Denial Code Decoder
CO-27 — Coverage had already ended
The patient's coverage under this plan had terminated before the date of service. It is the eligibility failure that hurts most, because nothing on the day of the visit looks wrong — the card is real, the patient believes they are covered, and the termination is only visible in the payer's file. It is also the one most often reversed, because terminations are entered retroactively and are sometimes entered in error.
Billable to the patient? Frequently yes, once the termination is confirmed and the correct payer has been ruled out — but confirm the date before billing anyone, because a retroactive termination that is later reversed leaves you having statemented a covered patient.
Where this denial is born
- Front desk
- Coding
- Claim build
- Submission
- Adjudication
This denial is usually created at the highlighted stage — that is where prevention lives.
Answer the questions — follow the path
The same questions an experienced biller asks, in order. Your answers draw the route to the right action.
Does an eligibility check confirm the coverage ended before the date of service?
Ask for the coverage period, not just active or inactive — the answer you need is a date range that either contains the service or does not.
The full decision tree
Does an eligibility check confirm the coverage ended before the date of service?
Ask for the coverage period, not just active or inactive — the answer you need is a date range that either contains the service or does not.
- Yes →
Does the patient have other coverage that was active that day?
A termination is usually a change, not an ending — a new employer plan, a move to Medicaid or Medicare, a spouse's plan.
- Yes →
Bill the plan that was actually in force. Submit to the correct payer, and mind its filing limit — that clock has been running since the date of service, not since this denial.
- No →
Move the balance, and tighten re-verification. With no coverage in force the balance is generally the patient's. Tell them what the payer said and when the coverage ended, then find why the visit was not re-verified.
- Yes →
- No →
Dispute the termination date. Send the eligibility response showing coverage in force on the date of service and ask for reprocessing. Keep the response — a verification captured on the day is the evidence this argument runs on.
Prevention
Re-verify coverage close to every date of service rather than trusting the record from the last visit. An eligibility response states the coverage period; a card states nothing about today.
Related reading
The code list, and when it was last checked
X12 maintains the Claim Adjustment Reason Codes list, where this code is listed as 27. The list carries the number alone: the CO in front of it is the adjustment group the payer chose for this line, which decides who owes the balance, and the same code can arrive under a different group from a different payer. It has been on the list since January 1, 1995.
Checked against the list revision dated November 1, 2025 on August 7, 2026, where it reads as an active code.
Sources
The paragraphs behind the guidance above. A page that tells you what to do about money should show you what the instruction rests on.
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