Determining the answer to the seemingly simple question "Who is the father?" is not as straightforward as you might think. Different circumstances give rise to different legal rules.
Acknowledged father. An acknowledged father is a biological father of a child born to unmarried parents, for whom paternity has been established by either the admission of the father or the agreement of the parents. An acknowledged father must pay child support.
Presumed father. If any of the following are true, a man is presumed to be the father of a child, unless he or the mother proves otherwise to a court:
In some states, any of these presumptions of paternity is considered conclusive, which means it cannot be disproven, even with contradictory blood tests. In Michael H. v. Gerald D., 491 U.S. 110 (1989), the U.S. Supreme Court upheld California's presumed father statute as a rational method of protecting the integrity of the family against challenges based on the due process rights of the father and the child.
A presumed father must pay child support.
Equitable parent. The law has changed a great deal in the last decade, and now in quite a few states, a spouse who is not a legal parent (biological or adoptive) may be granted custody or visitation under the notion of equitable parent. Courts apply this concept when a spouse and child have a close relationship and consider themselves parent and child or where the biological parent encouraged this relationship. If the court grants an equitable parent custody or visitation, then the parent will also be required to pay child support. This type of parentage decision occurs frequently in cases where same-sex couples are parenting together.
Alleged father. An unmarried man who impregnates a woman is often referred to as an alleged father, or sometimes simply as an unwed father. An alleged or unwed father will be required to pay child support if a court determines or he acknowledges that he's the father; in addition, an alleged or unwed father has the right to visitation with his child and may seek custody.
Stepfather. A stepfather is the spouse of a legal mother and is not also the biological father of the woman's children. A stepfather is not obligated to support the children of the woman to whom he is married unless he legally adopts the children.
A paternity action, a court suit filed to have a man declared the father of a child, can be brought by either the mother or the father. Paternity actions are sometimes called establishment hearings, filiation hearings, or parentage actions.
Most paternity actions are initiated by welfare officials who provide TANF (Temporary Aid to Needy Families) to the mother and are required by law to seek reimbursement from the father. The mother must cooperate in these proceedings; failure to do so can result in a reduction or loss of her TANF grant.
Today, blood and DNA tests can affirmatively determine paternity with a 99.99% accuracy and can rule out paternity with 100% accuracy.
If paternity is established following a paternity action, the court will order the father to pay child support and grant him custody or visitation rights.