Parents are married. If the child's parents file separate returns, use the return of the parent with the greater taxable income. Parents not living together. If the custodial parent is not considered unmarried, use the return of the parent with the greater taxable income. For an explanation of when a married person living apart from his or her spouse is considered unmarried, see Head of Household in chapter 2.
Parents are divorced.
Custodial parent remarried. Therefore, if the custodial parent and the stepparent file a joint return, use that joint return. Do not use the return of the noncustodial parent. If the custodial parent and the stepparent are married, but file separate returns, use the return of the one with the greater taxable income. If the custodial parent and the stepparent are married but not living together, the earlier discussion under Parents not living together, applies.