance program or an independent review organization to help guide you through external reviews.

Special Considerations for Different Types of Plans

Employer-Sponsored Plans and ERISA

Large employer plans often fall under ERISA. ERISA plans have standardized appeal procedures, but there are nuances: some ERISA plans allow you to bring a legal challenge to federal court only after you have exhausted the internal processes. Working with an attorney familiar with ERISA can be useful for complex or high-value claims.

Medicare and Medicaid Appeals

Medicare and Medicaid have distinct appeal processes. Medicare beneficiaries have several levels of appeal starting with a redetermination by the contractor, while Medicaid processes vary by state. Also, Medicare Advantage plans operate by private insurers and have their own appeal processes—make sure you follow the right path for the program covering you.

Short-Term Plans and Non-ACA-Compliant Plans

Short-term or limited benefit plans may have fewer protections and narrower appeal rights. Carefully review plan documents and state laws that may apply.

Practical Tips When Working with Providers and Insurers

Ask your provider to re-bill or correct coding errors. Many denials result from coding mistakes that your billing office can fix quickly.
Get a letter of medical necessity from your treating physician. Letters that reference diagnostic test results and cite clinical guidelines strengthen your case.
Coordinate with your provider: some providers prefer to appeal on your behalf, and insurers may prioritize provider-initiated appeals.
Use plain language, but include clinical specificity in documentation.
Be persistent: follow up regularly and keep a paper trail of every contact.

Dealing with Urgent or Emergency Situations

For urgent care or emergency services, insurers have accelerated appeal processes. If the denial affects ongoing or urgently needed treatment, clearly label your appeal as urgent and include documentation showing why delay would jeopardize health. Many insurers must respond within 72 hours for urgent claims.

When the Dispute Is About Billing, Not Coverage

Some disputes arise because the provider billed incorrectly (wrong modifiers, duplicate charges) rather than because the insurer improperly denied payment. In billing disputes, insurers and providers may point fingers. Your role is to gather evidence and ask the provider to resubmit corrected claims. If the provider insists the charge is valid, ask for an itemized bill and explanation of the services and codes used.

Balance Billing and Surprise Medical Bills

Balance billing occurs when a provider bills you for amounts not paid by the insurer. The No Surprises Act provides federal protections in many emergency and some non-emergency situations, prohibiting surprise bills in certain circumstances and setting dispute resolution processes. If you receive a surprise bill after an emergency or out-of-network care at an in-network facility, contact your insurer and the provider and reference federal or state protections that may apply.

If Your Claim Is Denied for Experimental or Investigational Treatment

Denials for experimental or investigational treatments are common for novel therapies. You can strengthen an appeal with clinical trial results, published peer-reviewed studies, and letters from specialists explaining why the treatment is appropriate for your particular case. When clinical evidence is limited, involvement from recognized specialty societies or expert medical testimony may help in an external review.

When to Involve a Lawyer or Patient Advocate

Most denials can be handled without legal help. But consider professional assistance when:

The potential financial liability is high (thousands or tens of thousands of dollars)
You suspect wrongful or bad-faith conduct by the insurer
The plan is ERISA-governed and the internal processes are complex
You’ve exhausted internal and external reviews and still face a significant denial

Patient advocates and non-profit consumer assistance programs can be less expensive options for navigation and documentation help. Many state insurance departments and consumer health advocacy groups provide free or low-cost assistance.

How to Prevent Future Denials

Prevention is often faster and less stressful than appeals. Steps you can take:

Verify coverage and network status before receiving care. Call your insurer to confirm coverage for specific services and providers.
Ask whether pre-authorization or referral is required and, if so, obtain it in writing.
Confirm provider billing information (NPI, tax IDs) and that the provider will bill your insurer.
Know your plan’s benefit limits, exclusions, and medical necessity criteria.
Keep copies of all pre-authorization approvals, referrals, and correspondence.

Understanding Appeal Success Rates and What to Expect

Appeal success rates vary by insurer, type of denial, and documentation quality. For example, administrative denials fixed with corrected billing codes are frequently reversed when corrected claims are resubmitted. Denials based on medical necessity can be harder but are often overturned if compelling supporting evidence is provided—particularly in external reviews where independent clinicians evaluate the case.

