Few things are more frustrating than dealing with a health insurance claim rejection after you have already received medical care. You followed the process, you have coverage, and yet the bill still lands in your lap. For millions of Americans, this is not a rare occurrence. It is an everyday reality.
According to a KFF analysis of ACA Marketplace plans, insurers denied approximately 17% of in-network claims in 2021. That number likely understates the full picture because it only reflects plans subject to federal reporting requirements.
Understanding why claims get denied is the first step toward preventing it from happening to you, and knowing your rights is what helps you win when it does. This guide covers every major reason health insurance claims are rejected, what each denial really means, and the concrete steps you can take to appeal, resubmit, or avoid the problem entirely.
1. The Service Was Not Medically Necessary
This is the single most common reason health insurance claims are denied. Insurers use their own clinical guidelines to determine whether a treatment, test, or procedure meets their definition of “medically necessary.” If your insurer decides the service does not meet that threshold, the claim is rejected regardless of what your doctor recommends.
What “Medically Necessary” Actually Means to Insurers
Every insurance company has its own rules, and those rules don’t necessarily match up with what is considered normal medical practice or what your doctor thinks is best for you. Your insurance company may call a treatment that your doctor thinks is necessary “elective,” “experimental,” or “outside their accepted protocols.”
Some of the most common services that fall under this category are advanced imaging (such MRIs or CT scans), some procedures, long-term physical therapy, and mental health care that lasts more than a few sessions.
What You Can Do
Request a written explanation of the denial and the specific clinical guidelines used. Your doctor can then write a Letter of Medical Necessity on your behalf that directly addresses the insurer’s criteria. This letter, combined with a formal appeal, overturns a meaningful share of medical necessity denials. Do not accept the first rejection as final.
2. The Provider Was Out of Network
When you see a doctor, go to a hospital, or consult a specialist who’s not part of your insurance plan’s network, your insurer might reject the claim completely. Alternatively, they could only reimburse a fraction of the cost.
The Surprise Billing Problem
Even when you go to an in-network hospital, certain providers working within that facility, such as an anesthesiologist, radiologist, or assistant surgeon, may be out of network. The No Surprises Act, which took effect in January 2022, now provides federal protections against surprise out-of-network billing for emergency care and certain non-emergency services, but the rules are complex and not every scenario is covered.
How to Protect Yourself
Before any non-emergency procedure, confirm that every provider involved is in your network. Do not rely solely on the hospital’s word. Call your insurer directly, give them the name and NPI number of each provider, and get confirmation in writing or by logging the call reference number. If you are in a situation where an out-of-network claim has already been denied, check whether the No Surprises Act protections apply to your case.
3. Lack of Prior Authorization
A lot of health insurance plans insist on getting the green light before they’ll cover specific surgeries, medications, or visits to specialists. This process is called prior authorization, or pre-authorization. If you or your doctor skip this step, the insurance company can refuse to pay the claim entirely, even if the service would have been covered if approved.
Services That Commonly Require Prior Authorization
Prior authorization requirements vary by plan, but frequently apply to:
Elective surgeries and inpatient hospital stays. Brand-name prescription drugs, particularly specialty medications. Certain diagnostic imaging procedures such as MRIs and PET scans. Mental health and substance use disorder treatment beyond a set number of sessions. Durable medical equipment and home health services.
How to Avoid This Denial
Always ask your doctor’s office whether prior authorization is required before scheduling a procedure. Most provider offices handle this routinely, but ultimately the responsibility falls on the patient if authorization is not obtained. If your claim was denied for lack of prior authorization after the fact, a retroactive authorization request is sometimes possible, especially if an emergency was involved or if the provider failed to notify you.
4. Coverage Had Lapsed or the Policy Was Not Active
A claim submitted during a period when your coverage was not active will be denied. This can happen for several reasons. A missed premium payment can trigger a lapse. A change in employment can end your employer-sponsored coverage sooner than expected. An administrative error during an enrollment or renewal period can result in a gap you were not aware of.
COBRA Timing Errors
Many people who lose employer coverage intend to use COBRA continuation coverage but miss the 60-day election window or the subsequent premium payment deadlines. COBRA coverage can also be retroactively elected, but the premiums for all retroactive months must be paid at once. If a claim lands in a period where COBRA was not yet elected or premiums were overdue, it will be rejected.
