Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
birth·day rule(bĭrth'dā rūl)
A principle involving coordination of benefits of health insurance plans to determine which insurance plan should cover costs of health care for dependent children; states that the insurance of the parent whose birth month is first in the calendar year is primary. (If both are in the same month, then coverage derives from the plan carried by the parent born earlier in the month. If both are the same month and day, coverage comes from the parent who has been covered for a longer period.)
Medical Dictionary for the Health Professions and Nursing © Farlex 2012