How often are health insurance denials overturned on appeal?

In California, independent physician reviewers overturned 65.2% of 11,573 denials that reached Independent Medical Review in 2021-2025. But the overall figure hides a very wide range: by treatment class it runs from about 12% to about 98%. Every figure counts only denials that were appealed all the way to external review, which is fewer than 1% of denials.

Which insurance denials are most likely to be overturned?

Among California treatment classes with at least 30 decisions in 2021-2025, viscosupplementation injections were overturned most often at 97.7%, followed by other classes in the high eighties. At the other end, knee replacement and inpatient discharge disputes were overturned least often, near 12%. The spread is the finding: an overall average tells you very little about any particular denial.

Has the insurance denial overturn rate changed over time?

Yes, substantially. In California it rose from 35.1% in 2002 to 72.4% in 2025 — roughly double. This record shows the outcomes but cannot establish the cause: it holds no information about who chose to appeal, how plans changed their own review behaviour, or how the state's process evolved.

Findings · California · 2021-2025

The overturn rate is not one number

65.2% of appealed denials were overturned in California in 2021-2025. That figure is quoted often and it is nearly useless on its own, because it averages a range that runs from about 12% to about 98% depending on what was denied. Five findings from 42,621 published decisions, all free to read and cite.

What was denied matters more than anything else

finding 1

Every class below holds at least 30 decisions in 2021-2025. The top of this list and the bottom describe the same appeal process, in the same state, in the same years.

Overturned — the reviewer did not sustain the denial
Upheld — the reviewer sustained the denial

MOST OFTEN OVERTURNED

LEAST OFTEN OVERTURNED

⚠ This is not evidence that one class of denial is decided better than another. Different treatments carry different evidence bases, and a class where the published guidance is clear will produce different outcomes from one where it is contested — on both sides. What the spread does establish is that a single national overturn figure cannot describe any particular denial.

The rate has roughly doubled since 2002

finding 2

35.1% of appealed denials were overturned in 2002. In 2025 it was 72.4%. Each point is a full year of published decisions, and years with fewer than 30 are not plotted.

Hover the chart for a year’s counts. Series stops at 2025 — report year 2026 uses a different category vocabulary.

We cannot tell you why, and no one should claim otherwise from this record.

This holds outcomes. It does not hold who chose to appeal and who gave up, how plans changed their own review behaviour, how the Department’s process or its published fields evolved, or how the mix of disputed treatments shifted as new and expensive therapies arrived. Every one of those could move this line, and several probably did. A study that picked one and called it the cause would be the most quotable and the least defensible thing on this site.

On the hardest question, reviewers disagree with each other more often than not

finding 3 · published nowhere else

Where the dispute is whether a treatment is established enough to be a covered benefit at all, California assigns a panel of three reviewers and publishes their vote. 1,053 of 1,931 panels (54.5%) split 2–1 in 2021-2025.

Panel split 2-154.5%1,053
Unanimous 3-045.5%782

⚠ A dissent is not an error, and this is not a claim that either side of a split was right. It is the only place in California’s published record where one reviewer’s disagreement with another is visible — and on this question it is more common than agreement. Medical-necessity disputes are decided by a single reviewer, so no comparable figure exists for them. The full breakdown.

The question the plan sends to review changes the outcome

finding 4

A plan can deny a treatment as not medically necessary, or as experimental. In the 11 treatment classes where both characterisations reach 30 decisions in 2021-2025, medical-necessity disputes were overturned more often in 9, by 11.8 points on average.

Treatment class	Medical necessity	Experimental	Gap
Radiation Therapy	78.8% of 33	45.0% of 40	+33.8
Proton Beam	59.1% of 115	29.3% of 41	+29.9
Weight Control	87.7% of 1,383	66.7% of 51	+21.0
Biologics	83.4% of 349	65.1% of 43	+18.3
Genetic/Genomic Test	67.8% of 59	49.6% of 254	+18.2
Radiofreq Ablat	68.8% of 48	52.7% of 74	+16.0
Cancer Rx	49.4% of 83	41.0% of 61	+8.4
CT Scan	34.6% of 81	32.4% of 34	+2.2
Other	51.9% of 720	51.2% of 531	+0.7
Nerve Block	64.7% of 51	73.9% of 92	-9.2
IVIG Therapy	59.6% of 109	69.2% of 39	-9.6

⚠ These are different disputes, not the same dispute asked twice: a treatment denied as experimental is often genuinely newer or less settled. The gap describes what reviewers decided; it does not show that changing the characterisation changes the result, and nothing here suggests what anyone should argue.

Expedited review is far faster, and the outcomes land close together

finding 5

Expedited reviews in 2021-2025 were decided in a median of 5 days, against 21 for standard reviews. 64.3% of 5,180 expedited reviews were overturned, and 66.0% of 6,393 standard ones.

Expedited — overturned64.3%5,180
Standard — overturned66.0%6,393

⚠ Urgent cases are not the same cases, so this is not the effect of asking for expedited review — it is what the two groups did. California grants expedited review on the urgency of the condition, and the DMHC Help Center (1-888-466-2219) can say whether a case qualifies.

Read this before quoting any number above. Every figure counts only denials that were appealed all the way to independent review. Fewer than 1% of denials are appealed internally at all, so “65.2% overturned” is not the share of denials that are wrong — it is the share of contested denials that reviewers did not sustain. California only, and only plans the state regulates: not self-funded employer plans, Medicare or Medicaid.

Cite this

Claim Appeal Data, "Insurance denial overturn rates by treatment class" (2026-09-04). Analysis of 42,621 published California Independent Medical Review decisions, 2001–2025. https://claimappealdata.com/findings/

Underlying data: California Department of Managed Health Care, Independent Medical Review (IMR) Determinations, Trend, via the CalHHS Open Data Portal, published under Health & Safety Code § 1374.33(g). Modified from the published file; not official government data. How these numbers were made · who publishes this · report an error.