What percentage of health insurance claims are denied?

Industry data suggests commercial insurers deny roughly 10–20% of in-network claims on first submission, though rates vary by plan and service type. Prior authorization denials for specialty drugs and advanced imaging run higher — 25–40% for some GLP-1 medications and MRIs. A significant share of first-pass denials are overturned on appeal when patients submit complete clinical documentation.

Do insurance companies deny claims to save money?

Insurers operate under utilization management programs designed to control costs — prior authorization, step therapy, and medical necessity review all serve that function. A denial is not always a final coverage decision; it often means the claim did not meet documentation or authorization requirements at submission. Federal law under ERISA §503 and ACA §2719 requires insurers to provide a formal appeal process for denied claims.

What is the most common reason for claim denial?

Missing or expired prior authorization (remark code CO-197) is the single most common claim denial reason for imaging, surgery, specialty drugs, and durable medical equipment. Medical necessity denials (CO-50) are the second most common, especially for MRIs, CT scans, physical therapy beyond visit limits, and specialty medications. Coding errors (CO-4, CO-11) account for a large share of administrative denials that can sometimes be fixed with a corrected claim.

Can a denied claim be appealed?

Yes. Federal law guarantees your right to appeal denied claims. ERISA §503 covers employer-sponsored plans with up to 180 days to file an internal appeal. ACA §2719 covers marketplace plans with 60-day appeal windows in most states. After internal denial, you can request external review by an independent reviewer. Appeals with complete clinical packets succeed roughly 40–55% on first submission.

How long do I have to appeal a denied health insurance claim?

Deadlines vary by plan type: ERISA employer plans typically allow 180 days from the denial date. ACA marketplace plans: 60 days in most states. Medicare Advantage: 60 days for each appeal level. Medicaid managed care: varies by state, often 30–60 days. Write the deadline on your denial letter the day it arrives — missing it ends your appeal rights in most cases.

What should I do when my health insurance denies a claim?

Within 48 hours: request your Explanation of Benefits and denial letter, note the appeal deadline, identify the denial reason code, and contact your provider's billing department. Gather clinical records and request a letter of medical necessity from your doctor that addresses the specific denial reason. File a formal appeal through your insurer's portal — Availity, Express Scripts, OptumRx, or Caremark — not just a phone call to member services.

Are claim denials the same as coverage denials?

No. A claim denial rejects a specific submitted bill — usually due to authorization, coding, or medical necessity on that transaction. A coverage denial determines a service type is not a covered benefit under your plan regardless of how the claim was submitted. Both trigger appeal rights, but the documentation and legal arguments differ. Your EOB will indicate which type of decision was made.

Why Do Health Insurance Companies Deny Claims?

Q: Why do health insurance companies deny claims?

Health insurers deny claims when submitted services do not meet plan rules — most commonly missing prior authorization, medical necessity not documented, out-of-network billing, incorrect ICD-10 or CPT codes, step therapy requirements not met, or services excluded from your plan. Many denials result from documentation gaps rather than true coverage exclusions, which means a targeted appeal can reverse the decision.

By Medical Claims Advocacy Team•14 min read•Updated August 2026

Health insurance companies deny claims when submitted services do not meet plan rules — most commonly missing prior authorization, medical necessity not documented, out-of-network billing, incorrect codes, step therapy requirements, or plan exclusions. A denial is not final: federal law gives you the right to appeal under ERISA §503 or ACA §2719, typically within 60–180 days of the denial date.

How Health Insurance Claim Denials Actually Work

Key Takeaway: A claim denial means your insurer evaluated a submitted bill against your plan rules and refused payment. Your Explanation of Benefits shows the denied amount, reason code, and appeal deadline. The denial is about that specific transaction — not necessarily whether you are covered at all.

When patients ask why health insurance companies deny claims, they are usually staring at an Explanation of Benefits (EOB) showing a charge their plan refused to pay. A provider submitted a claim with your member ID, diagnosis codes (ICD-10), and procedure codes (CPT or HCPCS). The insurer's claims system — or a medical reviewer — evaluated that submission against your plan document and returned a denial.

This is a transactional decision: this bill, on this date, for this amount, was rejected. It is different from a coverage question about whether a type of service is included in your plan at all. Your EOB and formal denial letter will list a reason code — labels like CO-50 (medical necessity), CO-197 (prior authorization), or PR-96 (non-covered charge). That code tells you exactly what evidence your appeal must address.

I review claim denials every week across commercial, Medicare Advantage, and marketplace plans. The patients who recover payment fastest are not the ones who call member services repeatedly without a plan. They read the denial letter, match their documentation to the stated reason, and file a formal appeal before the clock runs out. For a full overview of your rights when a claim is denied, see our guide on whether insurance can deny a claim.

The 8 Most Common Reasons Health Insurers Deny Claims

Key Takeaway: Most claim denials fall into eight categories: missing prior authorization, medical necessity not met, out-of-network billing, coding errors, step therapy requirements, plan exclusions, benefit limits, and duplicate or timely filing issues. Each requires a different appeal strategy.

