Start here if a denial just landed on your desk.
What is an Explanation of Benefits (EOB)?
The document a payer sends after processing a claim — how to read every section and what triggers your appeal rights.
Read the guideFundamentalsCARC and RARC codes explained
The standardized codes that tell you exactly why payment differed from what was billed, and what each group means for your next step.
Read the guideFundamentalsAppeal deadlines by plan type
ERISA, Medicare, ACA, and Medicaid each set different windows. Miss one and the door usually closes for good.
Read the guideFundamentalsHow to write a medical-necessity appeal letter
The structure, evidence, and legal grounding that actually moves a denial reviewer — from the opening paragraph to the enclosures list.
Read the guideAppeal strategy by CARC code.
Each denial code carries a different argument, a different evidentiary standard, and a different legal hook. Start with the code on your EOB.
Medical necessity denied
The payer determined the service wasn't medically necessary. One of the most appealable denials in the system — when you build the record correctly.
Appeal strategyCO-97NCCI bundling edit
CMS's Correct Coding Initiative says two procedures can't be billed separately. Modifiers 59 and the X-modifiers exist precisely because there are exceptions.
Appeal strategyCO-45Charge exceeds allowed amount
In-network, it's usually a contractual write-off. Out-of-network, the methodology behind the allowed amount is often the real question.
Appeal strategyLevels, reviews, and your rights.
How the appeal process works
Internal levels, external review, and the deadline that gates each stage — mapped end to end so you know where a denial actually stands.
Read the guideExternal review, by state
When a plan upholds its own denial, an independent reviewer can still overturn it. Who runs the process in your state, and how to invoke it.
Read the guideReference, by your role.
For physicians
All practice references →The billing & appeals glossary
Every term behind a denial, in plain language.
Ready to appeal?
Upload the denied EOB and Merits builds the cited, signable letter — every argument anchored to the source document that governs your plan type.