When a dependent is covered by both parents' health plans, what rule applies to determine which plan is primary?

The birthday rule is a widely accepted guideline used to determine which parent's health insurance plan is considered primary when both parents cover a dependent child. Under the birthday rule, the plan of the parent whose birthday falls earlier in the calendar year will be the primary insurer. This method is designed to provide a straightforward and fair way to determine insurance responsibility, avoiding potential disputes between parents regarding which plan should pay first.

This rule stems from the idea that the parent who has the earliest birthday has been insuring the child longer, thus their plan is prioritized. The secondary insurance will then cover any remaining eligible expenses not covered by the primary plan.

The older parent's plan, income level, or which parent's employer’s plan is chosen do not play roles in determining which plan is primary. Therefore, knowing and applying the birthday rule is essential for navigating situations where multiple health insurance plans are available for dependents.