CO-109 means you sent the claim to the wrong place. The patient may have a Medicare Advantage plan instead of original Medicare, the service may belong to a different Medicare contractor (such as the DME MAC), or another plan handles that benefit. Find the right payer and send it there.
The official wording
The X12 Claim Adjustment Reason Code list defines 109 as: "Claim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contractor."
The letters in front are the group code. CO means contractual obligation (the provider absorbs it), PR means patient responsibility, and OA is other adjustment. The same reason code can come with different group codes, so always read both.
Common causes
- Medicare Advantage patient billed to original Medicare.
- DME, prosthetics or supplies billed to the Part B contractor instead of the DME MAC.
- A carved-out benefit, such as behavioral health, lab or radiology managed by a separate company.
- The patient's Medicaid is a managed care plan, not fee-for-service.
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How to fix it
- Check eligibility for Medicare Advantage enrollment, carve-outs or the plan's vendor.
- Send the claim to the right payer as a new claim.
- Keep the CO-109 remittance. If the correct payer's deadline is close, the first denial may help show you filed in good faith.
Remark codes that come with CO-109
| Remark code | Official wording | What to do |
|---|---|---|
| N418 | "Misrouted claim. See the payer's claim submission instructions." | Check the payer's claim submission instructions and the patient's ID card, then send the claim to the right payer or address. |
| N104 | "This claim/service is not payable under our claims jurisdiction area." | For Medicare, find the right contractor for that state or service type (DME, home health, Part A or Part B) and send it there. |
A CO-109 example
| Line on the remittance | Amount | What it means |
|---|---|---|
| Billed charge | $180.00 | Office visit |
| CO-109 with N104 | $180.00 | Sent to the wrong Medicare contractor |
| Paid by payer | $0.00 | Nothing paid |
Nothing here is lost yet. The claim went to the wrong place. Send a new claim to the right payer, and keep this denial: it shows you filed on time.
Common CO-109 situations
| What happened | Where the claim should go |
|---|---|
| A Medicare Advantage patient was billed to traditional Medicare | The Medicare Advantage plan on the ID card |
| A Medicaid managed care patient was billed to state Medicaid | The managed care plan |
| A behavioral health service under a carved-out plan | The behavioral health company named on the card |
| Durable medical equipment sent to the Part B contractor | The DME Medicare contractor (DME MAC) |
| The patient moved, or the claim went to the wrong state Blue plan | The plan for the patient's home state or the local plan, per the card |
How to post CO-109
- Post the zero payment and leave the balance open.
- Update the patient's insurance on file to the right payer.
- Send a new claim (not a corrected claim) to the right payer.
- Save the CO-109 remittance as proof of timely filing.
CO-109 checklist
- ☐ You checked both sides of the ID card.
- ☐ You ran eligibility with the payer you think is right.
- ☐ You used the right payer ID in your clearinghouse.
- ☐ The timely filing clock of the new payer is still open.
Questions people ask about CO-109
Does CO-109 stop the timely filing clock?
No. The correct payer's own deadline still applies. Refile quickly. Our timely filing calculator shows the last day.
Can I bill the patient for CO-109?
No. The claim just went to the wrong payer.
Is CO-109 a timely filing risk?
Yes. The right payer's clock started on the date of service. Send the new claim quickly and keep the CO-109 denial as proof you filed on time somewhere.
Should I appeal a CO-109?
Usually no. The fix is to send the claim to the right payer, not to argue with the wrong one.
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PR-1 · PR-2 · PR-3 · CO-4 · CO-5 · CO-11 · CO-15 · CO-16 · OA-18 · CO-22 · OA-23 · CO-24 · CO-26 · CO-27 · CO-29 · CO-31 · CO-45 · CO-49 · CO-50 · CO-59 · PR-96 · CO-97 · CO-109 · CO-119 · CO-129 · CO-140 · CO-146 · CO-151 · CO-167 · CO-170 · CO-181 · CO-185 · CO-197 · CO-198 · PR-204 · CO-234 · CO-236 · CO-242 · CO-252 · CO-253 · CO-288 · CO-A1 · CO-B7 · MA130 · N130 · N23 · N290
Timely filing limits by payer: Cigna timely filing limit · HealthSpring timely filing limit · Aetna timely filing limit · UnitedHealthcare timely filing limit · Humana timely filing limit · corrected claim timely filing limits
Sources: X12 Claim Adjustment Reason Code list (109), read October 12, 2026; CMS Medicare guidance where Medicare rules are mentioned. Last reviewed October 26, 2026. General information, not coding or legal advice. Payer rules differ, so check the remark code and the payer's own policy. Remark code wording from the X12 RARC list as published by claim.md, read October 26, 2026.