Medical Billing · Denial Codes
CO-97 and CO-45 Denial Codes: What They Mean and How to Fix Them
CO-97 and CO-45 are two of the most common adjustment codes on a medical remittance advice, and understanding the CO-97 and CO-45 denial code meaning is the difference between writing off revenue and recovering it. In short: CO-45 means your charge exceeded the payer's allowed amount — a contractual write-off — while CO-97 means the service was bundled into another payment and not paid separately. One is usually legitimate; the other is often recoverable. Here's how to tell them apart and what to do about each.
What CO-45 means
Direct answer: CO-45 means the amount you billed is more than the payer's allowed amount under your contract or their fee schedule. The gap between your charge and the allowed amount is a contractual adjustment — you agreed to it when you signed the payer contract, and you cannot bill it to the patient.
Most of the time CO-45 is simply how the math works: you charge your standard rate, the payer pays their contracted rate, and the difference is written off. It is an adjustment, not a true denial. The catch is that "allowed amount" is only correct if the payer applied the right fee schedule — and they don't always.
What CO-97 means
Direct answer: CO-97 means the benefit for the service is already included in the payment for another service that was adjudicated, so it is not reimbursed separately. In plain terms, the payer bundled this line into another one it already paid.
CO-97 usually comes from bundling edits — the National Correct Coding Initiative (NCCI) edits, global surgical periods, or payer-specific bundling rules. Sometimes the bundling is right. Often it isn't: the two services were genuinely separate and distinct, and the claim just needed the right modifier or supporting documentation. That's why CO-97 is worth reviewing rather than writing off on sight.
CO-45 vs CO-97: the difference that decides your next move
Both codes share the CO group code — Contractual Obligation — so neither can be billed to the patient. But they point to different problems and different fixes.
- CO-45 is about price. You billed more than the contract allows. Fix: verify the allowed amount against your fee schedule; appeal only if it's underpriced.
- CO-97 is about bundling. The service was folded into another payment. Fix: confirm the services were separate, then resubmit with the correct modifier and documentation.
Get the distinction wrong and you either chase a legitimate write-off (wasting time on CO-45) or write off recoverable money (giving up on CO-97). The group code matters too: CO is provider responsibility, PR is patient responsibility, and OA is other adjustment. A balance that should have been PR but came back CO — or vice versa — is its own flag worth catching.
When these denials are recoverable vs a real write-off
Answer-first: CO-45 is usually a real write-off but sometimes an underpayment to appeal; CO-97 is frequently recoverable. Here's the decision:
Work the CO-97 when the bundled service was distinct — a separate site, session, or encounter — and the documentation supports it. A correct modifier 59 (or the more specific XE, XS, XP, XU modifiers) plus the note is often all it takes.
Appeal the CO-45 when the allowed amount is below your contracted rate. Pull your fee schedule, compare line by line, and submit it as evidence of underpayment.
Write it off when the CO-45 allowed amount matches your contract exactly, or the CO-97 bundling is genuinely correct under NCCI rules. Not every adjustment is a denial to fight — the skill is telling them apart at scale.
How to work a CO-97 denial step by step
- Read the remittance carefully — note which line was denied and which paid line it was bundled into.
- Check the edit — was this an NCCI bundling edit, a global-period edit, or a payer rule? That tells you which modifier or argument applies.
- Confirm the services were distinct in the documentation — different anatomical site, separate session, or unrelated procedure.
- Resubmit with the correct modifier and attach the supporting note, or file a corrected claim or appeal if the edit was simply wrong.
- Track the pattern — if the same CPT pairing keeps triggering CO-97, fix it upstream in coding rather than appealing one claim at a time.
Stop leaving denied claims on the table
The practices that recover the most aren't the ones that fight every denial — they're the ones that triage denials quickly and route each one to the right action. For the bigger picture on why denials are rising and how AI is changing the appeals workflow, see our guide to medical claim recovery and the analysis of AI-driven claim denials in 2026.
What does denial code CO-45 mean?
CO-45 means the amount you billed exceeds the payer’s allowed amount under your contract or fee schedule. The difference is a contractual write-off you cannot bill to the patient. It is an adjustment, not usually a denial you appeal — unless the allowed amount itself was calculated wrong.
What does denial code CO-97 mean?
CO-97 means the service is considered included in the payment for another service that was already paid, so it is not reimbursed separately. It often signals a bundling or global-period edit. Unlike CO-45, CO-97 is frequently recoverable when the second service was truly separate and distinct.
What is the difference between CO-45 and CO-97?
CO-45 is a pricing adjustment — you charged more than the contract allows. CO-97 is a bundling denial — the service was folded into another payment. CO-45 is usually a legitimate write-off; CO-97 is worth reviewing because a correct modifier or documentation can often get it paid.
Can you bill the patient for a CO-45 or CO-97 amount?
No. Both carry the CO (Contractual Obligation) group code, which means the amount is the provider’s responsibility under the payer contract. You cannot balance-bill the patient for a CO adjustment. Amounts that are patient responsibility carry the PR group code instead.
How do you appeal a CO-97 denial?
Confirm the two services were separate and distinct, then resubmit with the correct modifier — often modifier 59 or an XE/XS/XP/XU modifier — and documentation showing the distinct service. If the bundling edit was wrong, file a corrected claim or appeal with the operative or encounter note attached.
Is CO-45 always correct?
Not always. CO-45 is correct when the allowed amount matches your contract, but payers sometimes apply the wrong fee schedule or an outdated rate. Compare the allowed amount against your contracted rate; if it is short, appeal with your fee schedule as proof rather than writing it off.
What does the CO group code mean?
CO stands for Contractual Obligation. It marks adjustments the provider agreed to absorb under the payer contract, such as pricing write-offs (CO-45) and bundling (CO-97). It is different from PR (Patient Responsibility) and OA (Other Adjustment), which route the balance differently.
How much revenue do bundling denials cost practices?
It adds up quietly. CO-97 and similar bundling edits are among the most common adjustments on remittance advice, and a share of them are wrongly applied. Reviewing them systematically — rather than writing every one off — recovers revenue most practices leave on the table.
Turn denial codes into recovered revenue
ClaimRecover reads your remittance advice, flags which CO-97 and CO-45 lines are worth appealing, and drafts the appeal — so you stop writing off money you're owed.
See how ClaimRecover works →