CO 110 denial code

Claim adjustment reason code 110. Often reported as CO 110.

Billed before the date of service

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 110 means

The claim was rejected because the billing date is earlier than the date the service was provided.

The payer saw a claim that was billed before the service happened. That usually means a date error, or a claim for a future service or rental period sent too early.

It is a data problem rather than a coverage problem, so correcting the dates normally fixes it.

Group codes seen with 110

On a remittance, 110 comes after a group code. These are the ones it is most often reported with:

• CO 110 (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 date of service was keyed wrong, such as a future date or a transposed month.
• A recurring rental or supply claim was sent before the period started.
• The claim was created and sent before a scheduled service took place.

What to do next

1. Check the date of service against the medical record and the appointment history.
2. Correct the dates and submit a new claim if the service was actually provided.
3. Hold recurring claims until the service or rental period has begun.

Related codes

• 16 (reason code) Missing information or billing error