How to Appeal a Denied Medical Claim: Step-by-Step

A denied claim is not a lost claim. Every payer has an appeal process, and a large share of denials are administrative — missing information, eligibility mismatches, authorization issues — that reverse cleanly once the right documentation reaches the right reviewer. The difference between teams that recover denial revenue and teams that write it off is process: classify the denial, meet the deadline, document the case, and follow up relentlessly. Here's the full workflow.

Step 1: Read and classify the denial

Start with the remittance advice (the 835 ERA or paper EOB). Every denial carries a Claim Adjustment Reason Code (CARC) and usually a Remittance Advice Remark Code (RARC) explaining what the payer wants. Common examples:

Code	Meaning	What it tells you
CO-16	Claim lacks information needed for adjudication	Something is missing — find out what and resubmit or appeal with it
CO-96	Non-covered charges	Medical necessity or benefit exclusion issue — needs a clinical case
CO-97	Benefit for the service is included in another payment	Bundling denial — check NCCI edits and modifiers
CO-197	No precertification/authorization	Auth was missing — appeal with the auth number or retro auth
CO-29	Time limit for filing expired	Timely filing — appeal only if you can prove on-time submission

Classify every denial into one of four buckets: administrative (missing/invalid data), coverage (medical necessity, non-covered), authorization (missing or invalid auth), or timely filing. Your fix strategy depends entirely on the bucket. For a full breakdown, see our guide to the 7 most common denial reasons and how to fix each.

Step 2: Check the appeal deadline — first, not last

This is the step teams skip and regret. Appeal windows are payer-specific and strict. Many commercial payers allow 90–180 days from the denial date. Medicare Part B redeterminations must be requested within 120 days of the date on the remittance advice. Some payers give as little as 30–60 days.

Build the habit: the moment a denial is worked, stamp it with its appeal deadline. A denial appealed one day late is usually a denial forever. Keep a payer-by-payer reference — our timely filing limits guide covers submission deadlines, and the same discipline applies to appeal windows.

Step 3: Gather your documentation

Assemble the evidence before you write a word. What you need depends on the denial bucket:

Administrative denials: the corrected data — member ID, dates of service, NPI, diagnosis pointers. Often the "appeal" is a corrected claim, not a letter.
Eligibility denials: proof of active coverage on the date of service (eligibility verification screenshots, payer portal printouts).
Authorization denials: the authorization number, approval dates, and approved units. If no auth was obtained, document any retro-authorization or medical emergency justification.
Medical necessity denials: chart notes, operative reports, lab/pathology results, and published clinical guidelines supporting the service.
Timely filing denials: proof of timely submission — clearinghouse acceptance reports and 277CA claim acknowledgments showing the payer received the claim in time.

Step 4: Write the appeal letter

Keep it to one or two pages. Reviewers process hundreds of these; clarity wins. Every appeal letter needs:

Header: patient name, member ID, date(s) of service, claim number, and the denial reason code.
Opening: one sentence stating you're appealing the denial and requesting reprocessing and payment.
The case: 2–4 short paragraphs addressing the specific denial reason. Reference the attached documentation by name ("see attached operative report, pages 3–5").
The ask: a specific request — "reprocess claim #12345 and issue payment of $X."
Attachments list: enumerate everything enclosed so nothing gets separated.

For authorization-related denials, our prior authorization appeal letter guide includes a full template outline.

Step 5: Submit to the right place, the right way

Payers have separate addresses, fax numbers, and portals for appeals versus initial claims — sending an appeal to the claims address is a classic way to lose weeks. Check the payer's provider manual or the denial notice itself for the appeals submission instructions. Submit electronically where possible (payer portals timestamp receipt), and keep the confirmation. If faxing, keep the transmission report.

Step 6: Track and follow up on a cadence

An appeal submitted is not an appeal resolved. Log every appeal with its submission date and the payer's stated turnaround time (often 30–60 days). Follow up at the halfway mark and again at the deadline. When you call, get a reference number and the reviewer's name. Escalate stalled appeals — a second-level review or peer-to-peer often moves what the first queue won't.

When the first appeal is denied

Don't stop at level one. Second-level appeals and peer-to-peer reviews put the case in front of clinical reviewers instead of administrative ones, and they overturn denials the first level wouldn't touch. Bring whatever the first denial said was missing, plus anything new. For fully insured plans, most states offer an external review process through the insurance department as a final recourse.

A note on prevention: the cheapest appeal is the one you never file. Claim scrubbing catches missing data, eligibility, and coding errors before submission — most administrative denials are preventable at the front end.

Common appeal mistakes

Appealing without reading the reason code — sending a medical-necessity letter for a missing-information denial.
Missing the deadline — the single most expensive mistake in denial management.
Resubmitting instead of appealing — a duplicate claim can create a duplicate-denial; know which one the payer wants.
No documentation attached — an appeal letter without evidence is just a complaint.
No tracking — appeals that aren't followed up die quietly in payer queues.

Appeal vs. corrected claim vs. reopening: which one?

Not every denied claim needs a formal appeal. Using the wrong vehicle wastes weeks:

Corrected claim: use when the denial was caused by your data — wrong code, missing modifier, transposed member ID. Fix the data and resubmit with the payer's corrected-claim indicator (often a claim frequency code of 7). This is usually faster than an appeal.
Formal appeal: use when you disagree with the payer's decision — medical necessity, bundling you believe is wrong, authorization disputes. This is the letter process described above.
Reopening: some payers (including Medicare) allow minor errors to be fixed through a "reopening" — a lighter-weight correction process for clerical mistakes. Check the payer's rules; it's faster than an appeal when it applies.

When in doubt, call the payer's provider line and ask which path they want. A two-minute call can save a three-week wrong turn.

Your appeal packet checklist

Before anything goes out the door, confirm the packet has:

Appeal letter with claim number, dates of service, and reason codes referenced
Copy of the original claim
Copy of the remittance advice / EOB showing the denial
All supporting documentation, labeled and referenced in the letter
Proof of timely submission if appealing a timely-filing denial
Submission confirmation (portal receipt, fax transmission report)
A diary entry: follow-up date set, owner assigned

Illustration of appeal documentation being prepared

Steps in every appeal: classify the denial, check the deadline, gather documentation, write the letter, track and follow up.

Frequently asked questions

How long do I have to appeal a denied claim?

It depends on the payer. Many commercial payers allow 90 to 180 days from the denial date. Medicare Part B redeterminations must be requested within 120 days of the remittance advice date. Always check the specific payer's appeal deadline — missing it usually ends the claim.

What should an appeal letter include?

Patient name and member ID, date(s) of service, claim number, the denial reason code, a clear statement of why the denial should be reversed, supporting clinical documentation, and a specific request to reprocess and pay. Keep it factual and under two pages.

Can I appeal a timely-filing denial?

Sometimes. If you can prove the claim was submitted on time — clearinghouse acceptance reports and 277CA acknowledgments — submit that proof with the appeal. If the claim was genuinely late, most payers will not overturn a timely-filing denial.

What if my first appeal is denied?

Request a second-level or peer-to-peer review, which puts the case in front of a medical reviewer rather than an administrative one. Add any documentation the first denial said was missing. For fully insured plans, an external review through the state insurance department is a later option.