the question is who under the tax laws is legally entitled to claim the the child. The legal documents granting you custody don't mean anything when it comes to the tax laws
these are the rules
Qualifying child – and eligible to be claimed as a dependent the rules are:
- Must be a US citizen, resident alien or national or a resident of Canada or Mexico
- Related to you - son. daughter. stepchild, eligible foster child, or a descendent of my of them; brother, sister, half-brother, half-sister, stepbrother, stepsister or a descendent of any of them. Adopted child if legally adopted or an individual lawfully placed with the taxpayer for legal adoption. Eligible foster child is one placed with the taxpayer by an authorized placement agency or by judgment decree or order of any court with jurisdiction.
- Must be either: a) under 19 at the end of the year and younger than the taxpayer claiming or b) under 24 at the end of the year and a full-time student. A full-time student is one who is enrolled full-time in school (but not online or correspondence schools) during any part of 5 calendar months during the calendar year or took a full-time course of institutional on-farm training under the supervision of an accredited agency.
- Same principal abode as you for more than ½ the tax year. Temporary absences are ignored.
- Hasn’t provided over ½ their own support. Taxable or nontaxable scholarship payments are ignored in determining support.
- Hasn’t filed a joint return – unless there is no tax liability.
- If a qualifying child of more than one person there are tie-breaker rules
if they and you qualify to claim the child based on the above tax laws, under the tie-breaker rules, you as the parent have priority.
since they already claimed the child you would have to file by mail.
