Insurance & medical bills guide
How to Appeal an Insurance Denial: Step-by-Step (Internal vs External Review)
You have the legal right to appeal any health-insurance claim denial. The process has two stages: (1) an internal appeal to your insurer (usually due 180 days from the denial), and (2) an external review by an independent third party if the internal appeal is denied. External review is free, decided by doctors not your insurer, and overturns a meaningful share of denials. The single biggest mistake people make is waiting — deadlines are strict, so start the appeal the day you read the denial.
Insurance companies deny claims every day — more than 1 in 7 in-network claims were denied in recent federal data, and the rate is far higher for prior-authorization services. A denial notice is not a verdict; it's an invitation to fight with documentation. Patients who appeal win surprisingly often: external review overturns denials in many cases, and the deck is stacked far less against you than it feels.
This guide walks the whole lifecycle: reading the denial, gathering evidence, writing the appeal, hitting the deadlines, and escalating to external review. Everything here is free — the appeal letter generator at the bottom builds your first letter in one click, no account.
First, decode the denial — why were you denied?
Your EOB (explanation of benefits) or denial letter always carries a reason code. The first letter matters: CO means contractual (often not your fault, the provider's write-off), PR means patient responsibility (you may actually owe), OA is usually coordination of benefits. Look up your exact code — each one has a specific fix and specific appeal strategy.
- CO-16 claim lacks information → provider must correct & resubmit
- CO-50 not medically necessary → the classic appealable clinical denial
- CO-197 prior authorization not obtained → request retro-authorization first
- CO-29 timely filing → provider error, usually reversible with one letter
- PR-1 / PR-2 / PR-3 deductible / coinsurance / copay → usually legitimate, verify the math
Check the clock — internal appeal deadlines by plan type
Deadlines are the #1 reason appeals fail. They differ by plan type. Count from the date ON the denial notice, not the date you opened it.
- Employer plans & individual ACA plans (ERISA): 180 days from denial notice to file internal appeal, then 4 months to request external review
- Medicare: 120 days for redetermination; escalate to reconsideration with QIC, then ALJ hearing
- Medicaid: 90 days in most states (some 60–180)
- Most plans: 30–60 days after internal denial to request external review
Gather the evidence that actually wins appeals
Insurers deny for clinical or administrative reasons — and the evidence is different for each. The strongest appeals answer the denial letter's stated reason directly, point by point. A generic letter is how you lose; a letter that shows a mismatch between the denial reason and your records is how you win.
- The denial letter + the exact policy/clinical-criteria language it cites
- Your doctor's note that specifically documents why the service was necessary
- Test results, imaging reports, specialist referrals
- Prior authorization records (if the denial is about authorization)
- Anything showing you were told the service would be covered (call transcripts, patient-finance estimates, plan documents)
Internal appeal — how to file it
The internal appeal is your first formal shot. Mail or submit through the insurer's portal a letter that states your claim number, restates the denial reason, and explains — with evidence — why the denial is wrong. Keep a copy of everything. Insurers must respond within 30 days for prospective denials (urgent: 72 hours) and generally within 30–60 days for retrospective ones.
- Use the appeal letter generator below as your starting draft
- Attach every piece of evidence, organized and labeled
- Send by certified mail or screenshot the portal submission
- Note the insurer's appeals address/portal from your denial notice
External review — your free second shot
If internal appeal is denied, every governed health plan must allow an external review by an independent medical reviewer — at no cost to you. The reviewer is not affiliated with your insurer. Patients win external reviews a substantial share of the time, yet most people never request one because it sounds intimidating. It is a form; your doctor can help with the medical summary.
- Federal law (and state law in every state) guarantees external review for most plans
- You usually have 4 months from the internal denial
- The reviewer decides based on your file + independent medical judgment
- If your plan is self-funded ERISA, appeal through the ERISA process and you keep the right to sue under ERISA §502 — external review is still available
Special situations: retroactive denials & balance bills
Some denials need a different playbook. Retroactive denials (insurer pays, then claws back months later — common with UHC 'review' programs) require you to demand the specific medical-reasoning and re-attach prior-authorization history. Balance bills after a denial are governed by your state's rules and provider contracts — if the provider failed to obtain authorization, many states forbid billing you.
- Retroactive denial → see our retroactive-denial guide, demand the clinical reasoning in writing
- Provider billing you after a denial → check whether the provider or insurer broke the process; get it in writing
- Out-of-network emergency care → federal No Surprises Act protects you; balanced bills over your in-network cost-share are prohibited
Look up your denial code
If your EOB shows one of these, jump straight to the specific fix:
📄 Generate a free appeal letter
Answer three questions and get a ready-to-send insurance appeal letter — no registration, no account, instant download.
Build my appeal letter →How long do I have to appeal an insurance denial?
Most plans give you 180 days from the denial notice for the internal appeal (ERISA and individual/ACA plans). Medicare gives 120 days. After the internal appeal is denied, you typically have 4 months to request external review. Check the deadline printed on your denial notice — it controls.
Does it cost anything to appeal?
No. Both internal appeal and external review are free for the patient. You pay only for your time and, optionally, certified mail. Anyone charging you to 'file an appeal' is selling convenience, not a requirement.
How often do insurance appeals succeed?
Often enough to make it worth trying. State external-review programs overturn denials in a large share of cases (federal data shows patients win a substantial minority of commercial external reviews), and many internal appeals succeed when the provider supports the evidence. Medical-necessity denials (CO-50) are among the most often overturned.
Can I appeal a claim I already paid?
Yes. Paying a bill does not waive your appeal rights, and you can appeal a processed 'patient responsibility' amount too. If your appeal succeeds after you've paid, the insurer reprocesses the claim and the provider refunds the difference.