You submitted what looked like a clean claim. Then the ERA comes back: CO-97, zero dollars paid. No plain-English explanation. Just a code and a denied line item.

CO-97 is one of the more confusing denials because it doesn't signal a missed authorization or a timely filing issue. It means the payer decided two services you billed count as one. That distinction matters, because the fix is completely different depending on the root cause.

This post explains what the CO-97 denial code means, why it shows up in therapy billing specifically, and how to resolve it — or appeal it — the right way.

What the CO-97 Denial Code Actually Means

The "CO" prefix stands for Contractual Obligation.[1] That means you cannot bill the patient for the denied amount. It's absorbed by the provider under the payer contract — this isn't a patient balance to collect.

The official definition: "The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated."[1]

In plain terms: the payer believes one of your billed codes is already covered by another code on the same claim. It won't pay for both.

CO-97 is enforced via NCCI edits — the National Correct Coding Initiative, a set of CMS-published rules that define which CPT code pairs can't be billed together without a qualifying modifier.[2] These edits exist across all of medicine, but they create specific friction points in behavioral health that are worth knowing upfront.

One thing worth clarifying early: CO-97 is not a duplicate claim denial, not a timely filing issue, and not an authorization denial. Those fall under different codes (CO-18 for duplicates, CO-29 for timely filing, CO-197 for authorization). If you're chasing the wrong fix, you'll waste time and miss the appeal window.

Why Behavioral Health Practices See CO-97 Denials

Most of the examples you'll find online involve surgical global periods or post-operative E&M bundling. That's not the world your practice lives in. Here's where CO-97 actually shows up in therapy billing.

Same-day individual and family therapy is the most common trigger. Billing 90837 (individual psychotherapy, 60 minutes) and 90847 (family psychotherapy with the patient present) on the same day, for the same patient, without a modifier will often generate a CO-97 on the second service. The payer sees two therapy sessions and bundles them together.

Psychotherapy add-on codes are another source of trouble. Codes like 90833, 90836, and 90838 — psychotherapy provided alongside an evaluation and management service — have specific pairing rules. Billing them with the wrong base code, or with a base code that the payer considers already inclusive, triggers CO-97.

Two similar codes on the same date can also flag. Consider the difference between 90834 and 90837: both are individual psychotherapy codes, just different time increments. If two clinicians in a group practice each see the same patient in the same day and each bill their respective code, the claim can look like bundling without clear documentation.

Payer-specific bundling policies add another layer. Some commercial plans and Minnesota Medicaid programs go beyond NCCI with their own proprietary edits. What clears with one payer may deny with another, which makes blanket assumptions risky.

Not every CO-97 is an error, either. Sometimes the payer is right: a code genuinely is included in another. The first step is always verifying before you resubmit or appeal.

Step-by-Step: How to Fix a CO-97 Denial

Step 1: Read the ERA carefully. CO-97 often appears alongside a remark code that gives more context about which service was bundled — the specific code varies by payer, so read the full ERA line, not just the CARC. Note exactly which service line was denied and the reason code attached to it.

Step 2: Look up the NCCI edit. CMS publishes NCCI edit tables publicly. Look up the code pair and check the modifier indicator.[2] This is the critical number:

Indicator 1: A modifier may override the edit, provided clinical documentation supports distinct services
Indicator 0: No modifier is allowed — this bundling cannot be overridden regardless of what you append

Step 3: Determine whether Modifier 59 applies. If the modifier indicator is 1, and the services were genuinely distinct — different time, different clinical purpose, or different treating clinician — Modifier 59 (or the more specific X modifiers: XE, XS, XP, XU) may allow separate billing.[3] Review documentation before you add the modifier. Don't use it to override an edit without clinical justification.

Step 4: Resubmit with the modifier and supporting notes. Attach progress notes that demonstrate the services were separate and medically necessary. Time-stamped session notes, distinct treatment goals for each service, and clear documentation of who provided what and when are your evidence.

Step 5: Appeal when a modifier isn't allowed. If the modifier indicator is 0, resubmission won't work — the payer won't pay regardless of what's appended. Write an appeal letter citing the clinical necessity of both services, the distinct nature of each, and any relevant payer contract language.

