For most of the last century, the majority of custody arrangements were quite simple: the mother got custody of the children and, as a result, the right to call them dependents. In recent years, however, custody agreements have become quite creative and custody may be shared over weekends, vacations or during the workweek. These arrangements are complicated by the fact that neither the most recent version of the tax code, nor IRS regulations define exactly what the definition of custody or a custodial parent is.

Generally, a person can claim the kids as dependents only if he or she is designated as the custodian by court order. When there is no such agreement or order, or when joint custody applies, the custodial parent is considered to be the parent who has physical custody of the child for most of the year.

When parents share custody 50-50, they sometimes switch who claims the kids from year to year in order to share the tax benefit. That works best if there is only one child involved. But if there is more than one kid, the best bet to avoid confusion may be to split the dependency of the kids between the two parents, which is allowed even if both kids spend the same amount of time with each parent.