If both parents live together, but aren't married or aren't filing a joint tax return, which parent claims the dependent on their tax return?

If both parents live together and don't file a joint tax return, they just need to agree on which parent will claim the child on their tax return. The agreement can be written or verbal. If there's not an agreement, then the following "tiebreaker" rules are applied:

• If one of the parents isn't legally the child's parent, the child will be the dependent of the legal parent.
• If the parents didn't live together for the entire year, the child will be the dependent of the parent with whom they lived for most of the year.
• If the child lived with each parent for the same amount of time during the year (for example, if the family lived together for the entire year), the child will be the dependent of the parent with the highest adjusted gross income (AGI).