Why Claim Denials Happen More Than You'd Expect
A denied health insurance claim can feel like a gut punch, especially when you're already dealing with a medical issue. But denials are far more common than most policyholders realize, and a significant share of them are overturned on appeal. Understanding the specific reasons insurers reject claims puts you in a much stronger position to fight back — or to prevent the problem in the first place.
This article breaks down the most frequent causes of claim rejections in plain terms, explains why they happen, and walks through what you can actually do about each one. It is general educational information, not personalized insurance or legal advice — your specific situation will depend on your plan documents and your state's regulations.
Receiving care from an out-of-network provider without realizing it.
Why it happens: Patients often assume that because a hospital is in-network, every doctor treating them there is too. In reality, anesthesiologists, radiologists, and emergency physicians frequently contract independently and may be out-of-network.
Missing or skipping required prior authorization before a procedure.
Why it happens: Patients often don't know that certain services — imaging, specialist visits, surgeries — require insurer approval in advance. Providers sometimes neglect to obtain it, or obtain it for the wrong procedure code.
Submitting a claim with incorrect or mismatched billing codes.
Why it happens: Medical billing uses standardized codes (CPT, ICD-10) to describe diagnoses and procedures. A single digit error — a transposed number or a code that doesn't match the stated diagnosis — will typically trigger an automatic denial.
Letting appeal deadlines pass without filing.
Why it happens: After a stressful medical event, paperwork often gets set aside. Many policyholders don't realize that internal appeal deadlines are typically 180 days from the denial date — and missing that window can permanently waive your right to appeal.
Failing to provide adequate documentation of medical necessity.
Why it happens: Insurers deny claims when they determine a service was not medically necessary — often because the clinical documentation submitted doesn't clearly support it. Providers may use shorthand notes that meet clinical standards but don't satisfy insurer criteria.
Assuming a denial is final and taking no further action.
Why it happens: The denial letter can feel authoritative and discouraging. Many policyholders accept it as the final word, not realizing that a large percentage of appeals — especially those supported by physician letters — are decided in the patient's favor.
Your Right to Appeal — and How to Use It
Federal law under the Affordable Care Act gives you the right to appeal most claim denials from non-grandfathered health plans. There are two levels: an internal appeal handled by your insurer, and an external review conducted by an independent organization if the internal appeal fails.
17%
ACA marketplace claims denied on average
A KFF analysis of 2021 data found that ACA marketplace insurers denied roughly 17% of in-network claims, though rates varied widely by insurer.
<1%
Denied claims that are actually appealed
The same KFF analysis found that consumers formally appealed less than 1% of denied claims, leaving many potentially valid claims unpursued.
When you receive a denial notice — called an Explanation of Benefits (EOB) — read it carefully. The EOB must state the specific reason for the denial and explain how to file an appeal. Gather supporting documentation: the original claim, your EOB, medical records related to the service, and a letter from your treating provider explaining why the care was medically necessary. Submit everything in writing and keep copies.
For prior authorization issues specifically, see our explainers on how prior authorization works and what to do when it's denied. For a broader look at claim-time surprises, these common situations that catch policyholders off guard are worth reviewing before your next claim.
Appeal Deadlines Are Strict — Don't Wait
Under federal rules, you generally have 180 days from the date on your denial notice to file an internal appeal. Missing this deadline can eliminate your right to challenge the decision entirely. Read every denial notice promptly, note the deadline, and begin gathering your documentation immediately — even if the process feels overwhelming.
This article is for general informational and educational purposes only. It is not personalized insurance, financial, or legal advice. Coverage, appeal rights, and deadlines vary by plan and state. Always read your actual policy documents and consult a licensed insurance professional or patient advocate for guidance specific to your situation.
