Under the 'birthday rule' for coordinating benefits on a dependent child covered by both parents' plans, the primary plan is generally the one belonging to the parent whose:

解析

The birthday rule states that when a child is covered under both parents' plans, the plan of the parent whose birthday (month and day) comes first in the calendar year is primary. The year of birth is not considered. This common COB rule helps payers consistently decide the order of payment.