ACA Marketplace Plan Claim Denied? Your Appeal Rights Explained

Buying health insurance through the ACA marketplace — whether at HealthCare.gov or your state's own exchange — comes with some of the strongest appeal rights in the U.S. insurance system. If your marketplace plan denied a claim, Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization request, or coverage determination, federal law guarantees you a multi-level appeal process, including independent External Independent Review: Complete Guide" class="auto-link">external review. Here is exactly how to use it.

Why ACA Marketplace Plans Deny Claims

ACA marketplace plans are required by 42 U.S.C. § 18022 to cover the ten essential health benefits: outpatient services, emergency care, hospitalization, maternity and newborn care, mental health and substance use treatment, prescription drugs, rehabilitative services, lab services, preventive care, and pediatric services. Despite this mandate, denials are common and fall into predictable categories.

Medical necessity denials: The insurer claims the treatment was not medically necessary under its own internal clinical guidelines — even when your treating physician recommends it and the service falls within an essential benefit category.

Out-of-network disputes: You received care from a provider the plan considers out-of-network, even though you believed they were in-network or had no reasonable in-network alternative. The No Surprises Act (effective January 1, 2022) protects against many out-of-network surprise bills and balance billing situations.

Prior authorization failures: A service required pre-approval that was not obtained or was denied before treatment — including cases where the provider failed to obtain authorization or where the authorization process was unclear.

Benefit limit disputes: The service exceeded a quantity or frequency limit allowed under the plan, or the plan claims the service was already covered under another code.

Exclusion disputes: The insurer claims the service is excluded from coverage — a frequent source of wrongful denials when the exclusion is applied more broadly than the plan documents support.

How to Appeal

Step 1: Read your EOB)" class="auto-link">Explanation of Benefits and denial notice carefully

The denial notice must identify the specific reason code, the plan provision relied upon, and your appeal rights. Under the ACA, all marketplace plans must provide this information in plain language. Identify whether the denial is a medical necessity determination, a prior authorization issue, a network dispute, or an exclusion argument — the answer determines your evidence and legal arguments.

Step 2: File an internal appeal with your insurance company

You have 180 days from the date of your denial notice to file an internal appeal (45 CFR § 147.136). Submit it in writing, include all supporting documentation, and keep a copy of everything. Your insurer must respond within 30 days for pre-service (prospective) denials and 60 days for post-service (retrospective) denials. For urgent situations, the insurer must decide within 72 hours.

Step 3: Obtain a detailed physician letter for medical necessity denials

If your claim was denied as not medically necessary, your treating physician must write a detailed letter — not a general endorsement, but a clinical explanation of why the denied service is appropriate for your specific condition, what alternatives were considered and why they were insufficient, and how the service meets the plan's medical necessity criteria. Request the insurer's specific clinical criteria used in the denial decision.

Step 4: Use the No Surprises Act for out-of-network disputes

Under the No Surprises Act (26 U.S.C. § 9816), surprise bills from out-of-network providers in emergency situations or from out-of-network providers at in-network facilities are protected. If your denial involves out-of-network billing in a covered situation, cite this law directly in your appeal.

Step 5: Request an external review if the internal appeal is denied

After exhausting internal appeals (or in urgent situations, simultaneously), you can request an independent external review under 45 CFR § 147.138. External reviewers — called IROs) Explained" class="auto-link">Independent Review Organizations (IROs) — are accredited and independent of your insurer. They review the denial on its clinical and contractual merits. External reviews overturn insurer denials at approximately 40 to 50 percent rates. This step is free to you under the ACA.

Step 6: File a marketplace appeal for enrollment and eligibility disputes

If you believe you were wrongly denied enrollment, tax credits, or cost-sharing reductions, file a separate appeal with the Health Insurance Marketplace itself. The Marketplace Appeals Center at HealthCare.gov handles these disputes (distinct from medical claim denials). File a complaint with your state insurance department as well — state regulators have authority over the insurer's claims practices even for federal marketplace plans.

What to Include in Your Appeal

• Copy of the denial notice with the specific reason code and plan provision cited
• Your treating physician's detailed letter addressing the specific medical necessity criteria
• Clinical guidelines from professional medical societies supporting the denied service
• Evidence that the service falls within an essential health benefit category under the ACA
• No Surprises Act citation and supporting documentation for out-of-network billing disputes

Fight Back With ClaimBack

ACA marketplace plans offer some of the best appeal rights in the American healthcare system — but most people never use them. The external review process in particular has meaningful success rates, and the entire process is free to you. ClaimBack helps you build a complete appeal letter using the ACA's own framework to argue for the coverage you are entitled to. ClaimBack generates a professional appeal letter in 3 minutes. Start your free claim analysis → Free analysis · No credit card required · Takes 3 minutes

Related Reading

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs External Insurance Appeal