In what scenario does the birthday rule apply?

The birthday rule applies specifically to scenarios involving the determination of primary coverage for a child who is covered by two parents' health insurance plans. According to this rule, when a child is covered by multiple plans, the plan of the parent whose birthday falls first in the calendar year is considered the primary insurance. This serves to streamline the process of determining which insurance company pays for healthcare expenses first and ultimately avoids confusion regarding coverage.

The other scenarios mentioned do not pertain to the birthday rule. Retirement age considerations or initiating a new healthcare plan do not involve the coordination of benefits between parents' plans for their child. Similarly, evaluating chronic illness coverage is unrelated to how primary and secondary insurance determinations are made in the context of dual coverage for minors.