What to Do
First, get in touch with your insurer right away. Have your proof of enrollment and payment ready. If the lapse in coverage was due to a mistake by your employer or the insurer, you’ll need to file a formal complaint and appeal the decision. It’s also important to understand your state’s laws. Most states have a grace period before they can cancel your coverage for not paying.
Want to avoid costly claim mistakes? Explore our complete Health Insurance Guide: Plans, Costs, and How to Choose the Right Coverage.
5. The Claim Contains Errors or Incorrect Billing Codes
Medical billing is extraordinarily complex, and even minor errors in a claim submission can trigger a denial. These errors are more common than most patients realize and are frequently the fault of the provider’s billing department rather than the patient.
Common Billing Errors That Cause Rejections
Incorrect or mismatched patient information, such as a name spelled differently from what is on file with the insurer. Wrong diagnosis codes (ICD-10 codes) or procedure codes (CPT codes). Duplicate claims submitted for the same service. Services billed under the wrong provider NPI number. Coordination of benefits errors when a patient has more than one insurance plan.
How to Handle This
Ask your provider for a detailed bill and then compare it to the Explanation of Benefits (EOB) statement you got from your insurance company. If you see a mistake, tell the provider’s billing department to fix it and send the claim again. At this level, most coding mistakes can be fixed without a formal appeal. Keep track of all your communications, including dates, names, and reference numbers.
6. The Treatment Is Considered Experimental or Investigational
Insurance companies maintain records of procedures and medications classified as experimental or investigational. These are treatments that haven’t yet become standard practice or haven’t been approved by the FDA for the specific condition at hand. Even if your doctor thinks the treatment is the right call, the insurer can still refuse to cover it.
Why This Matters for Cancer and Rare Disease Patients
Experimental treatment denials hit hardest among patients with cancer, rare diseases, or conditions where standard treatments have failed. Clinical trials and cutting-edge therapies are precisely the situations where these denials occur most frequently.
Your Options
Some states have laws requiring insurers to cover routine patient costs associated with clinical trials. Federal law under the ACA also requires Marketplace plans to cover routine costs for individuals in approved clinical trials. If your treatment has been denied as experimental, review whether these protections apply to your situation. An appeal backed by peer-reviewed literature and a specialist’s recommendation can also succeed.
7. The Claim Was Filed After the Deadline
Every health insurance plan sets a deadline by which claims must be submitted after services are rendered. These timelines vary from 90 days to one year depending on the plan. If your provider submits the claim after that window closes, it will be rejected for being untimely, regardless of whether the service itself was covered.
This issue almost always originates with the provider’s billing department, but the financial fallout lands on the patient. It is worth asking your provider when claims are typically submitted and following up if you have not received an EOB from your insurer within a reasonable time after receiving care.
8. A Pre-Existing Condition Exclusion Was Applied
While the ACA eliminated pre-existing condition exclusions for most health insurance plans, these exclusions still exist in certain types of coverage. Short-term health plans, grandfathered health plans, and other employer self-funded plans that don’t have to follow ACA rules can still deny claims for problems that were already there before your coverage started.
If you have one of these types of plans and your claim was refused because of a pre-existing condition, the main question is whether your plan is allowed by law to do that. You can get guidance from a registered health insurance professional to look over your coverage and your rights.
9. Coordination of Benefits Issues With Multiple Plans
If you have more than one health insurance plan, such one from your own job and one from your spouse’s job, the two insurers need to work together to figure out which plan pays first and which one pays second. Claims can be refused if the coordination of benefits (COB) process fails or if one insurance company doesn’t know about the other coverage.
Insurers often send coordination of benefits questionnaires and require responses within a specific timeframe. Ignoring these requests can trigger denials until the information is updated.
10. Mental Health and Substance Use Claims Face Unique Barriers
Even with the Mental Health Parity and Addiction Equity Act (MHPAEA) in place, which mandates that insurers treat mental health and substance use disorder services the same as physical health services, denials in this area are still a problem. Insurers continue to deny claims for inpatient psychiatric care, residential treatment, and extended outpatient therapy, often citing medical necessity.
A 2019 federal court ruling in Wit v. United Behavioral Health found that United’s criteria for coverage of mental health treatment were illegally more restrictive than its criteria for medical and surgical treatment. This case set a landmark precedent, but enforcement remains inconsistent.
