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CO-26: Expenses Incurred Prior to Coverage

The payer says the patient's plan had not started yet on the date of service. Most CO-26 denials are fixed by finding the right payer for that date, not by appealing.

What Does CO-26 Mean?

Claim adjustment reason code 26 reads: "Expenses incurred prior to coverage." The payer is telling you the date of service falls before the patient's start date with that plan. In plain words, the patient was not yet a member on the day of the visit.

It is the mirror image of CO-27, which means the coverage had already ended. Both denials have the same root cause: the claim went to a plan that did not cover the patient on that date.

	CO-26 at a glance
Official text	Expenses incurred prior to coverage
Usual group code	PR is most common. Some payers send CO or OA
Who usually pays	The plan that covered the patient on that date, or the patient if no plan did
Can you appeal?	Only when the payer's start date is wrong
Fastest fix	A fresh eligibility check for the exact date of service

A note on the group code

You will see code 26 paired with PR, CO or OA. PR-26 is the most common, because the payer is pointing to the patient when no other coverage applies. X12, the group that maintains these codes, has said that pairing CO with code 26 makes little sense, since a contract cannot require a write-off for care given before the contract existed. So a CO-26 alone does not prove you must write the balance off. Check your contract and who covered the patient that day.

Why CO-26 Happens

A new job plan that has not started yet. Many employer plans start on the first of the month after a waiting period. The patient may have a card before the plan is active.
New Medicare Part B. If someone signs up during the General Enrollment Period, Part B starts the month after they sign up. Visits before that month deny.
An annual wellness visit billed too early. Medicare does not cover the wellness visit (G0438) in the first 12 months of Part B. CMS told its contractors to deny these claims with reason code 26, remark code N130 and group code PR.
A newborn not yet added to the plan. Under federal special enrollment rules, a baby added to an employer plan within 30 days is covered from birth. Claims sent before the baby is added will deny until the plan updates its records.
Medicaid approved after the visit. Medicaid can pay for some months before the approval, but claims deny until the eligibility system shows the earlier start date.
The wrong card on file. The patient gave you a card for a new plan, but the visit happened before it started. The old plan may still owe the claim.

How to Fix a CO-26 Denial, Step by Step

Run a new eligibility check for the exact date of service. Look at the coverage start date and compare it with the date on the remittance.
Ask the patient what coverage they had that day. Think old employer plan, COBRA, a spouse's plan, Medicaid or Medicare.
If another plan covered that date, bill it. Keep the CO-26 remittance as proof, and check the deadline with our timely filing calculator.
If the coverage was backdated, ask for reprocessing. This is common for newborns, Medicaid approvals and employer enrollment fixes. Call the payer once its eligibility file shows the right start date, and resubmit if it asks you to.
For a Medicare wellness visit in year one, do not appeal. The rule is working as written. Check whether the Welcome to Medicare visit was the right service instead.
If no coverage existed, bill the patient. Send a clear statement that explains the denial, and offer a payment plan or a financial assistance screening.

Medicaid Backdated Coverage and the 2027 Change

Federal Medicaid rules let coverage start up to three months before the month a person applied, as long as they were eligible in those months. That is why a Medicaid CO-26 can turn into a paid claim after the approval comes through. Some states already use a shorter window under a waiver.

This window is getting shorter for everyone. Under the 2025 budget law (H.R. 1, Section 71112), applications made on or after January 1, 2027 get less backdated coverage:

Group	Before 2027	Applications from January 1, 2027
Adults in the Medicaid expansion group	Up to 3 months	Up to 1 month
Children, people 65 and older, people with disabilities	Up to 3 months	Up to 2 months
CHIP	Varies by state	Up to 2 months

For practices, this means fewer uninsured visits will be rescued by a later Medicaid approval. Screen uninsured patients for Medicaid early, and help them apply in the same month as the visit when you can.

CO-26 vs Similar Denials

Code	What the payer is saying	What to do
CO-26	The visit was before the coverage started	Find the plan that covered that date
CO-27	The visit was after the coverage ended	Find the new plan, or bill the patient
CO-31	We cannot find this patient as a member	Fix the name, birth date or member ID
CO-109	You sent the claim to the wrong payer	Send it to the right plan or contractor
CO-22	Another plan should pay first	Update coordination of benefits

Appeal Wording When the Start Date Is Wrong

Appeal only if the patient really was covered on the date of service. Adapt this wording and attach the proof it mentions:

Claim [number] for date of service [date] was denied with reason code 26 (expenses incurred prior to coverage). The member's coverage was effective [start date], as shown on the attached [eligibility response, enrollment confirmation or employer letter]. Please correct the eligibility record and reprocess the claim.

How to Prevent CO-26

Check eligibility at every visit, and read the coverage start date, not just "active."
Ask new patients and anyone who changed jobs when their plan started.
For new Medicare patients, check the Part B start date before you schedule a wellness visit.
Flag newborn accounts and confirm the baby has been added before you send the claim.
Keep both the old and new insurance on file during plan changes, so you can bill the right one fast.

Sources: X12 Claim Adjustment Reason Code list and X12 interpretation RFI 976; CMS Change Request 7079 (Transmittal R2159CP, annual wellness visit edits); 42 CFR 435.915 (Medicaid effective dates); H.R. 1 (2025), Section 71112.

Frequently Asked Questions

What does denial code CO-26 mean?

CO-26 means the payer says the service happened before the patient's coverage with that plan started. The official text is "Expenses incurred prior to coverage." It is the opposite of CO-27, where the coverage had already ended.

Can I bill the patient for a CO-26 denial?

Only after you check for other coverage on the date of service. If an old plan, COBRA, a spouse's plan, Medicare or Medicaid covered that date, bill it. If no coverage existed, the patient is self-pay for that visit. Most payers send this code with group code PR, which points to patient responsibility.

What is the difference between CO-26 and CO-27?

CO-26 means the date of service was before the coverage started. CO-27 means the date of service was after the coverage ended. Both are fixed the same way: find the plan that covered the patient on that exact date.

Why did Medicare deny an annual wellness visit with reason code 26?

Medicare does not cover the annual wellness visit in the first 12 months of Part B. CMS told its contractors to deny these claims with reason code 26 and remark code N130. In the first year, the covered visit is the Welcome to Medicare preventive visit (G0402).

How far back can Medicaid coverage go?

Today, Medicaid can cover up to three months before the month the person applied, if they were eligible then. For applications made on or after January 1, 2027, federal law cuts this to one month for expansion adults and two months for most other enrollees.

Reviewed by Hassan Raza Awan, Founder — 4+ years of hands-on U.S. medical billing experience. General billing information — verify against current CMS guidance and your payer contracts.

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