Prior authorization not on file (CO-197): Imaging, surgery, specialty drugs, and durable medical equipment often require pre-approval. Without it, the claim is denied even when the care was medically appropriate. Retroactive authorization is sometimes granted with strong clinical documentation.
Medical necessity not met (CO-50, PR-96): A medical director reviews whether the service meets the plan's clinical criteria. This is the most appealed denial category for MRIs, CT scans, physical therapy beyond visit limits, and specialty medications.
Out-of-network provider (CO-45, CO-96): Non-emergency care from providers outside your network may be denied or paid at reduced rates. Emergency services have federal protections under the No Surprises Act.
Coding mismatch (CO-4, CO-11): Wrong ICD-10 diagnosis or CPT procedure codes trigger automatic denials. Sometimes the fix is a corrected claim from your provider, not a full appeal.
Step therapy not satisfied: Pharmacy benefit managers require cheaper alternatives first. Denials for GLP-1 medications, biologics, and specialty drugs often fall here.
Plan exclusion or benefit limit: Cosmetic procedures, experimental treatments, or services beyond annual visit caps are denied when the plan document excludes them.
Duplicate claim (CO-18): The insurer believes the same service was already paid. Compare your EOBs and request claim history to identify the duplicate.
Timely filing limit exceeded (CO-29): The provider submitted the claim after your plan's deadline — often 90–365 days from the date of service. Appeal with proof of earlier submission attempts.

Industry data suggests commercial insurers deny roughly 10–20% of in-network claims on first submission, though rates vary widely by plan and service type. Many first-pass denials result from missing documentation rather than a true coverage exclusion — which means a well-built appeal has a real chance of reversal.

Why Insurers Use Prior Authorization and Medical Necessity Review

Key Takeaway: Prior authorization and medical necessity review are utilization management tools insurers use to confirm services meet plan criteria before or after payment. A denial under these programs often means documentation was missing — not that your doctor was wrong about your treatment.

Health insurance companies operate under contracts with employers, government programs, and individual members. Those contracts include utilization management programs — prior authorization, step therapy, quantity limits, and medical necessity review — designed to align spending with plan rules and clinical guidelines.

Prior authorization requires your provider to get insurer approval before delivering certain services. If the auth is missing, expired, or does not match the billed service, the claim is denied automatically — even when the care was appropriate. Medical necessity review goes further: a physician employed or contracted by the insurer evaluates whether the service meets the plan's clinical criteria, often referencing InterQual, MCG, or proprietary guidelines.

These programs generate a large share of patient frustration, but they also create an appeal pathway. When you submit a letter of medical necessity, clinical records, and failed-alternative documentation, you are directly addressing the criteria the reviewer applied. Appeals that speak the insurer's language — ICD-10 codes, guideline references, dated metrics — succeed at much higher rates than emotional complaints.

Common myth: Insurers deny claims randomly to avoid paying. While cost control is a business reality, most denials trace to specific, identifiable rule violations — missing auth, wrong code, incomplete records. Fix the rule violation in your appeal and you change the outcome.

Pharmacy vs. Medical Claim Denials: Different Rules, Different Portals

Key Takeaway: Prescription claim denials route through your Pharmacy Benefit Manager — Express Scripts, OptumRx, or Caremark — not your medical carrier. Submitting a medical appeal for a denied prescription will not work. Check the back of your insurance card to identify which entity handles each benefit.

Platform	Used By	Denial / Appeal Type
Availity	Anthem, BCBS, Humana, many regional plans	Medical claim denials; prior auth appeals
Express Scripts	Cigna, ESI-managed pharmacy benefits	Formulary exceptions, step therapy overrides
OptumRx	UnitedHealthcare, Optum-affiliated plans	Medication coverage and prior auth denials
Caremark (CVS)	Aetna, CVS Health plans	Specialty drug and prior auth denials
CoverMyMeds	Provider-initiated PA across PBMs	Track PA status; attach clinical info for appeals

Pharmacy denials have their own reason codes — STEP (step therapy), FORM (formulary exclusion), QTY (quantity limit) — that differ from medical claim remark codes. When your prescription is denied at the pharmacy counter, ask the pharmacist for the rejection code and which PBM processed the claim. That information determines your entire appeal strategy.

Weak vs. Strong Appeal Language (Before & After)

Key Takeaway: Insurer medical directors approve appeals with specific clinical evidence and plan citations — not emotional appeals. Replace vague statements with dated metrics, ICD-10 codes, and policy references tied to your denial reason code.

❌ Weak Statement	✅ Strong Statement
“I don't understand why my claim was denied. I have insurance.”	“I appeal denial #CLM-2026-88104 (CO-197). Prior authorization was submitted via Availity on 7/12/2026 (ref PA-33821) for CPT 73721 — lumbar MRI. Attached: auth confirmation, clinical notes documenting radiculopathy (ICD-10 M54.16), and 8 weeks failed conservative care.”
“My doctor ordered this test so it should be covered.”	“Medical necessity established per plan criteria Section 6.3: patient ICD-10 M25.561 with effusion, 6 weeks NSAIDs and PT without improvement. Knee MRI meets ACR Appropriateness Criteria for persistent joint pain after failed conservative treatment. Prescriber letter and PT records attached.”
“Please reconsider — I pay my premiums every month.”	“I formally request internal appeal under ERISA §503. Denial code CO-50 on claim dated 6/28/2026. Attached: letter of medical necessity, operative report, pathology results, and plan SBC page 14 confirming outpatient surgical benefits with prior auth. Request full claim file review.”

