How Insurance Denials and Appeals Work

Few experiences in healthcare are as frustrating as receiving a denial letter. Your doctor recommended a treatment. You received the care. Now your insurance says they won't pay, leaving you with potentially thousands of dollars in bills. The denial letter offers vague reasons and bureaucratic language that doesn't help you understand what went wrong.

Insurance denials affect millions of claims annually. Kaiser Family Foundation research found that approximately 17% of in-network claims are denied across Marketplace plans, while a ProPublica analysis revealed that some individual plans deny more than 25% of claims. Some denials are legitimate enforcement of coverage rules. Others are errors or questionable interpretations. The appeals process exists to challenge denials, and many appeals succeed, but most people don't appeal because they don't know how. This article is informed by publicly available CMS Marketplace data, KFF claim denial analyses, state insurance department records, and ACA regulatory requirements.

This article explains how denials happen, what the appeals process involves, and why persistence often pays off.

What Insurance Denials Are Meant to Do

Denials enforce the boundaries of what insurance covers. Your policy doesn't cover everything; it covers specific benefits under specific conditions. Denials occur when claims fall outside those boundaries — or at least when the insurer believes they do.

From the insurer's perspective, denials prevent inappropriate utilization. Paying for everything without review would increase costs and premiums. Denials are a cost control mechanism, ensuring that payment flows only to covered, appropriate care.

The appeals process provides recourse when denials are wrong. Recognizing that automated systems and human reviewers make mistakes, regulators require insurers to offer appeals. The appeals system is meant to correct errors and provide due process. Under ACA Section 2719, all non-grandfathered health plans must provide both internal appeal and external review processes for adverse benefit determinations.

How Insurance Denials and Appeals Actually Work in Practice

Denial triggers: Claims can be denied for many reasons. Common causes include: services not covered under your plan, services deemed not medically necessary, missing prior authorization, coding or billing errors, out-of-network providers without out-of-network benefits, and exhausted benefit limits. Data from HealthCare.gov plans shows denial rates ranging from 12% to 20% depending on the insurer and plan type.

Initial denial notice: When a claim is denied, you receive an Explanation of Benefits showing the denial and a stated reason. The reason is often a code or brief phrase that may not clearly explain the problem. Federal law requires specific denial information, including the clinical rationale if medical necessity was the basis for the denial, but implementation varies in practice.

Internal appeal: The first appeal level is internal, reviewed by the insurer. You submit a request explaining why the denial was wrong, often with supporting documentation from your provider. A different reviewer examines the case. Internal appeals must usually be filed within 180 days. The insurer must complete its internal review within 30 days for non-urgent cases and 72 hours for urgent cases.

External review: If the internal appeal fails, you can request external review by an independent third party. External reviewers aren't employed by the insurer and can overturn denials. This level is particularly valuable for medical necessity denials, where an independent medical opinion may differ from the insurer's. When patients do pursue external review, studies indicate they win approximately 40% to 50% of the time, a success rate that underscores how often initial denials are overturned.

Expedited appeals: When delays could seriously harm your health, expedited appeals provide faster decisions. These are available for urgent situations where waiting for standard timelines would be dangerous.

Why Insurance Denials Feel Unfair or Arbitrary

Denial rates are high. Across HealthCare.gov Marketplace plans, denial rates of 12% to 20% of claims are common. While many denials are resolved through corrections and resubmission, the volume creates a sense that insurers deny first and ask questions later.

Denial reasons are often unclear. "Not medically necessary" doesn't tell you what information was missing or what standard wasn't met. This vagueness makes it hard to know how to respond. Clearer explanations would help but aren't always provided.

The process advantages insurers. Of the approximately 17% of in-network claims that are denied, only about 0.2% are appealed by patients, according to KFF data. Insurers face little cost from denying claims that won't be appealed. This dynamic creates incentives for aggressive denial practices, because the overwhelming majority of denials are simply accepted.

