So you and your spouse both want to claim your child as a dependent on your taxes, but you know that you're not allowed to claim him or her twice in California, seeing as how you're divorced. Typically, the parent who has custody is able to make the claim, while the other is not, but there are situations in which both parents have custody. The following rules may be used to break the tie.
-- If just one of you is biologically related to the child, then only the biological parent counts.
-- If the child lived with one parent for more than 50 percent of the year, that parent can make the claim.
-- If the parents each had the child for exactly 50 percent of the time, the Internal Revenue Service then looks at the adjusted gross income of each parent and allows the parent with the higher income to make the claim.
The court is simply trying to figure out who really spent the most time and money supporting the child. If a mother has the child five days a week, for example, and the father just sees the child for a day and a half on the weekends, the court knows that the mother had to cover more costs -- everything from food to the electric bill -- than the father. The court also knows that the mother had to put more time into caring for the child, while the father had more time to work, and therefore, the mother needs the tax exemption in this hypothetical example. This is not to say that mothers always get the exemption.
Be sure you know exactly how your custody agreement is going to impact your tax filings and other expenses.
Source: IRS, "Publication 504 - Main Content," accessed June 02, 2016