Billing Reference Desk — For Billing Staff & RCM Teams

Reference guides

What fills the denial queue.

The three that crowd a biller's queue — the filing clock that can forfeit a claim, the modifier auditors scrutinize most, and the rejections that never reach the payer.

CO-29

Timely Filing

Filing windows by payer, the proof that reverses a CO-29, and how the appeal is argued.

Read the guide MOD 25

Modifier 25

When it applies, the documentation an auditor expects, and why payers single it out.

Read the guide 277CA / 835

Rejections vs. Denials

How a 277CA rejection differs from an 835 denial, and the separate workflow each one needs.

Read the guide

Denial codes

The codes that hit your queue.

Browse all denial codes

Tap a code for the argument, the evidentiary standard, and an honest read on whether it's worth appealing.

CO-16Rarely — usually a fix

Claim lacks information or has a billing error.

Appeal strategy

CO-29Sometimes

The timely-filing limit has expired.

Appeal strategy

CO-18Sometimes

Flagged as an exact duplicate claim.

Appeal strategy

CO-4Sometimes

Procedure inconsistent with the modifier.

Appeal strategy

CO-97In-depth guide

Bundled under an NCCI edit.

Appeal strategy

CO-22Sometimes

May be covered by another payer (COB).

Appeal strategy

CO-109Rarely — usually a fix

Not covered by this payer or contractor.

Appeal strategy

PR-1Patient's share

Deductible — the patient's responsibility.

Appeal strategy

Explore the library

Where to go next.

For physiciansReimbursement, prior auth, and plan-type rules.Denial code guideEvery CARC code, with an honest read on the odds.The full libraryEOBs, CARC codes, deadlines, and the appeal process.GlossaryEvery term behind a denial, in plain language.

When the next appeal is due.

Upload a denied EOB and Merits returns a cited, signable appeal — the argument, the records to attach, and where and when to file it — for your provider to approve in minutes.

Appeal a denial →