Claims guide

Secondary Claims: How to Bill the Second Payer Correctly

Secondary claims are the claims you send to a patient's second insurance after the first insurance has processed the visit. Done right, secondary claims pick up part of the balance the primary plan left behind. This guide shows therapists, psychiatrists, and their billing staff how to sort out who pays first, what to attach, and how to follow up.

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What secondary claims are and when you need them

A secondary claim is the second bill for the same visit.

When a patient has two health plans, the plans take turns. The first plan, called the primary payer, processes the claim first. The second plan, called the secondary payer, may then pay part of what is left. Secondary claims are how you ask for that second payment. Without them, money sits unpaid or gets pushed to the patient by mistake.

The process of deciding which plan goes first is called coordination of benefits (COB). CMS describes COB as the rules that decide which plan pays first and how much each other plan adds, with the goal that total payments never go over 100% of the claim (CMS Coordination of Benefits, checked 10/10/26). Your secondary claims should follow that same idea: the second plan pays based on what the first plan did, not on the full charge alone.

Secondary claims matter for both psychotherapists and psychiatrists. A therapist usually sends a psychotherapy code. A psychiatrist often sends an evaluation and management (E/M) code, sometimes with an add-on psychotherapy code. Either way, the second payer wants to see what the first payer allowed, paid, and adjusted. Secondary claims fail when that picture is missing.

MCM South works secondary claims every week for psychotherapists and psychiatrists. For the basics of claim wording, see our claims processing glossary.

Who pays first: private, Medicare, and Medicaid rules

The order for secondary claims depends on the type of coverage. Keep the three types separate.

Private plans and the Birthday Rule

For a child covered by two parents' plans, many plans use the Birthday Rule. Under the National Association of Insurance Commissioners (NAIC) model language, when the parents are married or live together, the plan of the parent whose birthday falls earlier in the calendar year is primary. If the birthdays match, the plan that has covered the parent longer goes first (New Mexico Office of Superintendent of Insurance Bulletin 2025-015, checked 10/10/26).

That bulletin also covers separated and divorced parents. A court decree that assigns health care responsibility to one parent controls. If there is no decree, the order runs from the custodial parent's plan to that parent's spouse's plan, then the non-custodial parent's plan, then that parent's spouse's plan. This is one state's notice of the model language. Rules vary by state and by plan, so confirm with the payer.

For adults with two employer plans, do not assume. Ask each payer which one is primary. Your private insurance guides list how to reach the major plans.

Medicare as secondary payer

Medicare is not always first. The Medicare Secondary Payer (MSP) program exists so that Medicare does not pay first when another insurer should. CMS says COB rules decide the order when a person has Medicare plus other coverage, including group health plans and non-group plans such as liability, no-fault, and workers' compensation (CMS Coordination of Benefits & Recovery overview, checked 10/10/26).

The Benefits Coordination & Recovery Center (BCRC) researches MSP cases, not your local Medicare office. CMS also relies on providers to ask Medicare patients about other primary coverage and to report it on claims (CMS provider services page, checked 10/10/26). If another insurer is primary, Medicare may deny a claim and tell you to bill the right party.

Medicaid and state rules

Medicaid has its own rules, and they differ by state. Do not copy a Massachusetts workflow into Texas, or the reverse. Use the state Medicaid agency's billing manual for the state you bill. CMS notes that Medicaid agencies are among the groups that can receive Medicare-paid claim data through the COB Agreement program, but your state's manual controls how and when you bill.

Crossover or direct submission: which one applies

Some secondary claims move on their own. Many do not.

Crossover means the primary payer's claim data is passed to the second payer without you sending a new claim. For Medicare, CMS says the BCRC sends Medicare-paid claim data to supplemental insurers so they can pay as secondary. That automatic crossover happens only when the BCRC has an agreement with the insurer. Without one, the patient or the practice has to coordinate the second payment (CMS Coordination of Benefits).

Look at the primary remittance for a crossover note. If you see none, call the second payer and ask whether it received the claim. If not, send it yourself.

Crossover versus direct submission for secondary claims
Situation	What usually happens	What you do
Medicare primary, supplemental plan has a COB agreement	Claim data may cross over automatically	Check the remittance for a crossover note, then wait for the second payer
Medicare primary, no agreement in place	No automatic transfer	Send the secondary claim yourself with the Medicare remittance
Private plan primary, private plan secondary	Usually no automatic transfer	Send a secondary claim with the primary explanation of benefits (EOB) or electronic remittance
Medicaid secondary to another plan	Varies by state	Follow your state Medicaid billing manual

Five steps to send secondary claims

Use the same routine for secondary claims on every visit that has two plans.

