A dependent is someone you support: meaning you've provided at least half of the person's total needs for the year (food, shelter, clothing, etc.). Typically, a dependent is a child or other relative.
- Must be a US Citizen, US national, or a resident alien
- Must have a tax identification number (social security number, individual taxpayer identification number, or adoption taxpayer identification number)
- Can file their own tax returns, and even be married, but must not have filed a joint return unless it was only to claim a refund
Specifically, to claim a child as a dependent:
- Must have lived with you for half the year
- Must be related to you (son, daughter, stepchild, foster child, brother, sister, stepbrother, stepsister, or a descendant of those)
- Must be 18 or under at the end of the year (or under 24 if a student who was full-time for at least 5 months of the year)
- Must be younger than your (or your spouse if married filing jointly), unless the child is disabled
For other relatives or an unrelated person:
- Must not have income over $4,050
- Must not be a qualifying dependent of another person (you can't claim the person if someone else could)
- Must be related to you or have lived with you all year as a member of your household.