A denial is not the end
When a health insurance claim is denied, your Explanation of Benefits (EOB) will show $0 covered and the full billed amount listed under "not covered" or "your responsibility." That figure can be alarming — particularly after a significant medical event.
But a denial is not a final determination of what you owe. Federal law gives you the right to appeal most insurance denials, and appeals are often successful. Studies of the ACA marketplace have found that policyholders who appeal denials win a significant portion of cases — particularly at the external review stage.
The first step is understanding why the claim was denied. The denial reason determines the most effective path forward.
Your Explanation of Benefits is the primary document for understanding a denial. It includes a reason code and, in many cases, a plain-language explanation. If you do not have your EOB, request one from your insurer's member services line or check your online member portal.
Common reasons for claim denial
| Denial reason | What it typically means | Fixable? |
|---|---|---|
| Not medically necessary | The insurer determined the service did not meet its clinical criteria for medical necessity. | Often — with supporting documentation from your provider. |
| Prior authorization not obtained | The service required advance approval from the insurer that was not requested or granted. | Sometimes — if the authorization was obtained but not recorded, or if the denial can be appealed on clinical grounds. |
| Out-of-network provider | The provider was not in your insurance plan's network and your plan does not cover out-of-network services, or covers them at a lower rate. | Partially — particularly if the out-of-network use was unavoidable (emergency, no in-network alternatives). |
| Service not covered | The procedure or service is explicitly excluded from your plan. | Depends on the plan and the service. Worth confirming with your plan documents. |
| Incorrect billing code | The procedure code submitted did not match the diagnosis code, or was entered incorrectly. | Yes — the provider can resubmit with the corrected code. |
| Claim filed after deadline | The claim was submitted outside the insurer's filing window. | Sometimes — if the delay was due to insurer error or circumstances outside your control. |
| Duplicate claim | The claim appears to be a second submission for a service already processed. | Yes — if it was filed in error or the original was not processed correctly. |
| Member information error | The wrong member ID, date of birth, or plan number was used on the claim. | Yes — the provider can resubmit with corrected information. |
How to read your denial letter
Your insurer is required to provide a written explanation of any denial. This explanation — typically included with your EOB or sent as a separate letter — should include:
- The specific reason for the denial, in plain language
- The plan provision, exclusion, or guideline the denial is based on
- Instructions for how to appeal
- The deadline to file an appeal
- Information about your right to external review
If any of these elements are missing from your denial letter, contact your insurer's member services and ask for a complete explanation in writing. You are entitled to know specifically why the claim was denied and what your appeal rights are.
Federal law requires insurers to allow at least 180 days to file an internal appeal, but your plan's deadline may be shorter. Write down the deadline as soon as you receive the denial — missing it can eliminate your appeal rights.
Before filing an appeal, check these three things
Many denials are resolved before a formal appeal is ever filed — because the underlying issue is a fixable error rather than a genuine coverage dispute. Before you go through the appeals process, it is worth spending a few minutes on the following.
1. Was the claim coded correctly?
A significant proportion of denials are caused by incorrect procedure or diagnosis codes on the original claim submission. A single transposed digit or an outdated code can trigger an automatic denial — even for a service your plan clearly covers. Contact the billing department and ask them to confirm that the CPT and ICD codes on the submitted claim match the services you received. If there is a coding error, the provider can resubmit the corrected claim and the insurer will reprocess it — often without a formal appeal. See Common Medical Billing Errors for a full breakdown of the types of coding issues that appear most frequently.
2. Does your EOB match the provider bill?
Your Explanation of Benefits shows how your insurer processed the claim — what was covered, what was adjusted, and what the insurer determined to be your patient responsibility. If the amount your provider is billing you is significantly higher than the "patient responsibility" figure on your EOB, the discrepancy may be a billing error rather than a coverage denial. Compare the two documents line by line before assuming you owe the full amount. What Is an EOB (Explanation of Benefits)? explains what each section of the EOB means and how to read it alongside a provider bill.
