How to Appeal a Health Insurance Claim Denial (2026 Guide)

Start with the EOB — read the denial reason word for word

Pull the Explanation of Benefits (EOB) or the denial letter. Find the exact denial reason and the reason code. Insurance appeals only succeed when you address the specific reason cited. A general "this was medically necessary" letter doesn't work against a specific "this service is not covered for diagnosis code Z12.31" denial.

Common reasons (and what they really mean):

• "Not medically necessary." The insurer thinks the service or medication isn't clinically required. This is the most common medical-judgment denial. Eligible for external review.
• "Experimental or investigational." The insurer says the treatment doesn't have enough clinical evidence behind it. Also eligible for external review.
• "Not covered under this plan." The service is excluded by the plan's terms. NOT eligible for external review on its own — but if the exclusion is being applied incorrectly, that's appealable internally.
• "Prior authorization not obtained." Procedural denial. Often appealable if the situation was urgent or if there's evidence prior auth was actually obtained.
• "Out of network." Service was performed by a non-network provider. Appeals work if it was emergency care, if there was no in-network option, or under the No Surprises Act for ancillary providers.
• "Incorrect billing code." Provider billed something the insurer didn't recognize. Usually fixed by having the provider rebill with a corrected code — not a real appeal.
• "Maximum benefit reached." Plan-level limit. Hard to appeal but check the EOB for math errors.

The reason code matters. Write it down. Your appeal will address it directly.

Request your records first

Before you appeal, request three things in writing from the insurer:

1. The full denial letter with the specific reasons and the criteria used.
2. The clinical criteria or guidelines the insurer applied. Federal law (45 CFR 147.136) requires the insurer to provide these free on request.
3. A copy of the Summary Plan Description (SPD) and the relevant plan provisions.

If the denial was for medical necessity or experimental treatment, you're entitled to the actual scientific or clinical rationale, including the credentials of the reviewer who made the decision. Ask for that explicitly. Then your appeal can rebut their reasoning point by point.

The appeal letter structure

1. Header — name, address, member ID, claim number, date of service, denial date
2. Subject / RE: line — "Internal Appeal of Denial — Claim #X, Date of Service Y"
3. Statement of appeal — what you're appealing and the specific denial reason cited
4. Reason the denial is wrong — address the specific reason with documentation
5. Supporting clinical/factual evidence — letter of medical necessity, records, guidelines
6. Specific relief requested — "Reverse denial of Claim #X and process for payment of $Y"
7. Request for expedited review if applicable
8. Signature, date, contact info

Sample 1: Medical necessity denial appeal

[Your Name]
[Address]
[Phone] · [Email]
Member ID: [number]
Claim #: [number]
Date of Service: [date]
Provider: [provider name and NPI]

May 24, 2026

[Insurer Name]
Member Appeals / Grievances Department
[Address]

RE: Internal Appeal — Denial of Claim #[number]
    Date of Service: [date] · Member ID: [number]
    Denial Reason Code: [code from EOB]

I'm formally appealing the denial of the above claim. The denial
letter dated [date] states the service was denied as "not
medically necessary."

The denial is incorrect for the following reasons:

1. The treatment is the recommended standard of care for my
   diagnosis [ICD-10 code, condition name] per [cite specific
   guideline — NCCN, AHA, AMA, AAOS, etc.].

2. My treating physician has determined the treatment is
   medically necessary and has documented this in the attached
   letter of medical necessity dated [date]. The letter explains
   the clinical rationale, prior treatments attempted, and the
   expected clinical benefit.

3. The plan's own medical policy [cite policy number if known]
   includes this treatment as covered for patients meeting
   criteria [list]. Per my treating physician's documentation,
   I meet those criteria.

4. The reviewer who issued the denial was not credentialed in
   [specialty]. I'm requesting a peer-to-peer review with a
   physician credentialed in [specialty].

Attached:
  - Letter of medical necessity from [physician name, NPI], dated [date]
  - Relevant office notes from [date(s)]
  - Imaging/lab reports supporting the diagnosis
  - Citation to [specific guideline] supporting the treatment
  - History of conservative treatments attempted (if applicable)

I'm requesting:
  - Reversal of the denial
  - Payment of Claim #[number] in full at the in-network rate
  - A copy of all clinical criteria, guidelines, and reviewer
    credentials used in this determination

I'm available at (XXX) XXX-XXXX or [email].

Sincerely,
[Signature]
[Printed Name]

Sample 2: Prior authorization denial appeal

[Your Name]
[Address]
[Phone] · [Email]
Member ID: [number]
Claim #: [number]

May 24, 2026

[Insurer Name]
Member Appeals Department
[Address]

RE: Internal Appeal — Denial of Claim #[number]
    Denial Reason: Prior Authorization Not Obtained

I'm appealing the denial of the above claim, which was denied for
lack of prior authorization.

The denial is incorrect because:

1. The service was rendered on [date] under emergency conditions.
   Per 42 USC 1395dd and the No Surprises Act, prior authorization
   cannot be required for emergency services.

OR

1. Prior authorization was in fact obtained on [date] under
   authorization number [number]. The authorization is attached.
   The denial appears to be a clerical error.

OR

1. The service did not require prior authorization under the
   plan's policy at the time it was rendered. The plan's prior
   authorization list as of [date] is attached and does not
   include the CPT code(s) at issue.

I'm requesting reversal of the denial and payment of Claim
#[number] in full.

