Billing & claims · Last verified 2026-08-30
Dental insurance birthday rule
For a child on both parents' plans, the parent whose birthday falls earlier in the calendar year usually holds the primary plan. Check a specific case below.
Check which parent's plan is primary
Month and day only — the birth year never matters under the rule, so it is not asked for.
Primary plan for the child
Parent A's plan is primary
Parent A's birthday falls earlier in the calendar year, so Parent A's plan pays first for the child. The birth year — and which parent is older — is irrelevant.
A court decree assigning responsibility for the child's coverage overrides this result, and a self-funded (ERISA) plan can set its own order. Confirm with both carriers before billing.
How this check works
The earlier month-and-day in the calendar year wins: month × 100 + day, smaller value is primary. A same-day tie falls back to the plan that has covered the parent longer — this check cannot see effective dates, so it reports the tie instead of guessing. The rule comes from the NAIC Coordination of Benefits Model Regulation framework as adopted into state law, linked in the sources on this page (last verified 2026-08-30); the adopted state text and plan documents control the actual order.
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The rule
The parent with the earlier birthday in the calendar year is primary.
Year ignored
Month and day only — the older parent is not automatically primary.
Same-day tie
The plan that has covered the parent longest pays first.
Court decree
A decree assigning coverage responsibility overrides the rule.
When the birthday rule does not decide
- A court decree assigning responsibility for the child's health coverage overrides the birthday rule entirely.
- Divorced or separated without a decree: the NAIC model's order generally starts with the custodial parent's plan — the state's adopted text and the plan documents control, so confirm with both carriers.
- Self-funded employer plans are generally governed by ERISA rather than state insurance regulation (29 U.S.C. § 1144) — such a plan can set a different order in the plan document. A self-funded governmental or church plan is not an ERISA plan, so state law can reach it.
- States adopt different editions of the NAIC model with different amendments. Which state adopted which edition was not verified against current state code, so this page states the model framework, not any state's exact text.
After primary is decided
The order only settles who pays first. How much the secondary then pays depends on its coordination method — run the numbers on the coordination-of-benefits page, which models traditional COB and non-duplication with worked examples.
Common questions
- Does the parents' age matter under the birthday rule?
- No. Only the month and day of each birthday matter — the birth year is ignored, so the older parent's plan is not automatically primary.
- Does the birthday rule apply after a divorce?
- A court decree that assigns responsibility for the child's health coverage overrides the birthday rule. Without one, the NAIC model's order generally starts with the custodial parent's plan — but the state's adopted text and the plan documents control, so confirm the order with both carriers.
- Do the parents have to be married for the birthday rule to apply?
- No, but they do have to be married or living together — the NAIC model scopes the birthday rule to a dependent child whose parents are married or are living together, whether or not they have ever been married. Where the parents are not living together and no court decree allocates responsibility for the child's health coverage, the model runs a different order instead: the custodial parent's plan, then that parent's spouse's plan, then the non-custodial parent's, then that parent's spouse's. Confirm against the state's adopted text and both plan documents.
- There is a court decree — does it always beat the birthday rule?
- Not on its own. Under the NAIC model the decree controls only where it actually makes one parent responsible for the child's health care expenses or coverage, and only once that parent's plan has actual knowledge of the terms — the model expressly exempts any plan year in which benefits were paid before the plan knew of the decree. A decree that makes both parents responsible, or that grants joint custody without saying who carries health coverage, sends the order back to the birthday rule. Get the decree language on file with the carrier, not just in the chart.
- One parent is the subscriber on their own plan — does that make it primary?
- Not for the child. The subscriber rule decides order only for the same person: the plan that covers someone as an employee, member, subscriber, policyholder, or retiree pays before a plan that covers that same person as a dependent. A child is a dependent on both parents' plans, so that rule cannot settle it and the birthday, decree, and custody order applies instead.
Sources
- NAIC Coordination of Benefits Model Regulation (MDL-120) — Model order-of-benefit-determination rules most states adopt, including the birthday rule, the longer-coverage tie-break, and court-decree sequencing.
- NAIC model laws index — Where NAIC publishes current model text and state-adoption information. This cluster states no per-state COB rule, so no adoption row is published here.
- 29 U.S.C. § 1144 — ERISA preemption of state law — Why a self-funded employer plan is generally governed by ERISA rather than a state's COB rules, and can follow its own coordination method and order of benefits. The section never uses the words self-funded; the rule comes from the courts reading its preemption, saving, and deemer clauses together.
- ADA guidance on coordination of benefits — Practice-facing definitions of traditional COB, non-duplication, and the maintenance-of-benefits variants this calculator declines to model.
The full claim cycle, in order
Verification, documentation requirements, denial codes, and prompt-pay deadlines sit alongside this reference on one free hub, organized the way a claim moves.
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