What Is a Paternity Lawsuit and How Does It Work?

A paternity lawsuit is a court case that legally establishes who a child’s father is when that question hasn’t already been settled by marriage or a signed acknowledgment. It ends with a court order naming a specific man as the legal father, and that order is what unlocks child support, custody, visitation, inheritance, and benefits. Without it, a biological father has no legal standing and a child has no legal claim on him, no matter what a DNA test shows informally.¹

When a Lawsuit Is Actually Necessary

Court isn’t the only way to establish paternity, and it isn’t the first step most parents should take. Federal law requires every state to run a voluntary acknowledgment program, usually offered at the hospital when the child is born and available afterward through vital records offices until the child turns 18.²¹ If both parents sign the form after receiving written and oral notice of what it means, the acknowledgment carries the same legal weight as a court order. Either parent can rescind within 60 days; after that, undoing it generally requires proving fraud, duress, or a material mistake of fact.

A lawsuit becomes the right tool in three main situations: the alleged father refuses to sign an acknowledgment, there’s genuine disagreement about who the biological father is, or a man who believes he’s the father can’t get the mother to cooperate. If both parents agree, skip the court route.

Who Can File

Mothers file most paternity cases, usually because they need a child support order, health insurance for the child, or formal recognition for inheritance and benefits purposes.

A man who believes he is the biological father can file on his own when the mother denies his paternity or shuts him out of the child’s life. Filing is what gives him legal standing to ask for custody, visitation, or any voice in decisions about the child’s education and healthcare.

State child support agencies file paternity cases regularly. When a mother applies for public assistance such as TANF or Medicaid, federal law requires her to cooperate with the state in identifying the father.³ The state’s interest is recovering the public funds spent on the child’s care. In some jurisdictions, the child can also bring the action through a guardian or representative.

How the Case Moves Through Court

Filing and Service

The case opens with a petition filed in family court, usually titled something like “Petition to Establish Paternity” or “Petition to Establish Parentage.” It identifies the child, names the alleged father, and asks the court for a legal determination.

The other party then has to be formally notified through service of process. A process server or sheriff physically delivers the petition and a summons. The summons sets the deadline for a written response, typically 20 to 30 days depending on the jurisdiction.

The Response

The respondent has three options: admit paternity, deny it, or ignore the papers. Admission lets the court move straight to entering a paternity order. Denial sends the case to genetic testing. Ignoring it is the costliest choice, and it deserves its own section.

If You Ignore the Petition

If the alleged father is properly served and does nothing, the court can enter a default judgment naming him as the legal father without any DNA testing at all. A child support order can be issued at the same time.¹

Overturning a default judgment later is difficult. You would need to go back to court, show a legitimate reason you didn’t respond (such as never actually receiving the papers), and typically still submit to DNA testing. Judges are not sympathetic to people who threw the paperwork away. If you’ve been served, respond before the deadline even if you dispute being the father. The response is where you dispute it.

DNA Testing

Federal law requires states to order genetic testing in contested cases when any party requests it and backs the request with a sworn statement alleging or denying paternity.² A technician swabs the inside of the cheek of the mother, child, and alleged father. No needles.

Modern testing compares genetic markers and produces a probability of paternity, with 99 percent or higher the standard for a positive match. Courts treat those results as conclusive. The lab work itself takes only a few business days, but the full process from court order to admissible results usually runs four to six weeks because of scheduling and chain-of-custody requirements.

A court-admissible test runs about $300 to $500. Over-the-counter home kits are cheaper but won’t be accepted in court because they lack a verified chain of custody. When the state orders the test, the agency pays upfront and can recoup the cost from the father if paternity is established.² In private cases, the court usually assigns the cost to whichever party requested the test or to the losing party.

What the Final Order Actually Does

Once the court enters a paternity order, the legal relationships lock into place.

For the Child

The right to receive financial support from both parents.
The right to inherit from the father under state intestacy laws.
Eligibility for Social Security survivor benefits, veterans’ benefits, and similar programs tied to the parent-child relationship.
Access to the father’s health insurance and the ability to be named a life insurance beneficiary.
Access to the father’s family medical history.

For the Father

The order gives him legal standing to seek custody or visitation and to participate in major decisions about the child’s education, healthcare, and welfare. Without that order, a biological connection by itself gets him nothing in court.

The matching obligation is financial. Child support is typically addressed in the same proceeding or shortly after, calculated under state guidelines, and may include contributions toward health insurance and a share of childcare and medical costs.¹

For the Mother

She gains a formal child support order backed by court enforcement. If the father doesn’t pay, the state can garnish wages, intercept tax refunds, and use other collection tools. In exchange, she has to comply with whatever custody or visitation schedule the court sets. Once the father has a court order granting him access, she cannot unilaterally deny it.

Timeline and Costs

An uncontested case where the alleged father agrees and no testing is needed can finish in a few weeks. A contested case with DNA testing, hearings, and follow-up on support and custody realistically runs several months. Disputes over the marital presumption or challenges to an earlier paternity finding can stretch longer.

Expect the following cost categories, which vary by jurisdiction:

Court filing fees from $0 (some jurisdictions waive them in paternity cases, especially those filed by the state) up to about $300.
Service of process at roughly $50 to $150 through a process server or the sheriff.
DNA testing at $300 to $500 for the standard three-party test.
Attorney fees, optional but often worth it in contested cases, charged hourly or sometimes as a flat fee.

If the state child support agency brings the case, the mother typically pays nothing. For private cases, many courts allow fee waivers for people who can show financial hardship.

If the Mother Was Married

If a child is born while the mother is married, every state presumes her husband is the legal father. The biological father, even if everyone knows who he is, is not the legal father until the marital presumption is formally overcome in court, usually with DNA evidence. Some states impose strict time limits on challenges to the presumption. A biological father who waits too long can lose the ability to establish his parentage, and a husband who learns he isn’t biologically related may still owe child support if he doesn’t act within the window. The clock varies by state, so getting local legal advice early matters.

Challenging Paternity After It’s Established

Paternity can be revisited after it’s been set, but the openings are narrow.

For a voluntary acknowledgment, either parent has 60 days to rescind without giving a reason. After that, the only path is proving fraud, duress, or a material mistake of fact.² Later discovering you aren’t the biological father is not automatically enough if you signed voluntarily after being informed of the consequences.

For a court-ordered determination, a man seeking to overturn it generally has to file a motion backed by grounds such as new DNA evidence, fraudulent test results, or a fundamentally flawed original proceeding. Many states cap how long you have, and courts weigh the child’s need for stability heavily. Even when a paternity finding is terminated, past child support payments are almost never refunded; the obligation going forward ends, but courts consistently hold that clawing back prior payments conflicts with the child’s interests.

Federal law requires states to allow paternity to be established any time before the child turns 18, and some states go further.¹ The deadline to challenge an existing order is a separate and usually much shorter clock. If you think a paternity order was entered incorrectly, move quickly.

1
Office of Child Support Enforcement. Chapter 3: Establishing Fatherhood
2
Office of the Law Revision Counsel. 42 USC 666 – Requirement of Statutorily Prescribed Procedures
3
Office of the Law Revision Counsel. 42 USC 654 – State Plan for Child and Spousal Support