Sample Timeline for a Typical Appeal

This sample timeline illustrates a common path but remember your insurer’s specific timelines may differ:

Day 0: Receive EOB and denial letter
Day 1–3: Gather documentation, request medical records, speak with provider billing office
Day 3–7: Submit internal appeal with supporting documents
Day 14–30: Receive internal appeal decision (timeline depends on urgency and plan rules)
Day 30–60: If denied again, request external review and submit additional evidence
Day 60–120: External review decision may take weeks to months depending on complexity and state process

Dealing with Claim Denials for Prescription Drugs

Prescription drug denials often cite formulary tiering, prior authorization, step therapy requirements, or non-formulary status. For drug denials:

Ask the prescriber to submit a prior authorization or exception request explaining why alternative drugs are inappropriate.
Provide clinical documentation showing treatment failure or contraindications to formulary alternatives.
Check if your plan has a tiered formulary appeals process or a medication exceptions committee.

Dealing with Denials for Mental Health, Substance Use, and Behavioral Health Services

Mental health and substance use services can be denied for reasons including lack of documentation, failure to meet medical necessity criteria, or limits within the plan. Federal parity laws require that mental health benefits be no more restrictive than medical/surgical benefits. When you believe parity protections are violated, document comparisons between medical and behavioral health coverage and consider contacting your state insurance regulator if parity concerns persist.

Common Mistakes That Reduce Appeal Success

Missing deadlines for internal or external appeals
Submitting incomplete documentation or failing to include physician letters
Using vague or emotional language rather than clear clinical facts
Failing to follow insurer-specific appeal procedures
Not coordinating with the provider’s billing or appeal teams

How to Escalate When the Insurer Won’t Cooperate

If you encounter uncooperative insurers, consider these steps:

File a complaint with your state insurance department. They can investigate insurer practices and provide consumer help.
Use external review where available; it’s an independent mechanism with real power to overturn denials.
Engage a patient advocate, ombudsman, or attorney if the financial stakes are high or if you suspect bad faith.
Contact elected officials or consumer protection groups for systemic issues that affect many people.

Checklist: What to Do Immediately After Getting a Denial

Read the denial letter and EOB fully and note the exact reason for the denial.
Calendar the appeal deadline and any other time limits.
Copy and secure all relevant documents (EOB, bills, records, provider letters).
Contact the provider’s billing or medical records office for help gathering documentation and possibly filing an appeal on your behalf.
Draft the appeal letter using clear, clinical reasoning and attach all supporting evidence.
Submit the appeal with proof of delivery and track ongoing communications.

Frequently Asked Questions (FAQs)

How long will an appeal decision take?

Internal appeal decisions typically take 30–60 days for standard claims and as little as 72 hours for urgent cases. External reviews vary by state but can take several weeks to months depending on case complexity.

Can my provider appeal for me?

Yes, many providers will file appeals on behalf of patients, especially for billing and coding errors. Patients should still maintain their own copies and follow up directly with the insurer.

Will filing an appeal affect my relationship with the provider?

Generally no. Providers expect billing disputes to happen and often prefer to work with patients and insurers to resolve them. If you encounter resistance, consider finding a patient advocate or a different provider for future care.

What if the denial is for a service I already received in an emergency?

Emergency services are often protected under federal and state laws. File an appeal, cite emergency treatment rules, and consider raising the No Surprises Act if balance billing occurs.

Real-World Example (Illustrative)

Consider Jane, who had an MRI for persistent neurological symptoms. The insurer denied payment citing “lack of medical necessity.” Jane requested her medical records, gathered neurologist notes, diagnostic test results, and a supporting letter from her specialist explaining the clinical rationale for the MRI. She submitted an internal appeal with this documentation and requested an expedited review due to ongoing symptoms. The insurer reversed the denial after reviewing the records, and the claim was paid. Jane’s proactive documentation and the specialist’s letter were decisive.

Appealing a health insurance denial is a process that rewards preparation, persistence, and documentation. Start by understanding the denial, follow timelines precisely, gather strong clinical evidence, and use the insurer’s appeal processes. If the internal appeal fails, move to external review and leverage state consumer resources. With the right approach, many denials are reversed—saving you money and ensuring needed care is covered.