A married couple is covered by their own separate employer group health plans, and their child is a dependent under both plans. Under the coordination of benefits 'birthday rule,' the child's primary plan is:

Why B is correct

Under the coordination of benefits (COB) birthday rule, when a dependent child is covered by both parents' group plans, the plan of the parent whose birthday occurs earlier in the calendar year is primary; the other parent's plan pays secondary benefits. The rule uses the month and day of birth, not the year, so the older parent is not automatically primary. This rule prevents overpayment and sets a predictable order of payment when two group plans cover the same dependent child.

Why the other options are wrong

• C) The birthday rule uses the earlier calendar-year birthday, not the parent's age; a younger parent with an earlier birthday can be primary. The birthday rule keys on the calendar order of the parents' birthdays, and age is not the operative factor in coordination of benefits determinations.
• D) The length of time a plan has been in force is not the COB test for dependent children under the birthday rule. Length of time the policy has been in force is used in some COB situations, but for dependent children of married parents the birthday rule governs instead.
• A) The earlier birthday, not the later one, determines the primary plan under the birthday rule. The plan of the parent whose birthday falls earlier in the year is primary, so the later birthday makes that parent's plan secondary rather than primary.

Memory hook

Birthday rule: the parent whose birthday hits first in the year carries the child's primary coverage.