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What Patients Can Do When a Claim Is Denied

Key Takeaway: File your internal appeal before the deadline, attach a complete clinical packet, and request a written decision. Keep copies of everything you submit and document every phone call with date, representative name, and reference number.

Request your EOB and denial letter. Confirm the denial reason code, claim number, date of service, and appeal deadline. Write the deadline on your calendar the day the letter arrives.
Request your complete claim file. Under ERISA §503, you have the right to all documents the insurer used to deny the claim. Request this in writing within 10 days of receiving the denial.
Get a letter of medical necessity from your provider. It must address the specific denial reason — not a generic note saying you need the treatment. Include ICD-10 codes, treatment history, and failed alternatives.
Gather supporting records: clinical notes, lab results, imaging reports, prior auth submissions, pharmacy fill history, and any correspondence with the insurer.
Write your formal appeal letter. Cite your member ID, claim number, denial reason code, and the specific plan provision or federal law supporting payment.
Submit through the correct portal. Medical claims go through Availity or your carrier's member portal. Pharmacy claims go through Express Scripts, OptumRx, or Caremark. Confirm receipt and get a reference number.
Follow up at 14 and 30 days. Insurers must respond within 30 days for standard appeals. If denied again, request external review — independent reviewers overturn well-documented appeals roughly 40–55% of the time.

Your Legal Rights After a Health Insurance Claim Denial

Key Takeaway: Federal law guarantees your right to appeal claim denials. ERISA §503 covers employer-sponsored plans; ACA §2719 covers individual and marketplace plans. Both require insurers to provide a written decision, explain the reason, and give you access to your claim file upon request.

Under ERISA, your employer plan must allow up to 180 days to file an internal appeal from the date on your denial letter. The insurer must respond within 30 days for standard appeals — 72 hours for urgent appeals when delay poses a serious health risk. You also have the right to receive all documents the plan used to deny your claim.

ACA marketplace plans follow similar rules with 60-day appeal windows in most states. After an internal denial, you can request external review — an independent reviewer not employed by your insurer evaluates your case. Medicare beneficiaries follow a multi-level appeal process through Medicare.gov. Medicaid managed care appeals route through your state agency.

Missing your appeal deadline ends your right to challenge the denial in most cases. There are no automatic extensions. A phone call to member services is not a formal appeal — you must submit written documentation through your plan's official appeal channel to trigger ERISA and ACA legal protections.

Realistic Appeal Success Rates and Timelines

Key Takeaway: Appeals with complete clinical packets succeed roughly 40–55% on first internal submission. Incomplete appeals — missing medical necessity letters or failing to address the denial code — succeed less than 15%. Plan for 30–45 days for standard review.

I want to be direct: filing an appeal does not guarantee reversal. Insurers approve claims when the clinical record clearly meets their criteria. Your appeal letter frames that record, cites your legal rights, and connects the evidence to the specific reason your claim was denied.

Expedited (urgent) appeal: 72 hours — use when delay poses serious health risk
Standard internal appeal: 30 days from receipt of complete documentation
External review: 45–60 days after internal denial; independent reviewers overturn well-documented cases at similar 40–55% rates
Medicare Advantage: Multi-level process taking 60–90 days total

The single biggest factor in appeal success is whether your provider's letter of medical necessity addresses the specific denial reason code. Generic letters that restate the prescription or procedure without connecting to the insurer's criteria get denied again roughly 85% of the time. Ask your doctor to review the denial letter before signing anything.

Five Mistakes That Keep Denied Claims From Being Paid

Key Takeaway: Avoid resubmitting the same prior auth request after a denial — that is not an appeal. A formal appeal letter with new clinical evidence triggers different legal protections and a higher-level review standard.

Missing the appeal deadline. No exceptions in most plans. Calendar it the day you receive the denial letter.
Appealing to the wrong entity. Medical claim denials go to your carrier via Availity or your member portal. Pharmacy denials go to Express Scripts, OptumRx, or Caremark.
Generic provider letters. Demand a detailed letter addressing the specific denial code on your EOB — not a one-sentence note.
Not requesting your claim file. Insurers sometimes deny based on records you have never seen. ERISA gives you the right to review them.
Stopping after one denial. External review is your strongest remaining option, and many patients never use it. Add new evidence or clinical rationale each time you appeal.

Frequently Asked Questions

Answers to the most common questions about why health insurance companies deny claims and what you can do.

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Disclaimer: This article is for educational purposes only and does not constitute medical or legal advice. AppealFlow.net is not a healthcare provider or law firm. Success rates cited are estimates based on industry advocacy data and vary by plan. Always review appeal letters with your provider before submission. For medical emergencies, call 911. See our full disclaimer.