Birthday Rule Coordination of Benefits for Therapy Claims
Birthday rule coordination of benefits is how insurers decide which parent’s plan pays first when a child is covered under both parents’ health plans. A wrong guess means a rejected claim and slower payment, so this guide shows how to apply it before you bill, with a link to our walkthrough of secondary claims for therapists.
Birthday rule coordination of benefits: what it says
The Birthday Rule says that when a child is covered by both parents’ plans, the plan of the parent whose birthday comes earlier in the calendar year pays first. Only the month and day count, never the birth year. If both parents share a birthday, the plan that has covered a parent longer is primary. This is the approach in the National Association of Insurance Commissioners (NAIC) Coordination of Benefits Model Regulation (October 2013 compilation, checked 10/23/26).
The rule is one piece of Coordination of Benefits (COB), the rules that keep two plans from paying the same bill twice. The primary plan pays as if no other coverage existed, and the secondary plan looks at what remains.
Who pays first: a quick reference
The table follows the NAIC model text (checked 10/23/26). Plans and states can word their rules differently.
| Situation | Primary plan under the NAIC model |
|---|---|
| Adult covered as an employee on one plan and a dependent on another | The plan covering the person as an employee |
| Child, parents married or living together | The parent with the earlier birthday (month and day) |
| Child, divorced parents, decree assigns health coverage to one parent | That parent’s plan, once it knows of the decree |
| Child, joint custody decree with no assignment | Birthday rule |
| Child, divorced or apart, no decree | Custodial parent’s plan, then that parent’s spouse’s, then the other parent’s, then that parent’s spouse’s |
How do I know which parent’s plan is primary for a child?
Collect both plans’ information and each policyholder’s birth month and day at intake, then confirm the order with the payers before you bill. A court order or a plan’s own records can change the answer. Here is a five-step check for Monday morning:
- Ask at intake whether the child has more than one plan.
- Get each plan’s member ID, policyholder name, and the policyholder’s birth month and day.
- Ask whether a divorce or custody order says who must provide health coverage.
- Check eligibility with both payers and ask which plan each one lists as primary.
- Record the order in your billing system and recheck it each plan year.
Divorced parents and state differences
Birthday rule coordination of benefits follows a model rule, not a single national law. States adopt their own versions, so wording and exceptions differ. Never assume a neighboring state works the same way.
Private plans and court orders
Under the NAIC model, a court decree that assigns health coverage responsibility to one parent overrides the birthday rule, as long as that parent’s plan has actual knowledge of the decree. Without a decree, the custodial parent’s plan comes first.
State rules
Connecticut’s Office of the Healthcare Advocate explains the birthday rule and says a court order on health coverage can override it (checked 10/23/26). The Illinois Administrative Code, Title 50, Section 2009.40 sets out the same basic order in its own wording, including a provision for plans that still use a gender-based rule. The NAIC text we reviewed does not mention that provision (checked 10/23/26).
Medicare is different
Medicare does not use the birthday rule. It follows Medicare Secondary Payer (MSP) rules, which tell you when another payer must go before Medicare.
Medicare Secondary Payer basics
Per the Centers for Medicare & Medicaid Services (CMS) MSP page (modified 9/10/24, checked 10/23/26), an employer group health plan pays first for a client age 65 or older when the employer (or the spouse’s employer) has 20 or more employees. Medicare pays first when the employer has fewer than 20. For a client on Medicare because of disability, the employer plan pays first when the employer has 100 or more employees. CMS also relies on providers to ask Medicare patients about other coverage (modified 6/10/26, checked 10/23/26). See our Medicare behavioral health billing guide for the rest of the Medicare picture.
Filing the secondary claim
Once the primary payer finishes under birthday rule coordination of benefits, you bill the second plan for what is left. The primary payer’s Explanation of Benefits (EOB) or electronic remittance shows what it paid and adjusted, and the second plan needs that detail. Our secondary claims resource walks through the claim itself.
If you billed the wrong plan first, fix it before the claim ages. A Clean Claim to the right payer in the right order is the goal, and a corrected claim may be needed if the first submission went out wrong. For payer contact paths, see our insurance companies contact directory.
How MCM South helps
MCM South Medical Billing Service exclusively serves mental and behavioral health practices, including psychotherapists and psychiatrists. We verify which plan is primary, bill in the right order, and follow up on secondary claims billing so the second payer is not forgotten.
Birthday rule coordination of benefits: the short version
In short, birthday rule coordination of benefits picks the parent whose birthday falls earlier in the calendar year, unless a court order says otherwise. Add a line about birthday rule coordination of benefits to your intake checklist so no claim goes to the wrong plan first.
Frequently asked questions
Does the birthday rule use the year a parent was born?
No. Only the month and day count, so the parent whose birthday falls earlier in the calendar year has the primary plan. If both share a birthday, the plan that has covered a parent longer is primary, per the NAIC model.
What if the child’s parents are divorced?
A court decree that assigns health coverage to one parent generally controls, once that parent’s plan knows about it. Without a decree, the NAIC model puts the custodial parent’s plan first. Rules vary by state and plan, so confirm with the payers.
Does Medicare use the birthday rule?
No. Medicare follows Medicare Secondary Payer rules, which depend on factors such as employer size. See our [[/resources/medicare-behavioral-health-billing/|Medicare behavioral health billing guide]].
How do I bill the second plan once the first one pays?
Send the secondary claim with the primary payer’s payment and adjustment details. Our [[/secondary-claims-for-therapists/|secondary claims for therapists]] post walks through the steps.
Where MCM South works
MCM South works only in mental and behavioral health. We serve psychotherapists and psychiatrists in solo and medium-size practices across ten currently served states: Georgia, Massachusetts, Connecticut, Texas, Florida, New York, Colorado, Tennessee, North Carolina and Illinois. Need a payer contact? Use our insurance companies contact directory.
