TurboTax will ask “how long did the child live with you?“ Answer the entire year, which is the correct answer for a newborn no matter when in the year they were born. Then TurboTax will ask if you have a custody agreement with the other parent. Answer NO. This question only applies to legal custody agreements between parents who live apart due to separation or divorce. When your partner prepares their tax return, they should not indicate that they support someone and they should leave the child completely OFF their tax return.
The reason for this is that the TurboTax interview regarding custody is designed for parents who are divorced or separated and live apart and share custody under a court order, and can sometimes be misunderstood in the case of parents who are not married but who live together. In your situation, the easiest way to get the correct result is for the parent who wants to claim the child to claim the child and answer no to the custody question, and for the other parent to leave the child completely off their tax return.
