Fewer than 1% of denied health insurance claims are appealed — despite the fact that 34% of those that are appealed succeed in reversing the denial under ACA Marketplace plans, and 75% succeed in Medicare Advantage. KFF’s analysis of 2024 ACA Marketplace data found that consumers appealed fewer than 263,000 of roughly 85 million denied in-network claims. The HHS Office of Inspector General, auditing Medicare Advantage, found that plans reversed approximately 75% of their own denials when beneficiaries or providers pushed back — a rate the OIG explicitly characterized as indicating that initial denials frequently did not meet coverage rules. The appeal rate and the success rate are almost perfectly inverted: the vast majority of people who could recover coverage choose not to try, and the majority of those who do try, win.
The mechanism behind both sides is the same: informational asymmetry. Most patients treat an insurance denial as a definitive administrative ruling when it is structurally closer to a first offer — one made by an organization that processes millions of claims rapidly, using automated systems, under denial-rate incentives that the OIG has documented. The 1% appeal rate reflects this misframing. Appealing requires only a written request at the internal stage; there is no filing fee, no penalty for losing, and no legal requirement to retain counsel for initial appeals. The cost is time and documentation. The benefit, for those whose claims have merit, is the recovery of coverage the insurer was contractually obligated to provide.
The limits of this entry matter. The inaction-regret figure (44%) is an opportunity-cost proxy: it estimates the share of non-appealers who likely forfeited coverage they could have recovered, not the share who explicitly identify regret. Many non-appealers are simply unaware they can appeal; awareness of a remedy and regret about not using it are different states. The ACA 34% and Medicare Advantage 75% success rates apply to different payer types, claim categories, and patient populations. Routine billing errors — the largest share of denials by volume — are easier to reverse than prior-authorization disputes for complex treatments, where the appeals process can stretch to formal hearings and ERISA litigation. Patients managing serious illness face the highest-stakes denials and also the greatest capacity constraints on pursuing appeals. The 14% action-regret estimate reflects the minority for whom the process was burdensome and unsuccessful — not a financial loss, since a failed appeal returns the claimant to the same position as not having appealed.