A denied claim isn't a final answer — it's the start of a process. Most denials can be appealed, and a significant percentage of those appeals succeed. Here's how to fight back.
Updated April 15, 2026
The most common denial reasons: prior authorization wasn't obtained, the service was deemed 'not medically necessary', the provider was out-of-network, or there was a billing code error. Each has a different fix.
Your insurer must send you an EOB explaining why the claim was denied. Look for the denial code — a short alphanumeric string like 'CO-50' or 'PR-96'. Each code maps to a specific reason. Your EOB will include a description.
Under federal law, you have the right to know exactly what medical criteria your insurer used to deny coverage. Ask for the 'clinical coverage criteria' or 'medical necessity guidelines' in writing.
Every insurer is required to have an internal appeal process. You typically have 180 days from the denial notice. Submit a letter with: your EOB, a letter from your doctor explaining medical necessity, and any supporting clinical documentation.
If your internal appeal is denied, you can request an independent external review — a third party reviews your case, and the insurer must comply with the decision. File through your state insurance commissioner or the federal Healthcare.gov portal.
New federal rules effective 2026 require insurers to resolve prior authorization requests faster and give clearer reasons for denials. If your plan is subject to these rules, expect faster turnaround on appeals.
Read your Explanation of Benefits (EOB)
Find the denial code and the specific reason for denial. Your insurer is required to send this within 30 days of the claim decision.
Call your insurer's member services
Use the number on the back of your insurance card. Ask for clarification on the denial reason and what documentation would support an appeal.
Get a letter of medical necessity from your doctor
Ask your provider to write a letter explaining why the service was medically necessary, citing relevant clinical guidelines and your diagnosis.
File your internal appeal in writing
Send your appeal letter + EOB + doctor's letter + any supporting records by certified mail. Keep copies of everything. Most plans require a decision within 30-60 days.
Request external review if denied again
If your internal appeal fails, you have the right to an independent external review. File through your state insurance commissioner or Healthcare.gov. The reviewer's decision is binding on the insurer.
Most plans give you 180 days from the date of the denial notice to file an internal appeal. Check your EOB for the exact deadline — it's required to be listed.
Prior authorization (PA) is approval from your insurer before you receive certain services or medications. Without it, the claim may be denied even if the care was medically necessary.
An internal appeal is reviewed by your own insurer. An external appeal goes to an independent organization. You can only request external review after exhausting internal appeals (or if your insurer doesn't respond in time).
Yes. Patient advocates, your state's insurance commissioner, and nonprofit organizations like Patient Advocate Foundation can assist. Many hospitals also have financial counselors who help with appeals.
A denial code (like CO-50 or PR-96) is a standard code that explains why a claim was denied or reduced. Your EOB includes the code and a plain-English description. Common codes: CO-50 means 'not medically necessary'; PR-96 means 'non-covered charge'.
See what’s on your card.
Take a photo. Get every number and term explained in plain English — free, for everyone.
Scan my insurance card →