If you receive a mental health claim denial, the parity protections under MHPAEA give you specific grounds for appeal that go beyond a standard medical necessity argument.
How to Appeal a Denied Health Insurance Claim
Knowing why your claim was denied is only half the battle. Here is a straightforward process for fighting back.
Step 1: Understand Your Denial Letter
Every denial must include the specific reason for rejection and the clinical criteria or plan provisions used. Read it carefully. The language used in the denial letter will guide your appeal strategy.
Step 2: File an Internal Appeal
You have the right to appeal any denied claim directly with your insurer. For plans subject to ACA rules, insurers must respond to urgent care appeals within 72 hours and standard appeals within 30 days. Submit your appeal in writing, include supporting documentation from your doctor, and reference the specific plan provisions that support your position.
Step 3: Request an External Review
If your internal appeal is denied, you can request an independent external review. An external reviewer is a third party with no financial relationship to your insurer. For most plans, their decision is binding on the insurer. External review requests must typically be filed within four months of the final internal denial.
Step 4: File a Complaint With Your State Insurance Department
Your state’s Department of Insurance is a powerful ally. Filing a complaint puts the insurer on notice that a regulator is watching and often accelerates resolution. States also have consumer assistance programs that can help you navigate the process.
Frequently Asked Questions (FAQ)
Health insurance companies deny claims for a wide range of reasons, including services not meeting their definition of medical necessity, lack of prior authorization, out-of-network providers, billing errors, coverage lapses, and treatments classified as experimental. Each denial is specific to the plan’s terms and the circumstances of the service.
Yes. You have a legal right to appeal any denied claim. Most plans subject to ACA rules must allow an internal appeal and then an independent external review. The process varies by plan, but starting with a written internal appeal supported by documentation from your doctor is always the right first step.
Timelines vary by plan, but under ACA rules you generally have at least 180 days from the date of the denial notice to file an internal appeal. For external review requests, the window is typically four months from the final internal denial. Check your denial letter and plan documents for your specific deadlines.
Prior authorization is advance approval from your insurer that a specific treatment or medication is covered under your plan before you receive it. If your provider proceeds without obtaining this approval, the insurer can deny the resulting claim. Always confirm with your provider whether a service requires prior authorization before it is scheduled.
Not necessarily. A denial is the start of a process, not the end of it. Many denied claims are overturned on appeal, especially those denied on medical necessity grounds. Exhaust your internal and external appeal options before accepting personal financial responsibility for the full cost.
An Explanation of Benefits (EOB) is a statement from your insurer showing how a claim was processed, what was covered, what was denied, and why. It is not a bill, but it is an essential document for understanding a denial and building your appeal. Always request an EOB for any denied claim.
Research and legal proceedings have found that mental health and substance use disorder claims are denied at higher rates than comparable medical and surgical claims, despite federal parity laws. If your mental health claim is denied, the Mental Health Parity and Addiction Equity Act gives you specific grounds to challenge the denial.
If your doctor’s office fails to obtain required prior authorization and the claim is denied, you can ask the provider to seek a retroactive authorization or correct the situation with the insurer. In many cases, the financial responsibility for the error lies with the provider, not the patient. Review your plan documents and consult a health insurance specialist for guidance specific to your situation.
The Bottom Line: Denials Are Common, But They Are Not Inevitable
Health insurance claim rejections are frustrating, but they are rarely the end of the road. Most denials stem from preventable issues, whether it is a missed prior authorization, a billing code error, or an out-of-network provider that could have been avoided with a quick verification call. For the denials that do happen, the appeals process is a genuine avenue for resolution, not just a formality.
The single most effective way to protect yourself is to understand your plan before you need it and work with a knowledgeable professional who can help you navigate coverage questions before they become claim problems.
Get the Right Coverage and Avoid Claim Surprises
At Keen Coverage, our licensed health insurance specialists help individuals, families, and small business owners choose plans with clear, understandable coverage. We walk you through exactly what is and is not covered, flag common prior authorization requirements, and make sure you are enrolled in a plan that fits your actual healthcare needs, not just your budget.
Don’t let claim rejections catch you off guard, read our in-depth Health Insurance Guide to compare plans, understand costs, and choose the right coverage with confidence.