CO-26: expenses incurred prior to coverage.

What X12 says CARC 26 means

Expenses incurred prior to coverage.

CARC 26 · Start 01/01/1995.

In plain terms: The expense was incurred before the patient's coverage began.

What it means on a remittance

The payer compared the date of service with the effective date on its eligibility file and found that the service came first. Its sibling, CARC 27, covers expenses incurred after coverage terminated. Retired CARC 28 was marked by X12 as redundant to codes 26 and 27.

Typical causes

• The patient’s coverage began after the date of service.
• Eligibility was checked for a date other than the date of service.
• The patient had a different plan on that date and the claim named the new one.
• A waiting period or late enrollment pushed the effective date past the visit.

These are common billing patterns, not a diagnosis of your claim. The remittance and the payer's policy decide.

What to check

1. Run an eligibility check for the date of service and note the effective date.
2. Ask the patient who covered them on that date.
3. Check the payer name and member ID on the claim.
4. Note the filing deadline for the payer you now have to bill.

Correct, resubmit or appeal

If the effective date is right, bill the plan that covered the patient on the date of service, or follow your policy for self-pay. If the payer’s date is wrong, send proof of coverage and ask for reprocessing.

Medicare dates that apply

A Medicare redetermination request must be filed within 120 calendar days from the date a party receives the notice of the initial determination; receipt is presumed 5 calendar days after the notice date unless there is evidence to the contrary (42 CFR 405.942(a)), and a late request can be considered for good cause (405.942(b)). Other payers set their own appeal windows in the contract or plan documents, so read the notice for the date. The tool above runs the date math.

Related codes

X12 does not publish a table that pairs each code with remark codes; the payer picks the remark code and prints it beside the CARC on the same remittance line.

Other codes: CARC 27 (expenses after coverage ended), CARC 31 (patient not identified as insured) and the full lookup.

Worked example (hypothetical)

A claim for a March 3 visit denies with CO-26. Eligibility shows the patient’s plan began March 15. The patient says the earlier plan was through a prior employer. The biller bills that plan.

Sources

• X12: Claim Adjustment Reason Codes — code text, usage notes and dates (list dated 10/30/2026, retrieved 2026-11-02)
• 42 CFR 405.942 — eCFR, current through 2026-10-29 (retrieved 2026-11-02)

Code descriptions are X12 copyrighted material, quoted here only for the codes on this page and linked to the owner. For the full lists, use X12. The X12 text and the Medicare rule above were read from these pages on November 2, 2026. Causes, checks and examples are general billing practice written for this page, not X12 content. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.