Picture the scene. It's a Tuesday night. The denial letter is on the kitchen table — dense type, a code you don't recognize, a dollar figure that makes your stomach drop. Your first instinct is that the decision is final. It isn't. The appeals process is a second trial your insurer hoped you'd never file, and the statistics say you should file it.
Fewer than 1% of denied marketplace claims are ever appealed, per KFF's analysis of federal data. But roughly a third of internal appeals are overturned — insurers reversed their own denials in 34% of cases in 2024. In Medicare Advantage prior authorization disputes, KFF found 67% of appeals succeed. In Medicaid managed care, 47%. In the ACA marketplace, 43%. The gap between those two numbers — the tiny fraction who appeal and the large fraction who win — is the most expensive information asymmetry in American healthcare.
Under the Affordable Care Act, you have the right to an internal appeal, and you have 180 days from the denial notice to file it. That's six months, but don't treat it as generous. Evidence goes stale, deadlines compound, and the insurer's clock starts when you act.
Your appeal letter needs three things. First, the facts: your name, policy number, claim number, date of service, and the specific denial reason from the Explanation of Benefits. Second, the argument: why the denial is wrong, mapped to the insurer's own stated reason. If they denied for lack of medical necessity, your argument is your doctor's letter saying it was necessary. If they denied for lack of prior authorization, your argument is the authorization number, the fax confirmation, the phone log. Third, the evidence: the clinical notes, the prior authorization approval, the referral, the peer-reviewed guideline supporting the treatment. Organize it like a case file, because that is what it is.
Get your doctor's office involved early. A one-page letter of medical necessity from the treating physician — specific to your case, citing your records, not a form letter — is the single most effective document in an appeal file. Insurers are required to have the appeal reviewed by someone who wasn't involved in the original denial. Make that person's job easy: give them a file where the right answer is obvious.
If the internal appeal fails, you are not done. The ACA gives you the right to an external review by an independent third party — typically through your state insurance department or a federally designated reviewer. This is the step that changes the power dynamic: the reviewer doesn't work for your insurer.
In 2024, marketplace enrollees filed at least 5,881 external appeals — just 4% of upheld internal appeals, per KFF. That underutilization is staggering, because external reviewers have no institutional loyalty to the denial. The process is free to you. The deadlines vary by state, but they're typically short — often 60 days to four months from the final internal denial. Mark the date the moment the internal appeal concludes.
Your external review file should include everything from the internal appeal plus the insurer's final denial letter and their stated rationale. The reviewer reads the whole record fresh. Cases that died internally on a technicality sometimes live here on the merits.
Winning appeals is a documentation discipline. Start a file the day the denial arrives: the denial letter, the EOB, every piece of correspondence, and a dated log of every phone call — who you spoke to, the reference number, what they said. Insurers' phone records are their records. Yours are yours.
Three documentation moves separate successful appeals from unsuccessful ones. Get the denial reason in writing and match your evidence to it exactly — an appeal that argues medical necessity when the denial was actually about timely filing loses before it's read. Obtain the insurer's clinical criteria: plans must disclose the guidelines they used, and many denials collapse when measured against the plan's own published standards. And build the paper trail upward — if your doctor's first letter was general, ask for a second one that rebuts the denial point by point.
Watch for the patterns that signal a winnable fight. Denials coded "Other" — 36% of marketplace denials in 2024 — with no specific reason are often the weakest; the insurer hasn't articulated a defense. Denials for services your plan document covers, denied on administrative grounds, reverse at high rates when the paperwork is corrected. And any denial where the clinical facts are on your side and the appeal overturn data says so — remember that two-in-three figure in Medicare Advantage — deserves to be fought.
Most appeals don't need a lawyer. They need persistence and paper. But bring in help when the dollar amount is large, when the denial involves an ongoing course of treatment — cancer care, a surgery your doctor says can't wait — or when the insurer has denied the same service repeatedly.
Your state insurance department's consumer assistance office is free and underused. Patient advocacy organizations — the Patient Advocate Foundation, state health insurance assistance programs — handle denial appeals routinely. For employer-plan denials governed by ERISA, the rules are stricter and the stakes higher; that's where an attorney who handles insurance bad-faith work earns the fee. Many take clear-cut wrongful denial cases on contingency.
The denial letter on your kitchen table is an opening position, not a verdict. The insurers know the appeal statistics — they built the process. Now you know them too.
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