Sometimes a child meets the rules to be a qualifying child of more than one person. The following rules must be applied to determine who can claim the child as a qualifying child. Under the tie-breaker rule, the child is treated as a qualifying child:

• The parent, if only one of the persons is the child's parent,
• The parent with whom the child lived the longest during the tax year, if two of the persons are the child's parent and they do not file a joint return together,
• The parent with the highest AGI if the child lived with each parent for the same amount of time during the tax year, and they do not file a joint return together,
• A non-parent, if no parent claims the child as a qualifying child although he or she may do so and only if the non-parent's AGI is higher than the highest AGI of any parent who may claim the child, or
• The person with the highest AGI, if none of the persons is the child's parent.

This information is found in Publication 501, Dependents, Standard Deduction, and Filing Information.