What to Do if Insurance Denies a Claim
Getting a denial letter does not mean it is over. Over 50% of insurance denials that are appealed are successfully overturned — but less than 1% of patients ever file an appeal. Here is exactly what to do, from someone who processed claims from the inside.
Most insurance plans give you between 30 and 180 days from the denial date to file an internal appeal. Missing this deadline permanently forfeits your right to challenge the decision — even if the denial is clearly wrong. The first thing to do after reading this page is find your deadline and put it in your calendar.
Here is what to do right now — in order
The 6 Most Common Reasons Insurance Denies Claims
Before you can fight a denial effectively, you need to understand why it happened. The denial letter must state the reason by law. Find your reason type below — each requires a different appeal strategy.
Medical necessity denial
The insurer says the treatment was not medically necessary. This is the most common denial — and the most winnable on appeal when supported by strong physician documentation.
Prior authorization not obtained
The treatment required advance approval that was not obtained before the service was performed. Often an administrative failure by the provider rather than a genuine coverage issue.
Out-of-network provider
You were treated by a provider outside your plan's network — sometimes without knowing it, particularly in hospital settings where individual specialists may be out-of-network.
Experimental or investigational
The insurer classifies the treatment as experimental even when it is widely accepted clinical practice. This label is sometimes applied to newer treatments that have strong evidence behind them.
Coverage exclusion
The insurer claims the service is excluded under your plan. Exclusions are often written narrowly — review the exact policy language carefully before accepting this denial.
Billing or administrative error
A wrong billing code, incorrect patient information, or other administrative error caused the claim to be processed incorrectly. Often the easiest type of denial to resolve.
What to Do — Step by Step
Follow these steps in order. Each one builds on the last. The most important thing is to act quickly — your deadline is counting down from the date on that denial letter.
Get everything in writing immediately
If you received a verbal denial by phone, call back and request the formal written denial letter and your Explanation of Benefits (EOB). By law, the denial letter must include the specific reason for the denial, the clinical criteria or policy provision used to make that decision, and information about how to appeal.
If the letter does not include all of this, call your insurer and demand a more detailed explanation in writing before you do anything else.
Find your appeal deadline and protect it
Your appeal deadline is one of the most important pieces of information in the denial letter. Write it down, put it in your calendar, and set a reminder for 14 days before it arrives. Missing this date permanently ends your right to appeal — even if the denial is clearly wrong.
Request the clinical criteria used to deny your claim
Your insurer used specific clinical guidelines to determine the treatment was not medically necessary or covered. You have the legal right to request these criteria in writing. Call member services and ask: "What specific clinical criteria and policy provisions were used to deny my claim dated [date], claim number [number]?"
Once you have these criteria, give them to your doctor. A Letter of Medical Necessity that directly addresses and rebuts the insurer's specific criteria is far more effective than a general statement of necessity.
Get a Letter of Medical Necessity from your doctor
This is the single most powerful document in any insurance appeal. Ask your doctor to write a detailed letter that explains why the treatment is medically necessary specifically for your condition, what alternatives were considered and why they are inadequate, what the consequences of not receiving the treatment would be, and — critically — directly addresses the clinical criteria your insurer cited to deny the claim.
File your written internal appeal
Every insurance plan must have an internal appeals process. File your appeal in writing — not just by phone — and send it by certified mail so you have proof of the date filed and confirmation of delivery.
Your appeal should clearly state which denial you are appealing and the claim number, explain why the denial is incorrect, reference your doctor's Letter of Medical Necessity, include all supporting medical records, and request a response within the legally required timeframe.
If the internal appeal fails — request an Independent External Review
If your insurer upholds the denial after your internal appeal, you have the right to an Independent External Review under the Affordable Care Act. This means an independent organization — completely separate from your insurer — reviews your case and makes a binding decision your insurer must comply with.
You must request the external review within 60 days of the final internal denial. There is no cost to you for this process. External reviews overturn insurer decisions approximately 40% of the time — meaning patients who pursue this step win nearly half the time.
Escalate further if needed
If external review does not resolve it, you have additional escalation paths available:
File a complaint with your state Insurance Commissioner — they regulate insurer conduct and can apply significant pressure. This is free and can sometimes result in a reversal without further legal action.
Contact your employer HR department — if your insurance is through your employer, HR has leverage with the insurance company that individual members do not have. Escalating through HR can sometimes resolve denials faster than the formal appeals process.
Consult a patient advocate or healthcare attorney — for large denials, many patient advocates and attorneys work on contingency for insurance disputes, meaning you pay nothing unless you win.
File with the Consumer Financial Protection Bureau (CFPB) — if the denied claim has gone to collections, you can file a complaint with the CFPB.
The Full Appeals Escalation Path
Think of your appeal as a ladder. Start at the bottom and only move up if the step below fails. Most denials are resolved at Step 1 or 2 — you rarely need to reach Step 5.
Use These Tools Right Now
Every tool you need to file a strong appeal — all free, all built from healthcare administration experience.
Insurance Denial Appeal Builder
Generate a complete, personalized appeal letter tailored to your specific denial type in under 3 minutes. Includes a deadline calculator, 6 denial types, and formal + email versions.
Free Insurance Appeal Checklist
The complete 20-item appeal filing checklist — with a denial reason decoder, deadline tracker, and supporting documents guide. Interactive — use it directly in your browser.
Hospital Financial Assistance Guide
If your appeal fails, financial assistance programs exist that most patients never hear about. Every nonprofit hospital is legally required to offer them — learn how to apply.
✓ Immediate action checklist — do these today
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