If you meet the tie breaker requirements for claiming the child, but the other parent has already claimed the child, you would need to complete your return including your child as a dependent but you will need to paper file (print and mail the return to the IRS). The IRS will then make the determination. This help article explains in more detail: What Happens When Both Parents Claim a Child on a Tax Return?
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
