Why insurers deny claims — and why most denials aren't the final word
When your insurer sends you an Explanation of Benefits (EOB) marked "denied," it means their automated system or a claims reviewer determined that the claim didn't meet a specific rule in your policy at that moment. The critical word is "moment." Most denials are not permanent legal judgments — they are initial administrative decisions made quickly, often by algorithms, without full context about your medical situation. That is why the appeals process exists and why it regularly works.
Denials fall into a few predictable buckets. The most common are: the service was deemed not "medically necessary" by the insurer's criteria; a prior authorization wasn't obtained before the procedure; the provider was out-of-network; the claim was coded incorrectly on submission; or your insurer says the treatment is "experimental" or "investigational." Each of these denial types has a different — and quite specific — pathway for appeal, which is why knowing your denial code from the EOB is the most important first step.
Federal law under the Affordable Care Act gives you a guaranteed right to at least one internal appeal (reviewed inside the insurer) and, after that, an external appeal reviewed by an independent organization. Many people don't realize the external appeal exists, or assume appealing is futile. The evidence says otherwise: studies of external appeal outcomes consistently show consumers winning 40–60% of the time when they reach that stage.
A denied claim isn't always the same problem
The reason your claim was denied shapes exactly what you need to do next — and the strategy that works for one denial type can be irrelevant for another.
What happens if you let a denial stand
If you do nothing, the denial becomes final. You'll be on the hook for the full billed amount — which, depending on the service, can range from a few hundred dollars to tens of thousands. Providers may send the balance to collections while you wait, which can damage your credit. More importantly, if the denied service is ongoing care — a medication, a therapy, a specialist visit — you may be forced to choose between going without treatment and paying out of pocket indefinitely. Neither outcome is acceptable when a formal, federally protected appeals process exists and costs you nothing to use.
A 2023 analysis by the Kaiser Family Foundation found that marketplace insurers denied an average of 17% of in-network claims — but fewer than 1 in 10 affected patients filed a formal appeal. Among those who did appeal internally, roughly 41% had their denial overturned. The appeals process works, but only if you use it.
There is a trusted solution for this.
We've mapped out the complete appeal process — internal and external — including what to put in your letter, which documentation your insurer is required to provide you, and when to escalate to your state insurance commissioner.
See the Trusted Solution →Free to read · Independently verified · Updated March 2026
What others have experienced
214 community experiences-
RK
My insurer denied a $4,200 MRI as "not medically necessary" even though my neurologist ordered it after two years of symptoms. I filed an internal appeal with a letter from my doctor explaining the clinical rationale and attaching my symptom history. Six weeks later they reversed it in full. The key was getting my doctor to write something specific — not just "patient needs this" but actually citing the clinical guidelines that supported the order.
87 found this helpful -
TM
Got hit with a surprise bill after an ER visit — the ER was in-network but the on-call surgeon who treated me was out-of-network, which I only found out afterward. The initial claim denial was for over $11,000. I cited the No Surprises Act in my appeal letter and requested that the insurer apply in-network cost-sharing. They pushed back once, but I escalated to my state's insurance department and filed a complaint. Resolved in my favor within 30 days of the complaint — paid my in-network deductible and nothing more.
124 found this helpful -
DW
My claim for an outpatient mental health treatment program was denied — the insurer said the level of care wasn't appropriate and I could be treated in a lower-intensity setting. My therapist disagreed strongly. I requested the clinical criteria the insurer used to make that determination (you have a right to this under federal law) and found that they were applying a more restrictive standard than they use for comparable medical conditions. I cited the Mental Health Parity and Addiction Equity Act in my appeal. Took two rounds and three months, but they reversed it. Don't give up just because the first appeal fails.
103 found this helpful
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