Most people understand that both parents have an obligation to pay for the things that a child needs and that child support is often ordered to ensure that the child has the resources he or she needs. Fathers may even accept this responsibility voluntarily.

Even if they are not married, they may publicly declare that the child is theirs and their responsibility. They may sign an affidavit of paternity. However, if they later find out that the child is not actually biologically theirs, the process may not be simple to try to remove the father from the obligation of supporting the child.

In some situations, fathers may not be able to be reimbursed for child support they paid for a child that is not theirs. Even worse, they may still be required to pay child support for this child until he or she reaches 18 or finishes school. Whether the father will be relinquished from this responsibility depends on a number of factors, including when the child was born, how paternity was established and where a child support order is in place.

Children Born During the Marriage

When a child is born to a mother who is married, the law in most states presumes that the husband is the father. Likewise, if a child is born and the mother later marries her partner, the law may presume that the husband is the father. In some states, there is an irrefutable presumption of this. In these states, if a child is born during the marriage, the husband is legally the father even if a DNA test later shows someone else is the father. In other states, this presumption can be overcome if the father actively rebuts this presumption. However, there is usually a very limited deadline by which a husband can refute paternity, such as two years after the child is born. If he does not rebut this presumption, he loses the right to later challenge it and can be obligated to support the child.

Children Born to Unwed Parents

If a child is born while the parents are unwed, the man may agree to have is name on the birth certificate. In some instances, this is enough to obligate the father to support the child. In other situations, a court can determine that a person is the father because he has told others that he is the father and held himself out as the father.

Child by Consent

Some jurisdictions will look to the conduct of the parents. There is a public policy preference to have a person named as the father of the child rather than the child being considered fatherless. If a man has acted like a parent and permitted the child to believe he was the father, some states may find this to be sufficient evidence that the man is the father. The father may then be required to pay child support.

DNA Tests

If a father refutes paternity and is in a time window when such argument can still be made, he may establish through DNA testing that he is not the father. However, many states have determined that a DNA test alone is insufficient to vacate a paternity determination. Family law courts base decisions on what is in the best interest of the child, and this is usually to continue to have financial support from someone even if he is not actually the father.

Challenging Paternity

If a father wants to challenge paternity, he will usually submit this challenge to the court that entered the relevant order, such as a child support order, judgment of divorce, paternity establishment or judgment of legal separation. Each state has different guidelines on how paternity can be contested and when there is defaulted paternity. There may be challenges to default judgments, such as lack of notice of the proceeding. The father may be able to reopen the judgment. However, many jurisdictions only allow reopening of a judgment for a finite period of time, such as within one year of the initial entry. After that time, there may be only limited exceptions for when the judgment may be reopened, such as fraud, misrepresentation or good cause.

In some jurisdictions, the father may be able to seek to set aside the judgment based on fraud. In this type of action, the father would likely have to prove that the mother knew that he was not the father and intentionally deceived him. This may be difficult to establish as the mother may have simply been wrong about paternity. Simply saying that the mother knew and not showing proof of this would unlikely result in reopening or winning the case. It may even be necessary to legally prove who the actual father is. The court is often unwilling to revoke a paternity acknowledgment if another man is not willing to accept this responsibility. The court is focused on the financial stability of the child.