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CARC code 18 — Exact duplicate claim/service

Sarah Chen, RN-BSN, CPCSarah leads InsureDefense's clinical review. 12 years working appeals at a major US payer plus 4 years as a patient advocate.

What CARC 18 means

Duplicate or timely-filing denials usually mean the claim was filed past the insurer's filing window or duplicates an earlier submission. These are almost always provider-side issues.

How to appeal a CARC 18 denial

Most of these resolve when the provider's billing office addresses the submission. Consumer appeals are usually not the right path for this category.

What InsureDefense adds

Our triage classifies your specific denial into one of ten categories and tells you exactly what evidence appeals like yours typically need. For CARC 18 denials, we usually recommend the tier that fits the category of the denial — sometimes Strong ($249) is enough, sometimes Premium ($499) with plan-language citations and peer-reviewed support is the right path. The free triage shows you which.

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Frequently asked questions

What does CARC code 18 mean?
Exact duplicate claim/service. Duplicate or timely-filing denials usually mean the claim was filed past the insurer's filing window or duplicates an earlier submission. These are almost always provider-side issues.
Can I appeal a CARC 18 denial?
Most of these resolve when the provider's billing office addresses the submission. Consumer appeals are usually not the right path for this category.
How long do I have to appeal?
Under federal law, you generally have 180 days from receiving the denial notice. The exact deadline is on the denial letter.
Not legal, medical, or insurance advice.

InsureDefense is not a law firm, insurer, medical provider, or claims adjuster. We do not provide legal, medical, or insurance advice. We prepare appeal documents based on the information you provide. We do not guarantee approval, payment, coverage, or reimbursement. For urgent medical situations, contact your doctor, insurer, or emergency services directly.