The birthday rule is a common claims practice health insurance companies use when children are listed as dependents on two parents' group health plans. The rule helps determine which health plan is the primary policy and which is secondary so that total coverage does not exceed 100 percent of charges.
According to the birthday rule, the primary plan belongs to the parent whose birthday falls closest to the beginning of the year. The ages of the parents are irrelevant when determining the birthday rule. The primary plan pays out a benefit first and the secondary plan pays the remainder of the medical cost if it is a covered benefit on the secondary plan.
It’s important to remember that the "birthday rule" is not a law -- it is simply a practice that many insurers follow. Other insurance companies do not use the birthday rule.
Here is how the birthday rule typically is modified in some other situations:
It's important that you read your health insurance policies carefully and work with your insurance companies to understand how benefits are coordinated. Not all plans follow the birthday rule, so it's a good idea to determine which plan is the primary and which is the secondary before you start incurring medical costs.