Insurance Claim Denied — What It Means and What to Do

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.

Common reasons for claim denial

Most denials fall into a handful of categories: the service was judged not medically necessary, prior authorization was missing, the provider was out-of-network, the service was not covered under your plan, or the claim contained a coding or information error. Each reason points to a different appeal strategy, and the exact reason code on your denial letter is the starting point.

Insurance denial reasons explained → — a plain-English breakdown of the most common denial codes and what each one means for your appeal. If your denial cites medical necessity specifically, see what a medical necessity denial means and how to appeal it.

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.

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.

The appeals process — in brief

In outline, appealing a denial means: understand the exact denial reason, contact your provider (who can often resubmit with corrected coding or documentation), gather supporting evidence such as a letter of medical necessity, file the internal appeal in writing before your plan's deadline, and — if that is denied — request an independent external review, whose decision is generally binding.

How to appeal an insurance denial → — the full step-by-step process, including what to include in your appeal letter, the timeframes insurers must meet, and how external review works.

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.

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.

Summary

A denied insurance claim is not a final determination of what you owe. Most denials can be appealed, and a meaningful proportion of appeals succeed. The denial reason — found on your EOB and denial letter — is the starting point for deciding how to proceed.

For technical errors like incorrect billing codes or missing member information, the provider can often resubmit the claim without a formal appeal. For denials based on medical necessity or prior authorization, an appeal supported by clinical documentation from your treating physician is the most effective approach.

If an internal appeal is unsuccessful, external review by an independent party is available under federal law — and the external reviewer's decision is binding on your insurer. Understanding your rights and the process gives you a clear basis for deciding whether and how to pursue the appeal.