CO-27 means "Expenses incurred after coverage terminated." The payer is telling you the patient's insurance had already ended before the date of service, so the claim sits outside covered benefits. The tricky part: CO-27 is sometimes correct and sometimes a payer data error. Which situation you are dealing with determines whether there is money to recover and from whom.
What CO-27 means
The full CARC definition is "Expenses incurred after coverage terminated." Two distinct situations produce the same code:
- Coverage genuinely ended. The patient's employer dropped their plan, a marketplace policy lapsed for non-payment, or COBRA was never elected.
- The payer's records are wrong. The termination date in the insurer's system is incorrect and the patient was actually enrolled on the date of service.
Those two situations call for completely different responses. A coverage verification call before doing anything else saves time and prevents writing off a balance that was actually collectible.
CO-27 vs. PR-27: who absorbs the balance?
The group-code prefix on the 835/ERA line decides responsibility. CO-27 is a contractual obligation, meaning the provider must write off the balance and cannot bill the patient. PR-27 shifts the balance to patient responsibility and the patient can be billed. Payers do not always post the correct group code, so confirm the prefix before sending any patient statement or making a write-off entry.
When CO-27 is recoverable
Several scenarios leave room for appeal or corrected patient billing.
- Wrong termination date in the payer's system. Call the payer's member services line, ask for the coverage start and end dates, and document the representative's name, call time, and what they confirmed. If coverage was active on the DOS, submit a corrected claim with a coverage verification letter and a clear note explaining the discrepancy. This is the most straightforward recovery path and succeeds regularly when the payer's records are simply wrong.
- ACA marketplace grace period. Under federal ACA rules, marketplace plans are required to pay claims during the first 30 days of a premium grace period for non-payment. Claims delivered in days 31 to 90 may be pended. If the subscriber pays back premiums before the grace period expires, coverage is reinstated retroactively and those pended claims must be processed. A CO-27 on a marketplace plan claim is worth a follow-up call to ask whether the patient caught up on premiums before writing it off.
- COBRA election window. After a qualifying event (job loss, reduction in hours, divorce), a patient has up to 60 days to elect COBRA coverage. If they elect within the window and pay back premiums, coverage is reinstated from the qualifying event date. A CO-27 denial on a claim delivered during the election window may become payable after a COBRA election, so checking patient status with the plan administrator before final write-off is worthwhile.
- Retroactive termination with patient responsibility. When an employer retroactively terminates coverage after the fact (the patient was enrolled on the DOS but was terminated retroactively), the balance typically shifts to patient responsibility, not a provider write-off. The patient received services under coverage that was later revoked; the practice can collect from the patient. Confirm this is PR-27 territory before billing.
How to work a CO-27 denial
The question is purely factual: was coverage in force on the date of service? The workflow is short.
- Pull the 835 line and note the group code (CO or PR) and the exact termination date the payer used to deny.
- Call the payer's member services line and ask for coverage dates. Document who you spoke with, when, and the confirmed dates.
- Cross-reference with the patient: insurance card, employer HR documents, COBRA election letter, or marketplace plan ID.
- If coverage was active per the payer's own records, request a reprocess or submit a corrected claim with the coverage verification letter attached and the error documented in the appeal narrative.
- If coverage had genuinely ended, confirm whether the balance is CO or PR, then either write off (CO-27) or send a patient statement (PR-27) with a clear explanation of the coverage gap.
Watch for cluster patterns
CO-27 denials are worth tracking by payer and employer group, not just individually. A spike from a single employer group within a short date range usually signals a group termination or open-enrollment change that affects multiple patients at once, not a string of isolated individual lapses. Identifying the cluster early means one outreach call to the employer's HR administrator can resolve a batch of denials rather than working each claim separately.
For practices with high-volume employer groups on self-insured plans, the common billing errors guide covers additional coverage-related denial patterns that travel with CO-27.
Prevention: verify at check-in, not just at scheduling
CO-27 is almost always a verification gap. Practices that confirm coverage once at pre-registration and not again at check-in miss same-day terminations, month-end plan changes, and late premium lapses that happen between scheduling and the visit. Real-time eligibility verification on the day of service is the reliable fix. Keep the verification response with a timestamp in the patient record. If a CO-27 denial arrives later, that timestamped response is your evidence that coverage appeared active at the point of service, which supports an appeal based on payer data error.
See the revenue leakage guide for how CO-27 write-offs compound into systematic revenue loss when they are never audited by group code, and the CO-29 guide for the related timely-filing issue that surfaces when CO-27 appeals take time and the filing deadline approaches.