Do appeals work?
Fewer than 0.2% of denied claims are appealed. When they are, roughly one in three wins at internal appeal, and external reviews overturn even more.
Look up any insurer on the insurer rankings to see its own appeal record.
Prior authorization is the other wall
Before certain care (post-acute care, MRIs, specialty drugs) your plan must approve it in advance. KFF's 2026 analysis of insurers covering ~71 million people found plans denied 12-18% of standard prior-authorization requests in 2025. In Medicare Advantage, UnitedHealthcare denied the most standard requests (17%); in ACA marketplace plans, Centene denied the most (25%). Medicare Advantage data on this comes from insurer websites, not a CMS public file: CMS only began requiring standardized public reporting recently, which is why this site cannot yet compute prior-auth rates the way it computes denial rates.