CO P31 denial code

Claim adjustment reason code P31. Often reported as CO P31.

Exacerbation denied: time limit exceeded

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 P31 means

On a property and casualty claim, care for a flare up was denied because treatment went beyond the time allowed.

You will see it only on property and casualty remittances, for example from a workers' compensation or auto carrier. Payers and jurisdictions often limit how long treatment for an exacerbation may last. P31 means the dates billed went past that limit.

Further care may need a new request or authorization, depending on the jurisdiction's rules.

Group codes seen with P31

On a remittance, P31 comes after a group code. These are the ones it is most often reported with:

• CO P31 (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

• Treatment continued past the period allowed for the exacerbation.
• No extension was requested before the period ended.
• Dates of service were wrong on the claim.

What to do next

1. Check the time limit that applies to exacerbation treatment for the claim.
2. Request an extension or authorization for ongoing care with clinical support.
3. Correct any wrong dates and resubmit.

Related codes

• P30 (reason code) Flare up denied: incomplete records
• P15 (reason code) Outside workers' comp treatment guidelines