How to Submit Secondary Insurance Claims: Checklist

To submit a secondary insurance claim, bill the primary plan first, wait for its remittance (the EOB or ERA), then send the secondary plan a claim that reports what the primary paid, adjusted and assigned to the patient on each line. Do not send it yourself if the primary payer has already forwarded it: on a Medicare remittance, remark code MA18 means the claim was also forwarded to the patient's supplemental insurer, and sending it again creates a duplicate.

The checklist:

1. Collect every active plan and confirm which is primary using coordination-of-benefits rules.
2. Wait for the primary payer's decision (paid, applied to deductible or denied) and read the remittance.
3. Check whether the claim crossed over automatically (MA18 on a Medicare remittance).
4. Build the secondary claim with the primary payer's paid amount, adjustment group and reason codes, and patient responsibility for each line.
5. Submit electronically where the secondary payer accepts electronic coordination-of-benefits data, within its filing limit.
6. Track and answer requests until the secondary claim is paid or denied.

Sources checked October 14, 2026 · Prepared by Prospyr. No certified-coder or clinician review is claimed. CPT is a registered trademark of the American Medical Association; use the current licensed code set.

Step 1: Verify every plan and the coverage order

Collect complete insurance information

Ask for every active insurance card at each visit and scan the front and back. Patients often forget a spouse's plan, retiree coverage or a Medicare supplement. Ask directly: "Are you or your spouse working?" and "Have you enrolled in Medicare?" Retirement, marriage, divorce, a new job and turning 65 all change which plan pays first.

Confirm eligibility electronically (the 270/271 transaction) through your clearinghouse or a payer portal. When you call a payer, note the representative's name, the reference number and the date.

Apply coordination-of-benefits rules

Most state rules for commercial plans follow the NAIC Coordination of Benefits Model Regulation. Medicare's own rules decide when Medicare is primary.

Edge cases (end-stage renal disease, multi-employer plans, workers' compensation, liability claims) have their own rules. Check the CMS Medicare Secondary Payer guidance or the plans themselves.

Step 2: Get and review the primary payer's remittance

Submit the secondary claim only after the primary claim is finalized. Sending it before the primary payer decides is a common reason for rejection.

Review the EOB or ERA:

• the date the primary payer processed the claim,
• the allowed amount, the amount paid and each adjustment, line by line,
• the adjustment group code and claim adjustment reason code (CARC) on each adjustment.

If the remittance shows an error, such as a wrong modifier, NPI or unit count, fix it with the primary payer first.

Record the primary payer's claim number (sometimes called the payer claim control number or ICN). Secondary payers often need it to match the two claims.

Step 3: Prepare and submit the secondary claim

• Report the primary adjudication. On an electronic 837P, the primary payer's payment and adjustments go in the other-payer (coordination-of-benefits) loops. If your system can load these from the 835 remittance, use that instead of re-keying.
• Make every line balance. The primary payer's paid amount plus its adjustments should equal the billed charge for each line. A line that does not balance is a common reason for a secondary rejection.
• Use the right form for paper claims. Professional services go on the CMS-1500; institutional services on the UB-04 (CMS-1450). Use the official red-ink forms so payers' scanners can read them, and attach the primary EOB if the secondary payer requires it.
• Protect other patients' information. If a paper EOB lists other patients, black out their details before you send it.
• Check for crossover first. If the primary remittance shows MA18 or the payer confirms it forwarded the claim, do not submit a second copy.
• Watch the secondary plan's filing limit. Some plans count from the date of service and some from the primary payer's processing date. Check the plan's rules and your contract; limits vary by plan and contract. When Medicare is the secondary payer, its one-calendar-year limit from the date of service still applies.

Step 4: Track and follow up

• Filter your claim list for secondary claims so they do not sit unnoticed behind primary work.
• Enroll in electronic remittance advice so you see the final decision, not only "accepted."
• Set follow-up rules, such as contacting the payer when a claim has been accepted but not processed after a set number of days, and answer requests for information promptly.
• If the rejection says secondary claim information is missing or invalid, recheck that each line balances and that the primary payer's claim number is included.

Where Prospyr fits

Prospyr supports charting, digital intake (including insurance card capture), inventory and practice operations. It does not create, submit or track primary or secondary insurance claims. Practices that bill insurance heavily need a separate claims solution.

Sources

• Medicare.gov: which insurance pays first
• CMS: Medicare Secondary Payer
• NAIC Coordination of Benefits Model Regulation (Model 120)
• X12: claim adjustment reason codes and group codes
• BCBS Michigan provider bulletin: Medicare crossover claims identified by MA18
• 42 CFR 424.44: Medicare time limits for filing claims (Cornell LII)
• MACPAC: how Medicaid interacts with other payers