# Dental insurance birthday rule

> Which parent's dental plan is primary for a child covered by both parents? The rule, its tie-break, and the exceptions that override it.

URL: https://dentovio.com/dental-insurance-birthday-rule

Last verified: 2026-08-30

Dentovio is an independent publisher, not an insurance carrier, benefits administrator, the ADA, or any government agency. This page was drafted with AI assistance and verified against the primary sources linked here. It has not been reviewed by a credentialed dental billing specialist or attorney. These pages describe how the two most common coordination-of-benefits methods and the birthday rule work in general terms; the plan documents and each state's adopted COB rules control the actual order and amounts, and a self-funded employer plan is generally governed by ERISA rather than those state rules. Educational reference only — not legal, benefits, or billing advice; confirm the order of benefits and the secondary plan's coordination method with each carrier before quoting a patient.

## Direct answer

Under the birthday rule, when a dependent child is covered by both parents' dental plans, the plan of the parent whose birthday — month and day, not year — falls earlier in the calendar year pays first. If both parents share the same month and day, the plan that has covered the parent longest is primary. A court decree assigning responsibility for the child's health coverage overrides the birthday rule, and self-funded employer (ERISA) plans can follow a different order-of-benefits rule set by the plan document. The rule comes from the NAIC Coordination of Benefits Model Regulation as adopted into state law; the adopted state text and the plan documents control the actual order.

## The rule and its exceptions

- Earlier birthday in the calendar year — month and day only, the year is ignored — makes that parent's plan primary for the child.
- Same-day tie: the plan that has covered the parent longest is primary.
- 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 (ERISA) plans can set a different order in the plan document (29 U.S.C. § 1144).

## Examples

- March 14 comes before September 2 in the calendar year, so Parent A's plan is primary.
- Within the same month, the earlier day wins: June 6 beats June 21.
- Identical month and day — the plan that has covered the parent longest is primary.

## After primary is decided

The order only settles who pays first. How much the secondary then pays depends on its coordination method — see [dental coordination of benefits](https://dentovio.com/dental-coordination-of-benefits/index.html.md) for traditional vs non-duplication math.

## Sources

- [NAIC Coordination of Benefits Model Regulation (MDL-120)](https://content.naic.org/sites/default/files/model-law-120.pdf) — 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](https://content.naic.org/model-laws) — 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](https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title29-section1144&num=0&edition=prelim) — 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](https://www.ada.org/resources/practice/dental-insurance/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.

Research confidence: medium. The rule is quoted from the NAIC model-regulation text. Confidence stays medium because state adoption of the model was not verified against current state code — the adopted state text and the plan documents control the actual order.

## Related

- [Dental coordination of benefits](https://dentovio.com/dental-coordination-of-benefits/index.html.md)
- [Dental billing hub](https://dentovio.com/dental-billing/index.html.md)
- [Dental claim denial codes](https://dentovio.com/dental-claim-denial-codes/index.html.md)
- [Payer documentation requirements](https://dentovio.com/dental-claim-documentation/index.html.md)
- [Dental prompt-pay laws by state](https://dentovio.com/dental-prompt-pay-laws/index.html.md)