The 2-minute version
The hardest part is not the writing. It is realizing the appeal is winnable. KFF's analysis of CMS transparency data found marketplace insurers denied 19% of in-network claims in 2024 — about 85 million claims denied in a single plan year — yet fewer than 1% of denied claims were ever appealed. Among the appeals patients did file, roughly one in three succeeded at the internal stage, before external review even started. (KFF, 2024 data)
Step 1: Read the denial letter carefully
The denial letter (the Explanation of Benefits or a separate Notice of Adverse Benefit Determination) is legally required to tell you three things: the specific reason the claim was denied, the rule or policy the insurer applied, and the deadline and procedure for appealing. (29 CFR 2560.503-1)
Pull out the denial reason code, the clinical policy bulletin number (often something like "CPB 0123" for Aetna or "MPB-2024-005" for Anthem), and the filing deadline. Those three pieces of information drive everything else.
Need help decoding the denial? Browse the most common reason codes: by denial reason →
Step 2: Lock in your deadline
Deadlines are absolute. Missing the internal appeal window almost always forfeits the right to external review afterward. Pin the calendar before you do anything else.
| Plan type | Internal appeal | External review | Expedited |
|---|---|---|---|
| ERISA group plan | 180 days | 120 days after final internal denial | 72 hours |
| ACA marketplace plan | 180 days | 120 days | 72 hours |
| Medicare Advantage (Part C) | 60 days (reconsideration) | Auto-forwarded if upheld | 72 hours |
| Original Medicare | 120 days (redetermination) | 5 levels through ALJ + MAC | 72 hours |
| Medicaid managed care | 60 days (typical) | State fair hearing in parallel | 72 hours |
Federal sources: U.S. Department of Labor / eCFR, Centers for Medicare & Medicaid Services / eCFR, Centers for Medicare & Medicaid Services, HealthCare.gov. Confirm against your denial letter — state-regulated plans sometimes set a shorter window.
Step 3: Gather the right evidence
An appeal wins on records, not adjectives. Pull the following before you write a word:
- The denial letter and the original claim or prior authorization request.
- The insurer's clinical policy bulletin by name and number. ERISA requires the plan to provide it on request, free of charge.
- A letter of medical necessity from the treating physician — not a form letter; one that addresses the policy criteria.
- Relevant office notes from the past 12 months.
- Imaging and lab reports that map to the policy criteria.
- Specialty-society guidelines (NCCN for oncology, ACR for radiology, AAN for neurology, AAO for ophthalmology, ASAM for addiction medicine).
- Documentation of any prior therapies tried and failed, if step therapy is at issue.
Step 4: Write the appeal letter
Three pages or fewer for the letter itself, plus attachments. The reviewer reads dozens of files a week — brevity and structure win. Lead with the decision you want, then the policy citation, then the evidence mapping.
- Header — member name, member ID, claim number, date of denial, date of service, the decision you want ("overturn the denial and authorize CPT 12345").
- Cite the policy — "Your denial cites Clinical Policy Bulletin CPB 0123 (rev. 2025-04). I am writing to demonstrate that the criteria in CPB 0123 are met."
- Criterion-by-criterion mapping — for each numbered criterion in the policy, quote it, then point to the record that satisfies it. Attach the record as a numbered exhibit.
- Specialty guidelines — cite NCCN / ACR / AAN with the exact recommendation number.
- Letter of medical necessity — referenced as Exhibit A and attached.
- Decision requested + signature — restate the outcome you want and sign.
For a worked template by topic, see our appeal-letter structure guide and the how-to-get-the-medical-policy guide.
Step 5: Submit and track
Send the appeal two ways — by certified mail with return receipt, and through the insurer's member portal message center. The certified-mail receipt is your proof of timely filing; the portal message creates a timestamped record inside the insurer's own system.
The clock starts the day the insurer receives the appeal. Pre-service appeals must be decided in 30 days; post-service appeals in 60 days. If they miss the window, you may be deemed to have exhausted internal review and can move straight to external review. Centers for Medicare & Medicaid Services / eCFR
Step 6: External review — the binding step
If the internal appeal is upheld, the next move is external review by an Independent Review Organization (IRO). Federal external review applies to ERISA and marketplace plans; state external review applies to fully-insured plans. Either way, the IRO is independent of the insurer and the decision is binding: if the IRO sides with you, the insurer must pay.
You have 120 days from the final internal denial to file. There is no cost to the consumer. For urgent cases, external review runs in parallel with internal review and decides within 72 hours. HealthCare.gov
Appeals by plan type
The rules above are the federal baseline. Specifics vary:
- ERISA self-funded employer plans. Federal external review through the HHS-administered IRO list.
