CO 29 denial code

Claim adjustment reason code 29. Often reported as CO 29.

Timely filing limit has passed

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 29 means

The payer received the claim after its filing deadline for the date of service, so it would not pay.

Every payer sets a time limit for submitting claims, and this code means the payer counted the claim as late. It is usually CO, which means the provider normally cannot bill the patient for it.

The denial can often be overturned if you can show the claim was sent on time, for example with a clearinghouse acceptance report, or that the delay was caused by another payer's processing. Deadlines and accepted proof vary by payer and contract.

Group codes seen with 29

On a remittance, 29 comes after a group code. These are the ones it is most often reported with:

• CO 29 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The claim was sent for the first time after the payer's filing limit.
• An earlier claim was rejected at the clearinghouse or payer and nobody followed up.
• The claim was first sent to the wrong payer and reached the right one too late.
• A corrected claim or secondary claim was sent after the payer's deadline for those submissions.

What to do next

1. Find proof of the original timely submission, such as a payer acceptance report or a clearinghouse acceptance report.
2. Appeal with that proof and a short timeline of submissions.
3. If the delay came from another payer's processing, include that payer's remittance or denial with dates.
4. Check your contract for any timely filing exceptions before writing anything off.
5. Add a rejection worklist so unaccepted claims are fixed long before the deadline.

Related codes

• 16 (reason code) Missing information or billing error
• 18 (reason code) Exact duplicate claim or service
• 27 (reason code) Service after coverage ended