Attached:
  - Hospital/ER records establishing the emergent nature [if applicable]
  - Prior authorization confirmation [if applicable]
  - Plan PA list as of date of service [if applicable]

I'm available at (XXX) XXX-XXXX or [email].

Sincerely,
[Signature]
[Printed Name]

The letter of medical necessity

For medical-judgment denials, this letter from your treating physician carries more weight than your appeal letter. Your job is to get the physician to write it (or write a draft they can edit). It should include:

• Your diagnosis with ICD-10 code(s)
• The requested treatment and CPT/HCPCS code(s)
• Prior treatments attempted, dates, and outcomes ("step therapy" exhaustion)
• Clinical guidelines supporting the requested treatment (NCCN, AHA/ACC, AGA, AAOS, etc.)
• Peer-reviewed evidence if applicable
• Why alternative treatments are unsuitable
• Expected clinical benefit and risks of non-treatment
• The physician's credentials (specialty, board certification)

If your physician's office is slow, offer to write the draft. Hand them a 1-page letter with the citations done — they sign or edit. Most office managers prefer this.

Internal appeal timelines

• Pre-service denial (treatment hasn't happened): insurer must decide within 30 days
• Concurrent care decision (ongoing care reduction): 24 hours
• Post-service denial (treatment already happened): 60 days
• Urgent care: 72 hours
• Standard pre-service: 30 days under HHS rules, 45 days under ERISA in some cases

Most plans give you one or two levels of internal appeal. Read the denial letter — it should spell out how many levels are available and the timeline for each. You must "exhaust" internal appeals before requesting external review.

External review — the binding second opinion

If the insurer upholds the denial after internal appeals, you can request external review. An independent medical reviewer — not employed by the insurer — looks at the file and decides. About 40-50% of external reviews reverse the denial. The insurer is bound by the decision.

What's eligible for external review:

• Medical-judgment denials
• Denials of experimental or investigational treatment
• Rescission of coverage based on alleged misrepresentation

What's NOT eligible: contractual exclusions that don't involve medical judgment (e.g., "cosmetic procedures are excluded"), eligibility disputes, billing disputes.

To request external review:

• File within 4 months of the final internal appeal denial
• For state Marketplace and individual market plans: request through your state insurance department or the HHS-administered external review process (depending on state)
• For self-insured ERISA plans: request through the HHS-administered process or the insurer's designated Independent Review Organization (IRO)
• Standard external review: decided within 45 days. Expedited: 72 hours.

External review costs you nothing in most cases — the insurer pays the IRO fee.

If you're under ERISA

ERISA plans have a few important wrinkles:

• You must exhaust the plan's internal appeals before you can sue
• Once exhausted, you have a limited window (typically 1-3 years per plan terms) to file federal suit
• The court reviews the administrative record only — if you didn't put a document in during internal appeals, you usually can't add it later
• So load every document, every guideline, every clinical reference into your internal appeal — your appeal letter is building the trial record

What not to do

• Don't pay the bill while appealing. If you win, you'll be reimbursed only what you paid out of pocket up to the contracted rate, and any excess goes to the provider.
• Don't write a general appeal. Address the specific denial reason. Vague "this was needed" letters lose.
• Don't miss the deadline. 180 days for internal appeal, 4 months for external review. Calendar it.
• Don't appeal without records. Request the insurer's clinical criteria, the plan SPD, and the reviewer credentials before drafting.
• Don't ignore mental health/addiction denials. Mental Health Parity Act (MHPAEA) requires parity with physical health benefits. Many MH denials are illegal under federal law.

Special situations

Mental health and substance use treatment

Federal Mental Health Parity Act bars insurers from imposing more restrictive limits on mental health/SUD treatment than on medical/surgical. If your denial uses a stricter standard than what would apply to a comparable medical condition, that's a parity violation. Cite MHPAEA explicitly in the appeal.

Surprise out-of-network billing

The No Surprises Act (effective 2022) caps your liability for surprise out-of-network bills in emergency settings and for ancillary providers (anesthesiology, radiology, pathology) at in-network rates. If you got hit with a balance bill in these scenarios, the appeal cites the NSA.

Step therapy / "fail first" denials

Some plans require you to fail cheaper treatments first. If you've already failed them (or have contraindications), document that. Many states also have step therapy override laws requiring quick exemption processes.

Frequently Asked Questions

How long do I have to appeal a health insurance denial?

180 days from the date of the denial notice to file an internal appeal. Then four months from the final internal appeal decision to request external review.

What's the difference between internal appeal and external review?

Internal appeal: the insurer reviews their own denial. External review: an independent third-party medical reviewer overrules the insurer if appropriate. External review is binding on the insurer. About 40-50% of external reviews reverse denials.

Do I need a doctor to write the appeal?

Your doctor's letter of medical necessity is the single most important document in a medical-necessity denial. The appeal letter itself can come from you.

Is my plan covered by ERISA?

Most employer-sponsored plans are ERISA plans. Church plans, government plans, and individual market plans are NOT ERISA.

Can I get the appeal expedited?

Yes, if your health would be seriously jeopardized by waiting. Expedited internal appeals must be decided within 72 hours.

What if my appeal is still denied?

After exhausting internal appeals, request external review. If external review upholds the denial, your remaining options depend on plan type. Get a lawyer at this stage.

Related guides

• How to Write a Medical Hardship Letter
• How to Appeal an Unemployment Denial
• How to Appeal a Housing Denial