- Fully-insured employer plans. State external review by an IRO contracted by the state insurance department.
- ACA marketplace plans. Same as ERISA / state-insured, depending on funding structure. HealthCare.gov publishes the path. HealthCare.gov
- Medicare Advantage. Five-level appeal: plan reconsideration → IRE reconsideration → ALJ hearing → Medicare Appeals Council → federal court. Centers for Medicare & Medicaid Services
- Medicaid managed care. Plan appeal plus a state fair hearing right that can run in parallel.
Browse insurer-specific addresses, phone numbers, and policy bulletin lookups: all insurers →
Expedited (urgent) appeals
The standard for expedited review is whether a delay would seriously jeopardize life, health, or the ability to regain function. Common qualifying situations: an ongoing inpatient stay, active cancer treatment, urgent surgery, behavioral health crisis, or denial of a medication that prevents acute decompensation.
To request expedited review: have the treating physician fax a written statement supporting urgency, file by phone and fax simultaneously, document the name and time of every person you spoke with. Internal expedited review must decide within 72 hours. For urgent cases you may file expedited internal and external review in parallel. Centers for Medicare & Medicaid Services / eCFR
Common mistakes that lose appeals
- Emotion without records. An appeal grounded in how sick the patient is, without a single citation to the policy, loses almost every time.
- Treating the policy as optional. Insurers reverse when their own bulletin says they should. Never argue around the policy — argue inside it.
- Sending originals. Send copies. Keep originals.
- Missing the deadline by a day. Mail two weeks early. Confirm receipt.
- Skipping the letter of medical necessity. The treating physician's statement is the single most-cited element of overturned appeals.
- Stopping after one internal denial. Most plans allow two levels of internal appeal before external review opens.
Common questions
How long do I have to appeal a denied health insurance claim?+
On ERISA group plans and ACA marketplace plans you have 180 days from the date of the denial notice to file an internal appeal (29 CFR 2560.503-1 and 45 CFR 147.136). After the final internal denial you have 120 days to request external review. Medicare Advantage uses a 60-day window for the first reconsideration.
What is the success rate of a health insurance appeal?+
Hard data on commercial appeals is thin because fewer than 1% of denied marketplace claims are ever appealed. Among those that are appealed, KFF's 2024 analysis found insurers upheld 66% of internal appeals — meaning roughly one in three internal appeals succeeds. External review by an Independent Review Organization reverses a further share and is binding on the insurer.
Do I need a lawyer to file an appeal?+
Not for most internal appeals. A self-help appeal works when it cites the insurer's own clinical policy bulletin by name and maps your medical records to its criteria, one by one. A lawyer becomes useful after a final external review denial or when ERISA litigation is the next step.
Can I file an urgent appeal?+
Yes. If waiting on a standard appeal would seriously jeopardize your life, health, or ability to regain function, you can request an expedited appeal. The insurer must decide within 72 hours. The treating physician submits a written statement supporting urgency. For urgent cases you can file internal and external review at the same time.
What documents go into a strong appeal?+
The denial letter (EOB), the insurer's clinical policy bulletin cited by the denial, a letter of medical necessity from the treating physician, the past 12 months of relevant office notes, imaging or lab reports that match the policy criteria, and specialty-society guidelines (NCCN, ACR, AAN, AAO).
What if my insurer ignores the deadline?+
If the insurer fails to decide within the required timeframe — 30 days for pre-service, 60 days for post-service on ERISA plans — you may be deemed to have exhausted internal appeals and can go straight to external review. Document every contact attempt in writing.
Does external review actually overturn denials?+
Often, yes. External review is conducted by an Independent Review Organization (IRO) not affiliated with the insurer, and the IRO's decision is binding on the insurer. KFF reports more than 5,800 external appeals filed by marketplace enrollees in 2024 — small in absolute terms because most patients give up at the internal stage.
Upload the EOB. You get the cited policy, the reason code, and the exact deadline you are working against.
Sources: KFF — Claims Denials and Appeals in ACA Marketplace Plans in 2024; U.S. Department of Labor / eCFR — 29 CFR 2560.503-1 — Claims procedure (ERISA); Centers for Medicare & Medicaid Services / eCFR — 45 CFR 147.136 — Internal claims and appeals and external review processes; HealthCare.gov — Appealing a health plan decision; Centers for Medicare & Medicaid Services — Medicare Parts C and D Appeals Process. Last verified: 2026-06-16.