Insurance Appeals
How to Appeal an ACA Insurance Denial: Your Complete Guide
Your ACA marketplace plan denied a claim — but that doesn't mean the fight is over. This guide walks you through every step of the appeal process so you can get the coverage you're paying for.
Why ACA Plan Denials Happen — and Why You Should Always Appeal
If your ACA marketplace health plan denied a claim, you are far from alone. Studies consistently show that roughly one in five in-network claims are initially denied by insurers. Yet fewer than 1% of patients ever file an appeal — which means millions of people leave money and medical care on the table every year.
The good news? When people do appeal, they win at a surprisingly high rate. Internal appeals succeed roughly 40-60% of the time depending on the state and the type of denial. External reviews — where an independent third party overrules your insurer — overturn denials in about 40% of cases nationally.
Under the Affordable Care Act, every marketplace plan sold through HealthCare.gov or a state exchange must give you the right to appeal. This isn't optional for insurers — it's federal law. The process is free, and you don't need a lawyer to do it (though one can help in complex cases).
💡 Key Stat
Fewer than 1% of denied claims are appealed, but those that are win 40-60% of the time. The odds are in your favor if you take action.
Common ACA Insurance Denial Types
Understanding why your claim was denied is the first step toward a successful appeal. Here are the most common denial reasons for ACA marketplace plans:
Not Medically Necessary
Your insurer's medical reviewers decided the treatment, procedure, or medication isn't required for your condition. This is the most common denial reason — and also the most commonly overturned on appeal, especially when your doctor provides a strong letter of medical necessity.
Prior Authorization Not Obtained
Your provider didn't get pre-approval before performing a procedure. In many cases you can appeal on the grounds that the service was urgent, you weren't informed about the requirement, or the treatment would have been approved if authorization had been sought.
Out-of-Network Provider
You received care from a provider outside your plan's network. Under the No Surprises Act and ACA protections, many surprise out-of-network bills — especially for emergency services — can be appealed and resolved in your favor.
Service Not Covered
The insurer says the service isn't included in your plan benefits. Because ACA plans must cover 10 essential health benefits, this denial is sometimes made in error. Verify whether the service falls under a required category before accepting the denial.
Coding or Billing Errors
A surprising number of denials are simply clerical — the wrong CPT or diagnosis code was submitted. Ask your provider to resubmit with corrected codes before escalating to a formal appeal.
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Calculate Your 2026 Premium Impact →The ACA Two-Level Appeal Process
The Affordable Care Act guarantees a two-stage appeal process for every marketplace plan. Understanding these stages — and their deadlines — is critical.
Level 1: Internal Appeal
Your insurance company must re-review the denial using a different reviewer than the one who made the original decision. You have 180 days from the denial date to file.
- Submit a written appeal letter explaining why the denial is wrong
- Include supporting documents: your doctor's letter of medical necessity, medical records, clinical guidelines, and any relevant peer-reviewed studies
- The insurer must respond within 30 days for pre-service claims or 60 days for post-service claims
- For urgent cases (life-threatening conditions), request an expedited appeal — the insurer must respond within 72 hours
Level 2: External Review
If your internal appeal is denied, you can request an external review by an independent, accredited organization. You have 4 months from the internal appeal denial to request this.
- The external reviewer is completely independent of your insurance company
- Their decision is legally binding on the insurer — if they rule in your favor, your insurer must comply
- External reviews are decided within 45 days (or 72 hours for expedited cases)
- There's no cost to you for requesting an external review
How to Write a Winning Appeal Letter
Your appeal letter is the most important document in the process. Here's what to include:
📋 1. Reference Your Claim Details
Include your name, member ID, claim number, date of service, and the specific denial reason from your Explanation of Benefits (EOB).
📝 2. State Your Case Clearly
Explain in plain language why the denial is wrong. Reference your plan's Summary of Benefits and Coverage (SBC) and show how the service should be covered under your plan terms.
🏥 3. Include Medical Evidence
Attach your doctor's letter of medical necessity, relevant medical records, clinical practice guidelines from medical associations, and any published studies supporting the treatment.
⚖️ 4. Cite ACA Requirements
If the denied service falls under one of the ACA's 10 essential health benefits, say so explicitly. Reference the specific benefit category and explain why your plan is required by law to cover the service.
📄 Need Appeal Letter Templates?
For detailed appeal letter templates and state-by-state deadline guides, visit our sister site Insurance Appeal Guide. It covers every type of insurance denial — from medical necessity to prior authorization — with free, ready-to-use letter templates and step-by-step instructions tailored to your state's regulations.
7 Tips to Maximize Your Chances of Winning
Act quickly. Even though you have 180 days, filing sooner keeps the details fresh and gets you a resolution faster.
Get your doctor involved. A letter of medical necessity from your treating physician is the single most powerful piece of evidence you can submit.
Request your complete claim file. You have the legal right to see every document your insurer used to make the denial decision.
Check for billing errors first. Call your provider's billing department — a simple code correction can resolve the issue without a formal appeal.
Keep detailed records. Log every phone call (date, time, representative's name, what was said) and save copies of all correspondence.
File a complaint with your state insurance commissioner. This doesn't replace an appeal but adds regulatory pressure. Some states resolve complaints faster than formal appeals.
Use the Subsidy Calculator to check your numbers. If your denial relates to subsidy amounts or cost-sharing, verify the correct figures and include them in your appeal.
Frequently Asked Questions
How long do I have to appeal an ACA insurance denial?
Under the ACA, you have at least 180 days (6 months) to file an internal appeal after receiving a claim denial from your marketplace plan. If the internal appeal is denied, you then have 4 months to request an external review by an independent third party.
What is the difference between an internal appeal and an external review?
An internal appeal is reviewed by your insurance company — someone other than the person who made the original denial decision. An external review is conducted by an independent organization that has no ties to your insurer. The external reviewer's decision is binding on the insurance company.
Can I appeal if my ACA plan says a treatment is not medically necessary?
Yes. 'Not medically necessary' is one of the most common denial reasons and one of the most frequently overturned on appeal. Ask your doctor to write a letter of medical necessity explaining why the treatment is required for your condition, citing clinical guidelines and peer-reviewed evidence.
Does the ACA guarantee my right to appeal a denied claim?
Yes. The Affordable Care Act requires all marketplace plans to provide an internal appeals process and access to an external review. These protections apply to all non-grandfathered health plans, including every plan sold through HealthCare.gov and state exchanges.
The Bottom Line
An insurance denial is not a final answer — it's the start of a conversation. The ACA guarantees your right to a fair appeal, and the statistics are on your side. Whether your claim was denied for medical necessity, prior authorization, or a billing error, the two-level appeal process gives you multiple bites at the apple.
Start by understanding the denial reason, gathering your documentation, and filing your internal appeal. If that doesn't work, take it to external review. And remember — for detailed templates, state-specific deadlines, and step-by-step appeal guides, our sister site Insurance Appeal Guide has everything you need to fight back.
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⚠️ Disclaimer
This calculator provides estimates for educational purposes only. It is not a substitute for professional advice. Actual premiums, subsidies, and eligibility may vary based on your specific circumstances, location, and available plans. We are not licensed insurance agents or brokers. For official information, visit HealthCare.gov or contact a licensed insurance professional. This site is not affiliated with the U.S. government, CMS, or any insurance company.