Centene denied 25% of standard prior authorization requests in the ACA marketplace in 2025, the highest rate among the 14 major insurers KFF analyzed in its first look at federally mandated prior authorization data. UnitedHealth denied 17% of Medicare Advantage requests, more than three times the 5% rate at Elevance, according to the same KFF report, published August 13, 2026.
The numbers exist because of a 2024 CMS rule that forced insurers to post prior authorization metrics in public for the first time. Practices now have a way to see, insurer by insurer, who says no most often and who reverses those denials on appeal. That data changes how a billing team should decide where to spend follow-up time.
The first year of mandatory reporting
Insurers covering Medicare Advantage, Medicaid managed care, and ACA marketplace plans had to post their 2025 prior authorization numbers by March 31, 2026, under a CMS interoperability rule finalized in 2024. KFF pulled data from 14 insurers covering about 71 million enrollees and found denial rates of 12% for standard Medicare Advantage requests, 14% for Medicaid managed care, and 18% for ACA marketplace plans. Expedited requests fared slightly better: 10% denied in Medicare Advantage, 12% in Medicaid managed care, and 16% in the ACA marketplace.
Coverage of each market varied. The six Medicare Advantage insurers KFF reviewed represent 25 million enrollees, or 69% of that market. The eight Medicaid managed care insurers cover more than 35 million enrollees, about 54% of the market. The eight ACA marketplace insurers cover 11 million enrollees, roughly 74% of the 28 states using the federal marketplace. Healthcare Dive's review of the same data put it plainly: at least 1 in 8 standard prior authorization requests across all three markets ended in a denial in 2025.
Denial rates swing hard by insurer
Market averages hide how differently individual insurers behave. In Medicare Advantage, Elevance denied 5% of standard requests while UnitedHealth denied 17%. In Medicaid managed care, L.A. Care denied 2% while Independence Health Group denied 23%. In the ACA marketplace, GuideWell denied 3% while Centene denied 25%, with UnitedHealth close behind at 21%.
| Market | Lowest denial rate | Highest denial rate |
|---|---|---|
| Medicare Advantage | Elevance, 5% | UnitedHealth, 17% |
| Medicaid managed care | L.A. Care, 2% | Independence Health Group, 23% |
| ACA marketplace | GuideWell, 3% | Centene, 25% |
Source: KFF, "Prior Authorization Metrics Provide New Insights into Insurer Practices, but Gaps Remain," August 13, 2026.
For a billing company or practice manager tracking multiple payer contracts, that spread matters. A practice sending the same volume of requests to Independence Health Group and L.A. Care should expect roughly ten times the denial rate from one versus the other, before appeals even enter the picture.
Appeals overturn most denials
Denied does not mean final. KFF found that 67% of appealed Medicare Advantage denials were overturned, along with 47% of Medicaid managed care denials and 43% of ACA marketplace denials. Individual insurers ranged even wider on overturn rates: Medicare Advantage appeals succeeded 40% of the time at Kaiser Permanente versus 93% at Centene, Medicaid appeals succeeded 22% of the time at CVS versus 81% at UnitedHealth, and ACA marketplace appeals succeeded 16% of the time at HCSC versus 54% at Centene.
Centene shows up on both ends: it denies the most ACA marketplace requests up front, and it overturns more than half of what gets appealed. That combination points to a practical rule for billing staff deciding which denials to fight: check the specific insurer's overturn rate before writing off a denial as unwinnable.
A faster clock for decisions, starting in 2026
Median response times reported for 2025 already look fast on paper. Standard requests took a median of 0.9 days across Medicare Advantage, Medicaid managed care, and ACA marketplace plans. Expedited requests took a median of 0.4 days in Medicare Advantage, 0.8 days in Medicaid managed care, and 1 day in the ACA marketplace. KFF cautions that medians can mask outliers, since insurers report averages and medians but not how often they miss the deadline entirely.
A separate, related CMS requirement sets a hard ceiling going forward: starting January 1, 2026, impacted Medicare Advantage, Medicaid, and CHIP plans must decide standard prior authorization requests within seven calendar days and expedited requests within 72 hours. A follow-on requirement for payer-side prior authorization APIs takes effect January 1, 2027. Billing teams that track how long a payer actually takes, not just the deadline on paper, will have an easier time flagging violations before a claim ages into a bigger problem.
What the public data still hides
KFF flags real gaps in what insurers report. Plans post percentages but not the underlying counts, so a practice cannot tell whether a 5% denial rate came from 50 requests or 50,000. No insurer breaks its numbers down by service type, so a high overall denial rate could reflect one imaging category rather than a general pattern. Reporting formats are not standardized, which makes side-by-side comparison harder than it should be, and appeal reasons are not disclosed at all.
Even with those gaps, the first year of data gives practices something they did not have before: a public, insurer-specific denial and appeal record to check against their own claims experience. A practice whose internal denial rate with a given payer runs well above that payer's published number has a concrete figure to raise in a payer meeting, rather than a general complaint about slow payment.
Sources
- KFF, "Prior Authorization Metrics Provide New Insights into Insurer Practices, but Gaps Remain," August 13, 2026
- Healthcare Dive, "Prior authorization denials vary widely among insurers," August 14, 2026
- CMS, "CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F)"
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