Income is one of the last factors that might be used to determine which parent can claim a dependent. These are the main requirements to claim a dependent that should be considered first. From IRS Publication 501:
Relationship - Dependent should be
Your son, daughter, stepchild, foster child, or a descendant (for example, your grandchild) of any of them, or
Your brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant (for example, your niece or nephew) of any of them.
Age - Is the child under 19, or between 19-24 and a full time college student?
Residency - Which parent lived with the child for more than half the year (or the majority of the year)?
The child cannot be claimed as a dependent if they provided more than half of their support.
For older children, the cannot be claimed as a dependent if they file a joint return.
If both parents lived with the child for the same amount of time, there are tie-breaker rules that are applied:
Tiebreaker rules. To determine which person can treat the child as a qualifying child to claim these six tax benefits, the following tiebreaker rules apply.
If only one of the persons is the child's parent, the child is treated as the qualifying child of the parent.
If the parents file a joint return together and can claim the child as a qualifying child, the child is treated as the qualifying child of the parents.
If the parents don't file a joint return together but both parents claim the child as a qualifying child, the IRS will treat the child as the qualifying child of the parent with whom the child lived for the longer period of time during the year. If the child lived with each parent for the same amount of time, the IRS will treat the child as the qualifying child of the parent who had the higher adjusted gross income (AGI) for the year.
If no parent can claim the child as a qualifying child, the child is treated as the qualifying child of the person who had the highest AGI for the year.
If a parent can claim the child as a qualifying child but no parent does so claim the child, the child is treated as the qualifying child of the person who had the highest AGI for the year, but only if that person's AGI is higher than the highest AGI of any of the child's parents who can claim the child. If the child's parents file a joint return with each other, this rule can be applied by dividing the parents' combined AGI equally between the parents. See Example 6.
Subject to these tiebreaker rules, you and the other person may be able to choose which of you claims the child as a qualifying child.
