Can you explain the birthday rule with health insurance?

The birthday rule is a method used by health insurance companies to determine which insurance plan is the primary insurer for dependents covered under multiple plans. The rule is based on the birth month and day of the policyholders, typically the parents. Under the birthday rule, the primary health insurance plan for a dependent is the one held by the parent whose birthday comes first in the calendar year. For example, if the father's birthday is in January and the mother's birthday is in March, then the father's health insurance plan would be considered the primary insurance for the dependent, and the mother's health insurance plan would be considered the secondary insurance. The birthday rule applies only to dependents who are covered under more than one health insurance plan. It is used to avoid duplication of benefits, which can occur when two insurance plans cover the same medical expenses. In such cases, the primary insurance plan is responsible for paying the majority of the medical expenses, while the secondary insurance plan covers the remaining costs. The birthday rule is widely used in the United States and is recognized by most health insurance companies. However, some insurance companies may use different methods for determining which plan is the primary insurance, so it is important for policyholders to review their plan documents carefully to understand how their insurance works.