CO-24 means the service is paid through a capitation arrangement, a fixed monthly payment to a medical group or provider, so this claim is not paid fee-for-service. Either your practice is already paid through capitation, or the claim belongs with the medical group or IPA that holds the contract.
The official wording
The X12 Claim Adjustment Reason Code list defines 24 as: "Charges are covered under a capitation agreement/managed care plan."
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.
What CO-24 is telling you
Under capitation, a payer pays a set amount per member per month to a provider or medical group, which then covers certain services. When a claim comes in for one of those services, the payer adjusts it with CO-24 because the payment already went out another way.
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Common causes
- The patient's HMO or Medicare Advantage plan assigns them to a medical group or IPA, and that group should be billed.
- Your practice is capitated for this service and the claim is for encounter reporting only.
- The patient's assigned primary care provider is someone else and the payer's records were not updated.
How to fix it
- Check the member card and eligibility for a medical group, IPA or assigned PCP.
- If a group holds the risk, bill the group under its claims rules.
- If your practice is capitated, the claim is an encounter. Post the CO-24 as a contractual adjustment.
- If the patient's PCP assignment is wrong, have the patient update it, then ask for reprocessing.
The most common CO-24: Medicare Advantage
Most CO-24 denials billers see come from Original Medicare. The patient joined a Medicare Advantage plan, the claim went to the Medicare contractor anyway, and Medicare says the plan is responsible.
| Line on the remittance | Amount | What it means |
|---|---|---|
| Billed charge | $180.00 | Office visit billed to Original Medicare |
| CO-24 | $180.00 | Patient is in a Medicare Advantage plan on this date |
| Paid by Medicare | $0.00 | Bill the Advantage plan instead |
Check eligibility. If the patient was in the plan on the date of service, send the claim to the Advantage plan. If Medicare's records are wrong, the patient needs to fix their enrollment, then you submit again.
When Original Medicare still pays
Some services stay with Original Medicare even for Advantage members. Those claims need the right modifier, or Medicare will deny them with CO-24.
| Situation | Modifier | Meaning |
|---|---|---|
| Patient elected hospice, you are the attending physician not paid by the hospice | GV | Attending physician not employed or paid under arrangement by the hospice |
| Patient elected hospice, care not related to the terminal condition | GW | Service not related to the hospice patient's terminal condition |
| Patient is in an approved clinical trial, investigational service | Q0 | Investigational clinical service in an approved study |
| Patient is in an approved clinical trial, routine service | Q1 | Routine clinical service in an approved study |
If the filing limit has passed and you only need to add one of these modifiers, ask for a reopening instead of sending a new claim.
Commercial HMO cases
- Delegated medical group or IPA. The HMO pays the group a set amount per member. Claims go to the group, not the HMO. The group's name is usually on the member card.
- Your practice is the capitated PCP. Your visits are already paid through the monthly capitation check. The claim is an encounter record. Post CO-24 as a contractual adjustment.
- Wrong PCP on file. The patient picked you but the plan still lists someone else. The patient must change the PCP with the plan, then you ask for reprocessing.
CO-24 checklist
- ☐ Eligibility shows whether the patient had a Medicare Advantage or HMO plan on the date of service.
- ☐ You know if a medical group or IPA holds the risk for this patient.
- ☐ Hospice and clinical trial claims have the right modifier.
- ☐ Encounter claims under your own capitation are posted as contractual adjustments.
- ☐ The patient is not billed for the CO-24 amount.
Questions people ask about CO-24
Can I bill the patient for CO-24?
No. The service is covered through the capitation arrangement.
Where do I send the claim instead?
To the medical group or IPA listed on the patient's card or in the eligibility response, following that group's claim rules.
Why did Original Medicare deny my claim with CO-24?
The patient was enrolled in a Medicare Advantage plan on the date of service. Send the claim to that plan, or if the enrollment was wrong, have the patient fix it and submit again.
Which modifiers let Original Medicare pay for an Advantage patient?
GV or GW for hospice patients, and Q0 or Q1 for approved clinical trials, when the service qualifies.
Is CO-24 a denial if my practice is capitated?
Not really. Your payment for that service came through the monthly capitation check. The claim is an encounter record, and the CO-24 is a contractual adjustment.
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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 (24), read October 27, 2026; CMS Medicare guidance where Medicare rules are mentioned; Noridian Medicare JE Part B reason code guidance, "Medicare Advantage Plan" (CO-24), read October 27, 2026. Last reviewed October 27, 2026. General information, not coding or legal advice. Payer rules differ, so check the remark code and the payer's own policy.