<<how should he claim? He is claiming one and his ex is claiming their other child.>>
The right to claim a child belongs to the custodial parent, which the IRS defines as the parent with whom the child spent more than half the year. Since there are 365 days in the year, the split cannot be half and half.
The custodial parent may relinquish their right to claim a child to the non-custodial parent by providing them with a completed and signed Form 8332, which the non-custodial parent must then submit with their tax return. Here's a link to that form: https://www.irs.gov/pub/irs-pdf/f8332.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
