Which parent's insurance plan is considered primary if their birthdays fall on different days within the same year?

In determining which parent's insurance plan is considered primary when both parents have coverage and their birthdays fall on different days within the same year, the standard guideline states that the parent whose birthday falls earlier in the year holds the primary insurance responsibility. This method is known as the birthday rule and is commonly used to resolve conflicts between parents' health insurance plans.

The birthday rule operates under the premise that the parent who celebrates their birthday first in the calendar year is deemed the primary policyholder. This approach simplifies coordination of benefits between multiple insurance policies, ensuring that the primary coverage applies first to the healthcare expenses of the child.

In this context, the other options provided would not apply effectively. For instance, assessing the length of coverage or custody status does not align with the established birthday rule, which directly relates to the timing of the parents' birthdays.