Appeals require expertise and persistence. Successfully appealing often requires understanding how to write appeal letters, obtaining supporting documentation from providers, and knowing the relevant regulations. This expertise is unevenly distributed, disadvantaging those without resources or knowledge.

Timing adds stress. Appeals have deadlines. Denials often arrive when you're already dealing with health issues. The administrative burden of appealing compounds the stress of illness.

What People Misunderstand About Insurance Denials and Appeals

Most appeals are not filed. Only about 0.2% of denied claims are appealed by patients. Yet studies show that appeals frequently succeed, especially external reviews where patients win 40% to 50% of the time. The first denial is often not the final word.

Your doctor can help. Providers often assist with appeals, writing letters of medical necessity or providing documentation. Their involvement significantly strengthens appeals. Don't assume you must navigate the process alone.

Persistence matters. Denials that seem final can often be overturned with additional information or escalation. Multiple appeal levels exist specifically because initial reviews may be wrong. Giving up too early forfeits legitimate claims.

State regulators can intervene. If internal and external appeals fail, state insurance commissioners handle complaints. The National Association of Insurance Commissioners (NAIC) maintains consumer complaint databases, and regulatory complaints sometimes resolve issues that the normal appeals process didn't. This isn't always effective, but it's another avenue.

System Incentives Explained

To understand why denial rates are as high as they are, it helps to examine the economic incentives within the insurance system and the regulatory structures designed to counterbalance them.

The economics of denial. Insurance companies operate on the difference between premium revenue collected and claims paid out, a figure known as the medical loss ratio. The ACA requires that large-group insurers spend at least 85% of premium revenue on medical claims and quality improvement, and individual and small-group insurers must spend at least 80%. This means insurers have a defined margin to work within. Denying claims, even a small additional percentage, can meaningfully improve an insurer's financial performance within these constraints. When the vast majority of denied claims are never appealed, the financial calculus favors denying borderline claims.

Automated adjudication and denial volume. Most claims are processed through automated adjudication systems that apply pre-programmed rules. These systems flag claims for denial based on coding mismatches, missing prior authorizations, or criteria thresholds. The automation means that denials can be issued at high volume with minimal cost to the insurer, while appeals require individual human review, which is resource-intensive. This asymmetry means it costs insurers very little to deny and considerably more to review appeals, creating a structural imbalance.

Regulatory oversight and its limitations. Federal and state regulators require insurers to maintain appeal processes, report denial rates, and comply with timely decision-making standards. CMS publishes Marketplace plan denial and appeal data, and state insurance departments accept consumer complaints. However, enforcement varies significantly by state. Some states actively investigate denial patterns and impose penalties; others are resource-constrained and primarily reactive. The regulatory framework provides a floor of consumer protections but does not eliminate the incentive to deny.

The role of external review. External review, where an independent physician or review organization evaluates the denial, serves as the most important check on insurer denial practices. Because external reviewers are not employed by or financially dependent on the insurer, they provide a genuinely independent evaluation. The 40% to 50% overturn rate at external review suggests that a substantial portion of denied claims were inappropriately denied at the internal level. This mechanism is only effective, however, when patients actually use it, which very few do.

Real-World Example: Denied Claim for an Out-of-Network Specialist

Consider a patient named Linda who has been experiencing chronic migraines. Her primary care doctor refers her to a neurologist. Linda checks her insurer's online provider directory, finds a neurologist listed as in-network, and schedules an appointment. She sees the neurologist, receives treatment, and expects a routine in-network claim. Instead, six weeks later, she receives an EOB showing the claim was denied as out-of-network, leaving her responsible for a $2,800 bill.

What happened. Linda's insurer updated their provider network between the time she checked the directory and the date of her appointment. The neurologist's contract with the insurer had ended, but the online directory had not been updated to reflect the change. From the insurer's automated system perspective, the claim was correctly denied: the provider was out-of-network on the date of service. From Linda's perspective, she relied on the insurer's own directory and did everything right.

