# Dental insurance birthday rule calculator > Determine which parent's dental plan is usually primary for a child covered by both parents' plans. URL: https://dentovio.com/tools/dental-insurance-birthday-rule Last verified: 2026-07-09 General coordination-of-benefits reference only; not legal advice or a coverage determination. Plan documents, court orders, state law, and carrier rules can change the result. ## Direct answer - The parent whose birthday falls earlier in the calendar year is usually primary for a dependent child. - Only the month and day matter; birth year does not matter. - A divorce decree or custody order can override the birthday rule. - If both parents have the same birthday, the plan that has covered the child longer is usually primary. ## Frequently asked questions ### What is the birthday rule for dental insurance? When a child is covered by both parents' dental plans, the birthday rule makes the plan of the parent whose birthday falls earlier in the calendar year the primary coverage. Only the month and day matter — not the birth year, so the older parent is not automatically primary. ### What if both parents have the same birthday? If both parents share the same month and day, the birthday rule can't break the tie. The plan that has covered the child longer is treated as primary. Confirm with both carriers. ### Does the birthday rule apply after a divorce? No. A divorce decree or custody order that assigns responsibility for the child's health coverage overrides the birthday rule. Without a court order, the custodial parent's plan is generally primary. ## Sources - `NAIC-MO-120` NAIC Coordination of Benefits Model Regulation. Common order-of-benefit rules, including birthday-rule and court-decree sequencing. ## Related - [Dental coordination of benefits calculator](https://dentovio.com/tools/dental-coordination-of-benefits-calculator/index.html.md) - [Free dental tools and calculators](https://dentovio.com/tools/index.html.md)