An example of how this plays out: a group practice in St. Paul bills 90847 (family therapy) the same day as 90837 (individual therapy) for the same patient. The payer returns CO-97 on the family session. The therapist's notes document the individual session ended at 2:00 pm and the family session began at 3:00 pm with a separate treatment focus. Modifier 59 is appended, notes are attached, the claim is resubmitted — and it's paid.

A Note on Modifier 59 and Compliance

Modifier 59 is a legitimate tool, but it's also one that attracts scrutiny. The Office of Inspector General actively reviews modifier 59 usage patterns and has flagged outlier providers for audit.[3]

Appending Modifier 59 to bypass an edit without documentation to back it up isn't just a billing error — it's the kind of practice that can trigger a broader audit of your claims history. The modifier signals to the payer: "these services were distinct." Your documentation has to actually prove that.

If you're regularly billing same-day services in your practice, make sure the clinical notes are doing the work. The modifier is only as strong as what's behind it.

When to Appeal Instead of Rebill

If the NCCI modifier indicator is 0, you can't solve this with a modifier. The path forward is an appeal, not a resubmission.

Payer-specific bundling edits — the proprietary rules that go beyond NCCI — are sometimes more vulnerable to appeal. If the bundling rule isn't CMS-mandated, you have more ground to challenge it. A well-documented appeal letter citing the clinical necessity of each service, the distinct session times, and your payer contract terms can overturn these.

An Illinois group practice that receives CO-97 on a payer-specific edit (not in the NCCI tables) and submits an appeal with separate progress notes and a contract citation has a reasonable shot at reversal. These aren't guaranteed wins, but they're worth pursuing rather than writing off the revenue.

One thing to watch: appeal deadlines. Missing the appeal window forfeits the revenue just as surely as ignoring the denial. Good denial tracking means logging appeal deadlines separately from claim submission deadlines, so nothing slips through.

How to Prevent CO-97 Denials Before You Submit

The most efficient fix is the one that happens before the claim goes out.

Build a same-day service protocol. If your practice regularly bills same-day individual and family therapy billing services, create a standard pre-submission checklist. Is Modifier 59 needed? Is documentation in place? Don't leave it to judgment on a claim-by-claim basis.

Use a claim scrubber. Good billing software or a billing service flags NCCI conflicts before the claim leaves your system. A bundling conflict caught before submission takes minutes to fix. The same conflict caught post-denial can take weeks to resolve and may still not recover the full amount.

Document same-day services separately. Time-stamp sessions, write distinct progress notes for each service, and make the clinical purpose of each session clear. That documentation is both your defense in an audit and your evidence in an appeal.

Know your payer mix. In Minnesota, payers like UCare, Medica, and Minnesota Medicaid each have their own bundling policies layered on top of NCCI. What works with one doesn't always work with another. Your billing team should have a payer-by-payer reference, not just a copy of the NCCI tables.

Run a monthly denial trend review. If CO-97 keeps appearing on the same code pair, you have a systemic issue — not a one-off. A recurring bundling denial is better caught in an A/R review than discovered six months later when the pattern has cost you thousands. Tracking your denial rate calculation over time is one way to surface these trends early.

Final Thoughts

CO-97 doesn't mean your care wasn't legitimate. It means the payer thinks two services you billed were one. In behavioral health, that most often happens when same-day services are billed without the right modifier and the documentation to support it.

Fixing it correctly takes knowing which code pairs trigger bundling edits, which payers allow modifier overrides, and how to write an appeal that actually gets read. That's the work BreezyBilling does every day: catching bundling conflicts before submission, resolving CO-97 denials when they come through, and flagging recurring patterns in monthly A/R reviews so the same issue doesn't quietly drain revenue month after month.

If CO-97 denials are showing up repeatedly in your A/R, that pattern is costing you money. BreezyBilling is here to help.

Sources

Claim Adjustment Reason Codes — X12, 2026
National Correct Coding Initiative (NCCI) Edits — Centers for Medicare & Medicaid Services, 2026
Use of Modifier 59 to Bypass Medicare's National Correct Coding Initiative Edits — Office of Inspector General, HHS; and Medicare NCCI Policy Manual — CMS

CO-97 Denial Code: What It Means and How to Fix It in Behavioral Health Billing