Short answerCO-45 means the charge exceeds the fee schedule, maximum allowable or contracted amount; the CO group code means the difference is the provider's contractual obligation, not the patient's. It is correct when the payer allowed the contracted rate, and an underpayment when it allowed less.
CO-45 is one of the most common adjustment codes on any remittance. Most practices post it automatically. That's where underpayments slip through.
What CO-45 means
- CO: contractual obligation; the amount can't be billed to the patient.
- 45: charge exceeds the fee schedule, maximum allowable or contracted/legislated fee arrangement.
When it's correct
Your charge is $1,000, the contract allows $620, the payer allows $620. The $380 CO-45 adjustment is a normal write-off.
When it hides an underpayment
| Charge | Contracted rate | Allowed | CO-45 | Problem |
|---|---|---|---|---|
| $1,000 | $620 | $620 | $380 | None |
| $1,000 | $620 | $540 | $460 | $80 underpaid, hidden in CO-45 |
How to catch it
Compare the allowed amount, not just the adjustment, with your contract. Automating that comparison is the fastest way, see AI underpayment detection.
This article is general billing information, not legal or coding-compliance advice. Payer rules, CPT descriptors and federal guidance change; check the current versions for your claims.