Health insurers on the ACA marketplace denied 19% of in‑network claims in 2024, with rates ranging from 13% to 35%. The figure means about 85 million denials nationwide, a number that rattles consumers and regulators alike.

Blue Cross Blue Shield of Alabama topped the list at 34.8%, while United Health followed at 33.3%. These rates suggest that the insurer chosen can triply raise denial odds, even when plan size or network breadth differ.

Only 5% of denials stemmed from medical necessity disputes; the bulk arose from administrative gaps or unexplained “other” categories. Appeals were rare, under 1%, and two‑thirds of those appeals upheld the original denial, cementing the finality of most rejections.

This data, sourced from KFF’s Transparency in Coverage analysis, exposes the fragmented nature of claim processing. It shows that insurer identity, not plan size, is the decisive factor for patients seeking timely payment.