First-level internal appeal. Linda files an internal appeal within the 180-day deadline. In her appeal letter, she includes a screenshot of the provider directory showing the neurologist listed as in-network (she had taken a screenshot before the appointment as a precaution), the date she checked the directory, and her referral from her primary care doctor. She argues that she relied in good faith on the insurer's published directory and should not be penalized for a directory error. The insurer's first-level reviewer upholds the denial, stating that the provider was not in-network on the date of service regardless of the directory listing.

Second-level internal appeal with network adequacy argument. Linda files a second-level appeal, this time adding a network adequacy argument. She documents that within her insurer's network, there were no neurologists accepting new patients within 30 miles of her home at the time she needed the appointment. She references her state's network adequacy standards, which require insurers to maintain sufficient specialist availability within geographic and timely access standards. She also cites federal regulations requiring insurers to hold patients harmless when provider directories contain inaccurate information. A different reviewer examines the case but again upholds the denial.

External review through the state insurance department. Linda requests an external review, which is conducted by an independent review organization contracted by her state's insurance department. The external reviewer examines the directory evidence, the network adequacy data, and the applicable state and federal regulations. The external reviewer overturns the denial, finding that Linda relied on the insurer's own published information and that the insurer failed to maintain an accurate directory. The insurer is required to reprocess the claim at in-network rates. Linda's final responsibility is a $40 specialist copay instead of $2,800.

Linda's case illustrates several key points: directory errors are a real and recurring source of out-of-network denials; internal appeals may uphold denials even when the evidence favors the patient; and external review provides a genuinely independent check that frequently overturns inappropriate denials. It also illustrates why documentation, including screenshots and records of provider directory searches, is essential.

How to Navigate This System More Effectively

Tip: When you receive a denial, request the full explanation in writing, including the specific plan provision or clinical criteria that was not met. Vague denial language like "not medically necessary" is not sufficient under federal law. Knowing the exact basis for the denial allows you to target your appeal.

Tip: Always appeal. The data is clear: the vast majority of patients who receive denials never appeal, yet those who do frequently succeed. Even if you are uncertain about the outcome, filing an appeal costs you nothing beyond time and may save you hundreds or thousands of dollars.

Tip: Ask your treating physician to write a letter of medical necessity supporting your appeal. Appeals that include clinical documentation from the treating provider are significantly stronger than patient-only appeals. Many physicians and their staff are experienced in writing these letters and will do so upon request.

Tip: If your internal appeal is denied, exercise your right to external review. External reviewers overturn insurer denials 40% to 50% of the time. This is your strongest recourse and the most independent evaluation available.

Tip: Document everything. Take screenshots of provider directories before appointments. Keep copies of referral letters, prior authorization approvals, and all correspondence with your insurer. This documentation is the foundation of a successful appeal.

Tip: If you believe your insurer is acting in bad faith or violating regulations, file a complaint with your state insurance department. Regulatory complaints create a record that may trigger investigation and can sometimes resolve individual cases that the appeals process did not.

Insurance denials are a significant feature of the American healthcare system. They serve legitimate purposes but also create barriers to care and payment. The appeals process offers recourse but requires knowledge and persistence that many patients lack. Understanding how denials work and that appeals often succeed empowers patients to challenge inappropriate denials rather than simply accepting them.

Sources and Further Reading

Kaiser Family Foundation — "Claims Denials and Appeals in ACA Marketplace Plans" (kff.org)
CMS Marketplace Plan Denial and Appeals Data — Centers for Medicare & Medicaid Services (cms.gov)
State Insurance Department Appeal and Complaint Statistics — National Association of Insurance Commissioners (naic.org)
ProPublica — Analysis of health plan claim denial rates (propublica.org)
ACA Section 2719 — Internal Claims and Appeals and External Review Processes (law.cornell.edu)
NAIC Consumer Complaint Data — National Association of Insurance Commissioners (naic.org)