3. Was the denial caused by missing information?
Denials for "missing information," "insufficient documentation," or "claim incomplete" are among the most straightforward to resolve — because the fix is simply supplying what was missing. This could be prior authorization documentation, a referral, a letter of medical necessity from your physician, or updated insurance details. Ask the billing department what specific information is needed and whether the claim can be resubmitted once it is provided. If you are not sure where to start, requesting a full itemized bill first gives you the detail needed to understand exactly what was submitted — and what may be missing. See How to Request an Itemized Medical Bill.
If any of the three issues above apply to your situation, ask the provider to correct and resubmit the claim first. A corrected resubmission is faster than a formal appeal and avoids the appeals process entirely if the underlying issue is administrative rather than a genuine coverage dispute.
The appeals process — step by step
Understand the denial reason
Read your EOB and denial letter carefully. Identify the specific reason code and the plain-language explanation. The denial reason determines what evidence or documentation you need to gather for an appeal.
Contact your provider
Call the billing department or your doctor's office and let them know the claim was denied. For denials related to billing codes, medical necessity, or prior authorization, your provider may be able to resubmit the claim with corrected information or additional documentation — which can resolve the issue without a formal appeal.
Gather supporting documentation
Depending on the denial reason, your appeal may need to include: a letter of medical necessity from your treating physician, your medical records related to the service, prior authorization documentation if obtained, and a copy of your plan's coverage documents showing the relevant provision. The more specific your documentation, the stronger your appeal.
File the internal appeal
Submit your appeal to your insurer in writing, following the instructions in your denial letter. Include your account information, the claim number, a clear statement of why you believe the denial was incorrect, and your supporting documentation. Keep a copy of everything you submit.
Wait for the internal appeal decision
Insurers are required to decide internal appeals within specific timeframes: 30 days for pre-service appeals (services not yet received), 60 days for post-service appeals (services already received), and 72 hours for urgent care appeals. The decision must be provided to you in writing.
Request an external review if the internal appeal is denied
If your internal appeal is denied, you have the right to an independent external review. An external reviewer is not affiliated with your insurer and their decision is generally binding. Under federal law, you typically have 4 months after the internal appeal decision to request external review. Your denial letter must include instructions for how to request one.
Special situations
Emergency care denials
The No Surprises Act provides specific protections against surprise billing for emergency care, including care from out-of-network providers in emergencies. If your insurer denied a claim for emergency services on the grounds that the provider was out of network, the denial may not be consistent with federal law. Contact your insurer's member services and reference the No Surprises Act.
Mental health and substance use denials
The Mental Health Parity and Addiction Equity Act requires health plans to cover mental health and substance use disorder services on terms that are no more restrictive than coverage for comparable medical and surgical services. If your mental health or substance use claim was denied on the basis of medical necessity or coverage limitations, it may be worth examining whether the denial is consistent with parity requirements.
Experimental or investigational treatment denials
Some plans deny claims for treatments deemed experimental or investigational. If you have a serious medical condition and your doctor recommended the treatment, a detailed letter of medical necessity — including published clinical evidence supporting the treatment — can be central to an appeal.
Data from state insurance commissioners and federal marketplace reports consistently show that a meaningful proportion of internal and external appeals result in the original denial being reversed. Filing an appeal — even if it takes effort — is often worthwhile, particularly for larger claims.
If you cannot pay while the appeal is in progress
You generally do not need to pay the disputed portion of a bill while an appeal is pending. Contact both your provider's billing department and your insurer to notify them that an appeal is in progress and ask that collection activity be paused. Most providers will accommodate a reasonable hold during a legitimate appeal process. Get confirmation of any hold in writing.
If a bill has already been sent to collections while an appeal is in progress, contact the collections agency in writing, inform them of the pending appeal, and request that collection activity be suspended. Also notify your insurer and provider.