Which rule determines a child's primary coverage based on the earlier date of birth of the parents?

The birthday rule is a widely recognized guideline used in healthcare coverage to determine which parent's insurance plan is considered the primary coverage for a child. According to this rule, if both parents have health insurance plans that cover the child, the plan of the parent whose birthday comes first in the calendar year will be the primary coverage. This means that the month and day of birth are relevant, regardless of the year.

This rule helps streamline the process of determining who is responsible for paying for the child's health expenses first, thus minimizing disputes and potential confusion in situations where both parents are insured. It provides a straightforward method of establishing primary and secondary coverage based on an easily identifiable criterion: the birthdays of the parents, rather than relying on more complex factors such as custody agreements or the gender of the parents.

In contrast, other rules mentioned in the options, like the gender rule, custody rule, and parent rule, do not have standardized applications in determining insurance coverage for children in the same widely accepted manner as the birthday rule does.