What does CO-45 mean?

CO-45 is a Contractual Obligation (CO) denial: "Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement." Your billed charge was higher than the payer's allowed/contracted amount — the difference is a contractual write-off, not a real denial.

CO · Contractual ObligationCARC 45

Denial Code CO-45

Q: Is CO-45 the patient's responsibility or a provider write-off?

CO-45 carries the CO group code (Contractual Obligation): Provider/contractual responsibility — not billable to the patient while denied. A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.

Source: X12 Claim Adjustment Reason Codes (CARC) & Group Codes. Maintained by the D3rx Clinical Billing Team.

What CO-45 means

Your billed charge was higher than the payer's allowed/contracted amount — the difference is a contractual write-off, not a real denial.

Seeing this on your remittance?

CO-45 is a contractual write-off — but verify you're not being underpaid

Check for underpayment Ask D3 about CO-45

Routine CO-45 is written off, never billed to the patient. The real risk is a payer paying below your contracted rate — check it free.

CO group code: who absorbs the charge

Contractual Obligation — Provider/contractual responsibility — not billable to the patient while denied.

A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Why CO-45 happens

The practice's standard charge is set above the payer's fee schedule (normal and expected)
The contracted in-network allowed amount is lower than billed charges
The line was priced to the maximum allowable under a legislated or negotiated fee arrangement
An out-of-network allowable was applied where a higher in-network rate was expected

What to do when you get CO-45

1Confirm the CO-45 amount equals (billed charge − allowed amount) — it should reconcile exactly
2Verify the payment posted matches your contracted fee schedule for that code
3Write off the CO-45 amount to contractual adjustment; do NOT bill it to the patient
4If the allowed amount looks lower than your contract, pull the contract and dispute the underpayment

Appeal, correct, or write off CO-45?

In the normal case CO-45 needs no action at all — it is the contractual difference between what you charge and what the contract allows, and under a CO (contractual obligation) group code it must be written off, never billed to the patient. The only time to push back is a suspected underpayment: if the allowed amount is below your contracted rate, that is a contract/payment dispute (often via a reopening or payment-review request), not a standard appeal. Compare every CO-45 against your fee schedule to catch payers defaulting to a lower rate.

Timing & deadlines

No filing deadline applies to a routine write-off. For a suspected underpayment dispute, follow the payer's payment-reconsideration window (commonly ~90-180 days from the remittance for commercial plans; Medicare reopenings are generally available within 12 months of the remittance for clerical-type corrections).

Example

A practice bills 99214 at $200. The contracted allowed amount is $130, so the payer pays its share of $130 and reports a $70 CO-45 adjustment. The $70 is a contractual write-off — correct and expected. If instead only $90 were allowed when the contract says $130, that $40 gap is an underpayment to dispute.

Prevent CO-45 going forward

Load every payer fee schedule into your PM system and auto-compare on posting
Run monthly underpayment reports comparing paid vs. contracted amounts
Re-load fee schedules promptly after each contract update
Flag any code where the allowed amount drops unexpectedly between remittances

Code families most affected

Every fee-for-service code billed above the contracted rate
Evaluation & Management and procedures alike
Out-of-network claims priced to an allowable

Related codes

Denial codes you'll often see alongside CO-45

CO-97 OA-23 PR-1

Payer notes

CO-45 is one of the most common adjustments on any remittance and is informational in the routine case. Per X12, the CO-45 amount cannot equal the entire charge and should not duplicate prior-payer adjustments. The real value is using it as an audit signal: a CO-45 larger than your expected contractual difference is the fingerprint of a fee-schedule or contract-loading error.

Make sure CO-45 isn't a hidden underpayment

Routine CO-45 is a contractual write-off — but a payer paying below your contracted rate looks identical on the remittance. Run a free underpayment check before you adjust it off.

Check for underpayment Ask D3 about CO-45 All denial codes

Medical billing disclaimer

CARC/RARC definitions are the standardized X12 set; group-code semantics follow the X12 Claim Adjustment Group Code standard. Filing and appeal windows vary by payer — the standard anchors shown (Medicare redetermination 120 days from the remittance; Medicare timely filing 12 months from date of service; most commercial payers ~90-180 days) are general references, not a guarantee for any specific plan. Always confirm the rule in the payer's provider manual before acting. D3rx is not responsible for claim outcomes.