Nolo explains that a parent is not required to pay child support until he is established as a legal parent, by a paternity test, court order or other legal means. An unmarried father who signs an acknowledgement of paternity pays child support, even without his name on the birth certificate.
Nolo states that a father must pay child support once he acknowledges paternity or if he is the presumed or equitable parent. A father who is married to the child's mother is presumed to be the child's biological father: As the legal father, he must pay child support.
Depending on the state, someone who invites the child into his home and holds the child out as his own may be required to pay child support. A step-parent may be obligated to support a child if he legally adopts the child, according to J Rank.