Why Health Insurance Claims Get Denied
A denial notice should state a reason and describe the available review process. Start with that language because different reasons can require different records or correction paths.
Start with the reason, not the amount
The instinct on receiving a denial is to look at the dollar figure. The useful information is the reason code and the sentence next to it. Two denials for the same amount can require completely different responses, and sending the wrong kind of appeal wastes weeks of a window that is already running.
Find the reason on the Explanation of Benefits or the denial letter itself. Then match it to one of the categories below.
Administrative and coding errors
This is the largest and least dramatic category, and the best news when you find it. The service was covered, the patient was eligible, and something in the paperwork was wrong: a transposed member number, a diagnosis code that does not link to the procedure code, a missing modifier, the claim sent to the wrong payer.
Some administrative denials may have a corrected-claim or reconsideration path. Ask the plan and provider whether that path is available, whether an appeal is still required, and how any deadline is affected; do not assume one process preserves another.
What to do: call the plan first and ask specifically what would have to change for the claim to process. Then call the billing office and relay it. Ask both whether a corrected claim resubmission is possible instead of an appeal.
Not medically necessary
This is the category people find most insulting, and the one where appeals matter most. The plan is saying that based on its clinical criteria, the service was not warranted for your documented condition.
The critical thing to understand is what the reviewer actually sees. They are not evaluating you. They are comparing the documentation submitted against a written clinical policy. If the documentation does not show what the policy requires, the denial follows almost mechanically — even when the care was obviously appropriate.
What to do: request the plan's clinical criteria for that service in writing. For many employer group health claims, Department of Labor guidance describes access on request to relevant claim documents. Ask what rule applies to your coverage, then ask the treating provider what clinical documentation, if any, is appropriate to submit.
Prior authorization missing or denied
Some services require approval before they happen. If that approval was never obtained, or was requested and refused, the claim gets denied regardless of medical merit.
If authorization was not sought, the plan terms and facts determine the available correction path and member responsibility. If a request was submitted, its confirmation may help the plan reconcile the record.
What to do: ask the provider for the authorization request and any confirmation of submission. If it exists, attach it. Denials that rest on a factual error about the record are among the more straightforward to overturn.
Out-of-network
The provider is not contracted with your plan, so the claim is denied or paid at a much lower rate — and you may be billed the difference.
Federal surprise-billing protections cover important situations here, including emergency care and certain out-of-network care delivered at an in-network facility. If you went to an in-network hospital and an out-of-network anesthesiologist or radiologist was part of your care without your choosing them, that is precisely the scenario those protections address.
What to do: establish whether you chose the out-of-network provider. If you did not — emergency, or an ancillary provider assigned to you at an in-network facility — say so explicitly in writing. Also appeal on network adequacy grounds if no in-network option was reasonably available for the service you needed.
Experimental or investigational
The plan classifies the treatment as unproven. These are the hardest denials to reverse through internal appeal, because the plan is applying a policy position rather than evaluating your specific facts.
What to check: HealthCare.gov identifies medical-judgment and experimental or investigational denials as possible external-review categories. Eligibility and the binding effect depend on the applicable process, so follow the final denial notice and ask what evidence the reviewer accepts.
Timely filing
The claim was recorded as arriving after a filing deadline. The plan and provider records are needed to determine who submitted it, which deadline applied, and whether the patient can be billed.
What to check: ask for the receipt date and cited plan term, then ask the provider and plan in writing how member responsibility is determined for that claim.
The step almost nobody takes
An appeal outcome cannot be predicted from the denial category alone. A complete submission can identify the decision being challenged, the plan term or criterion at issue, and the records the claimant wants reviewed.
Before you write anything, confirm two things: the deadline on your notice, and whether your plan is fully insured or self-funded. Funding status helps narrow the process but does not by itself determine the filing destination, deadline, or law governing a particular claim.