CO-45
Depends on the detailsCharge exceeds the fee schedule or allowed amount
Group CO — Contractual Obligation — an adjustment tied to the contract between the insurer and the provider. You usually cannot be billed for a CO amount.
CO-45 means the provider billed more than the plan's fee schedule or maximum allowable amount, and the difference is being adjusted off. This is normal and expected for in-network care — the provider agreed by contract to accept the plan's allowed amount.
Because it's a Contractual Obligation (CO), you should not be billed for the CO-45 amount. It isn't a denial of your care; it's the contractual write-off between the provider and the plan.
Got a CO-45 denial? Our free generator can draft a ready-to-send appeal letter for this denial in a few minutes. Start your appeal →
Why you're seeing CO-45
- The provider's list price is higher than the plan's negotiated rate (normal for in-network care).
- The service has a set fee-schedule maximum the plan pays.
- The provider billed a standard rate rather than the contracted rate.
Can you appeal it?
Usually nothing to appeal — but do dispute it if a provider tries to balance-bill you for the written-off amount.
What to do next
- 1Confirm you're not being billed for the CO-45 amount — you shouldn't be for in-network care.
- 2If the provider bills you the difference (balance billing), dispute it and cite the CO-45 write-off.
- 3Verify the provider was correctly treated as in-network if the allowed amount looks too low.
Evidence that helps
- The EOB showing the CO-45 adjustment and the plan's allowed amount.
- Your provider's network status for the date of service.
Frequently asked questions
Do I owe the CO-45 amount?
No. CO-45 is a contractual write-off between the provider and the plan. For in-network care you should not be billed for it. If you are, that may be improper balance billing you can dispute.
Is CO-45 a denial?
Not really — it's a pricing adjustment, not a denial of your care. The claim is still being paid at the plan's allowed rate; the amount above that rate is simply written off.
Write your appeal now
Generate a tailored appeal letter, escalation letter, and phone script — free, private, and entirely in your browser.
Other common denial codes
Last reviewed July 18, 2026. Denial-code lists (CARC/RARC) are updated three times a year; we review these explanations against the current list.
Sources & references
These explanations are written in plain language and based on the authoritative sources below. Always confirm the specifics against your own plan documents and denial letter.
- ASC X12 — Claim Adjustment Reason Codes (CARC)
The standards body that maintains the official CARC list (the CO/PR codes), updated three times a year.
- CMS / X12 — Remittance Advice Remark Codes (RARC)
The remark codes (N-/M- codes) that accompany a CARC and give the specific reason for an adjustment.
- HealthCare.gov — Appealing a health plan decision
Official overview of internal appeals and external review rights for Marketplace and most private plans.
- Your state's insurance regulator
State agencies enforce external review and consumer protections; find yours via the NAIC directory.
Important: this is not legal or medical advice.
AppealBrain is a free, self-help tool that helps you draft an appeal letter using the information you provide. We are not a law firm, medical provider, or insurance company, and using this tool does not create an attorney–client relationship. Appeal rules and deadlines vary by plan and state — always review your own denial letter and plan documents, and consider consulting a licensed professional for your specific situation. We do not guarantee any outcome.