Primary and Secondary Insurance Claims: How to Bill
By George Ruan • October 7, 2026
Last reviewed: October 7, 2026.
Bill the primary plan first and wait for its EOB or ERA. Then send the secondary claim with the primary’s payment, adjustments, and claim number. Before any of that, confirm the order with the payers themselves, because cards and clients often have it backwards. Also check whether the primary already passed the claim to the secondary through a crossover.
Sections
Confirm which plan is primary
The usual rules: a plan that covers the client as the employee or subscriber pays before a plan that covers them as a dependent. With Medicare and an employer plan, the order depends on whether the client (or spouse) is still working and on the employer’s size. With a Medigap or Medicare supplement, Medicare is primary. CMS requires providers billing Medicare to find out whether another payer should pay first.
In practice, the payer’s coordination-of-benefits (COB) record controls, even when it is wrong. In one case a commercial plan’s eligibility response listed Medicare as primary for a client who had never had Medicare. A family member with the same name did. The plan was treating itself as secondary. Only the member could correct it, by calling the plan’s member services, so we held the claims until the plan confirmed the fix.
The primary-to-secondary handoff
Submit to the confirmed primary and keep its acknowledgment and claim number.
Wait for the primary’s EOB or ERA. A secondary claim generally cannot go out until the primary has finalized.
Check the primary remittance for a crossover note before filing anything to the secondary.
Build the secondary claim from the remittance: primary paid amount, patient responsibility, adjustment codes, and the primary’s payer claim number.
Track the secondary claim’s acknowledgment and adjudication on its own, with both claim numbers recorded together.
SimplePractice’s secondary-claim guide also requires the primary remittance details before filing, either imported from its payment reports or entered from the EOB or ERA. Review what was imported rather than assuming every adjustment carried over. SimplePractice: filing secondary claims.
When the secondary gets the claim automatically
Medicare supplements (Medigap). These claims typically cross over from Medicare automatically, so you usually do not file a separate secondary claim. CMS describes these crossover agreements. CMS: coordination of benefits.
Medicaid as secondary. Crossover may or may not happen depending on the product. Check the Medicare remittance for a crossover indicator and confirm with the Medicaid program before filing directly. Medicare Advantage claims do not automatically cross over to some state Medicaid programs.
Commercial plans. Aetna, for example, says certain Medicare remittance remarks mean the claim was already forwarded to it. Follow the receiving plan’s instructions instead of sending a duplicate. Aetna: claim coordination.
What tends to go wrong
A wrong COB record at the payer. Claims deny or pay as secondary until the member gets the plan to correct it.
The secondary waits on a slow primary. A secondary claim follows only after the primary pays, so a pending primary holds both.
A secondary claim missing the primary’s claim number. Some systems will not send it until the primary EOB is posted and that number is attached.
A paper EOB arrives before the electronic remittance. Post from whichever authoritative copy arrives first, and do not post it twice when the second one shows up.
A supplement that was suspended or ended. If a client’s secondary coverage is in question, hold automatic client charges until it is clarified.
Medicare not enrolled. If Medicare is primary and the clinician is not enrolled, there is no Medicare adjudication for the secondary to work from. See Medicare participating vs. not enrolled.
Settle the client balance last
Reconcile both remittances before you bill the client. The secondary plan applies its own benefits and coordination method; Aetna’s provider manual describes several, including cases where no extra benefit is paid. Aetna office manual. When Medicaid is secondary, what Medicaid does not pay is usually a contractual write-off, not a client balance. For clients with Qualified Medicare Beneficiary (QMB) status, Medicare cost sharing cannot be billed to the client at all.
If a claim keeps landing at the wrong plan, see the payer ID and claim-routing checklist.
Related Guides
Frequently Asked Questions
The client says their new plan is primary. Can I bill it first?
Check the payers’ own COB records first. Clients often state the order backwards, and the plan will process the claim according to its record, not the client’s belief.
Can I send the secondary claim after the primary denies it?
Often yes. A primary denial is still an adjudication the secondary can use, but check the denial reason and the secondary plan’s rules. It does not mean the secondary owes the balance.
Will the secondary pay the whole copay or deductible?
Not necessarily. It applies its own benefits and coordination rules, so wait for its adjudication before you set the client’s balance.
Sources
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Founded by George Ruan, Dax Earl, and Andrey Goder, Bomi helps independent therapists and group practices with insurance billing, credentialing, and payer follow-up. Bomi grew out of Dax’s experience helping his mother with her therapy practice, with a clear purpose: reduce the administrative burden of insurance while keeping practice owners in control.
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