KFF found that ACA Marketplace insurers denied 19% of the 451 million in-network claims they received in 2024, about 85 million claims. The largest single reason code was "other" at 36% of denials, and administrative reasons came next at 25%, so most denials trace to causes a practice can check before it submits.
KFF published the analysis on March 24, 2026. It uses the CMS Transparency in Coverage public use file for the 2024 plan year and covers 157 reporting insurers. The data cover Marketplace plans only, not Medicare, Medicaid, or employer coverage.
How many claims did insurers deny in 2024?
Insurers received about 496 million claims in 2024. In-network claims made up 451 million of them (91%), and out-of-network claims made up 44 million (9%).
The in-network denial rate was 19%. The out-of-network rate was 37%, nearly double. KFF reports a combined average of 20% across all claims, because in-network claims dominate the volume.
The spread between insurers is wide. In-network denial rates ran from 3% to 36% across the 157 insurers in the file. A practice that sees a 15% denial rate from one payer and 4% from another is looking at a normal range for this market.
Why were the claims denied?
KFF grouped in-network denials by the reason code the insurer reported. The table shows each reason as a share of denied in-network claims.
| Reason reported | Share of denied in-network claims |
|---|---|
| Other (unspecified) | 36% |
| Administrative reasons | 25% |
| Excluded service | 13% |
| No prior authorization or referral | 9% |
| Medical necessity | 5% |
Source: KFF, "Claims Denials and Appeals in ACA Marketplace Plans in 2024," March 24, 2026. The five listed reasons add up to 88%.
Medical necessity accounts for 5% of denials. Administrative reasons and missing prior authorization or referral together account for 34%. Those two groups map to front-desk and authorization work.
The 36% "other" group is the biggest and the least useful. An insurer that reports a denial as "other" gives the practice no category to fix, so staff must read the remittance code on each claim.
How much do denial rates vary?
KFF found a spread by state as well. Hawaii had the highest state average denial rate at 27%. South Dakota had the lowest at 7%.
The top of the range shrank between years. In 2023, 17% of reporting insurers had denial rates of 30% or more. In 2024, only 3% did.
A practice should not set its own target from a national average alone. Compare each payer against its own history first, then against the 19% in-network figure. A payer that moves from 8% to 14% in one year has changed something, such as a claim edit or an authorization list, and the practice can trace it by reason code.
Out-of-network claims follow a different pattern. At 37%, the out-of-network denial rate was 18 points above the in-network rate of 19%. A practice with a large out-of-network share will see a higher blended rate than one that bills in-network only.
What happens when a practice appeals?
Few denials reach an appeal. KFF counted at least 262,982 internal appeals in 2024, which is fewer than 1% of denied claims. Insurers upheld their original decision in 66% of those appeals.
Fewer still go to an outside reviewer. KFF found at least 5,881 external appeals, which equals 4% of the internal appeals that insurers upheld.
A separate study shows what outside review can change. Researchers from Brown University, the University of Texas at San Antonio, and the University of Chicago analyzed about 51,000 external appeal cases in New York State from 2019 to 2025. The study appeared in JAMA and Healthcare Dive reported it in April 2026. The share of denials overturned rose from 38% in 2019 to almost 53% in 2025.
Overturn rates differed by service. Home health denials were overturned more than 78% of the time. Prescription drug and dental denials were each overturned more than 50% of the time. These are New York cases, and the sample includes only denials that reached external review.
Which front-end errors cause denials in ambulatory care?
Inovalon surveyed more than 400 revenue cycle leaders and released results on August 13, 2026. Among ambulatory organizations, 33% named eligibility as the leading driver of denials. Another 19% named patient registration.
Acute care leaders gave a different mix. Eligibility led there too at 28%, followed by prior authorization at 23%. Post-acute organizations named missing or invalid claim data first at 22%, then prior authorization at 21% and eligibility at 18%.
Inovalon also asked about leadership priorities. Of the executives surveyed, 46% cited denials as the top revenue cycle challenge. Among managers, 38% did.
KFF shows that administrative and authorization reasons cover 34% of denied Marketplace claims, and Inovalon shows that eligibility and registration cover 52% of ambulatory denial drivers. Both sets of numbers describe work done before the claim leaves the practice. Eligibility checks at scheduling and again on the day of the visit are the usual control for the first group.
Numbers to track from this data
- Your in-network denial rate by payer, against the 19% KFF figure for Marketplace plans.
- The share of denials with an unspecified reason, against 36%.
- The share of denials that you appeal, against fewer than 1% in the KFF file.
- Your overturn rate on the appeals you file, against 66% upheld in KFF's data.
Sources
- KFF, Claims Denials and Appeals in ACA Marketplace Plans in 2024, March 24, 2026
- Healthcare Dive, report on a JAMA study of New York external appeals, April 15, 2026
- Inovalon, New Inovalon Research Identifies Preventable Drivers of Claim Denials and Prior Authorization Delays, August 13, 2026
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