Confirm both plans at intake. Collect both cards and ask who is the subscriber on each. Run an eligibility check on both plans before the first visit.
Decide the order. Use the Birthday Rule or plan rules for private coverage, and the MSP rules for Medicare. When two plans disagree about who is first, ask both for their COB record and wait for the answer in writing.
Bill the primary payer first, and wait for the remittance. Read the allowed amount, paid amount, patient responsibility, and adjustment reasons. Our electronic remittance advice guide shows how to read each part.
Build the secondary claim. Report the primary payer's information on the claim and attach or send the primary payment data. Report what the first plan paid.
Send, track, and post. Submit within the second payer's filing window, check status, and post the payment. Move any balance the second plan does not cover to patient responsibility only if your contract allows it.

Two cautions. First, do not bill the secondary payer before the primary has processed the claim, unless the second payer tells you otherwise. Second, if the primary payer denied the claim for a fixable reason, fix it first. A bad primary claim makes bad secondary claims. Our guide to claim denials and appeals covers the fix-and-resubmit path.

Where secondary claims show up on the CMS-1500

The paper form tells the second payer that other coverage exists.

The National Uniform Claim Committee (NUCC) publishes the instruction manual for the CMS-1500 form. The table below paraphrases the July 2025 manual for the boxes that matter most on secondary claims (NUCC 1500 instruction manual, checked 10/10/26). Electronic claims carry the same facts, and your billing software maps them.

CMS-1500 boxes used when another plan is involved
Box	Name	What the manual says
11d	Is there another health benefit plan?	Mark yes or no. If yes, complete boxes 9, 9a, and 9d.
9	Other insured's name	Complete only when 11d is marked yes. Enter the other plan's enrollee name if it differs from box 2.
9a	Other insured's policy or group number	Enter the number with no hyphens or spaces.
9d	Insurance plan or program name	Enter the other plan's name.
11c	Insurance plan or program name	Enter the insured's plan name. Some payers want the primary insurer's ID number here instead.
10a-10c	Condition related to	A yes for employment, auto, or other accident can mean another coverage is primary, and that coverage is then shown in box 11.
22	Resubmission code	Code 7 replaces a prior claim and code 8 voids one. Use it only for resubmitted claims, not originals.

The manual does not describe the Birthday Rule or any order-of-benefits test. It directs users to payer, clearinghouse, or vendor instructions for those rules. See our full CMS-1500 guide for the rest of the form.

How do I bill secondary claims after the primary pays?

This is the question we hear most from new billing staff.

Short answer: Wait for the primary payer's remittance. Then send the second payer a claim that shows the other coverage and the primary payment, either through crossover or direct submission. Post the second payment against the balance the first payer left, and bill the patient only for what both plans leave as patient responsibility.

Common reasons secondary claims get denied

The second payer says the order is wrong, so you bill the other plan first.
The primary remittance was missing or unreadable.
The claim reached the second payer after its filing window closed. Ask each payer for its window; do not assume.
The member ID or plan name in the other-insurance fields does not match the card.
The claim shows the full charge but no primary payment.

Look up denial wording in our claim denial terms glossary. If the problem is the order of benefits, call both payers and ask them to update their COB record. That one call can fix every future visit.

What to do Monday morning

Start small and fix the front end first.

Pull a list of patients with two plans and check that both are verified, so secondary claims have what they need.
Check every open claim with a primary payment and no secondary claim sent.
Call one payer you bill often and write down its secondary claim filing window and crossover practice.
Add the other-insurance fields to your intake form if they are missing.
Review the practices we serve page if you want a second set of eyes on a stalled balance.

Frequently asked questions

What is a secondary claim?

Secondary claims are the bills you send to a patient's second insurance after the first insurance has processed the visit. They show what the primary plan paid so the second plan can consider the remaining balance.

What is the Birthday Rule?

For a child covered by both parents' plans, the plan of the parent whose birthday falls earlier in the calendar year is usually primary. If the parents are separated, a court decree or custody rules can change the order. Check each plan's wording.

Does Medicare always pay first?

No. Under Medicare Secondary Payer rules, Medicare can be second when other coverage, such as a group health plan or liability coverage, should pay first. The Benefits Coordination and Recovery Center researches these cases.

Do secondary claims cross over on their own?

Sometimes. Medicare data for secondary claims crosses over automatically only when the insurer has an agreement with the Benefits Coordination and Recovery Center. Otherwise you send the claim yourself.

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