A paternity test is a DNA test that determines whether a specific man is the biological father of a child. It works by comparing genetic markers from the child’s DNA to those of the potential father, and modern tests are more than 99.99% accurate when a match exists. Paternity tests can be done after birth with a simple cheek swab, or as early as eight weeks into a pregnancy using a blood draw from the mother.
How a Paternity Test Works
Every person inherits half their DNA from their biological mother and half from their biological father. A paternity test looks at specific locations in the DNA, called STR loci, where genetic patterns vary from person to person. The lab compares the child’s DNA profile at these locations to the potential father’s profile. At each location, the child should share one matching pattern with the father. If the patterns consistently match across all tested locations, paternity is confirmed. If they don’t match at multiple locations, the man is excluded as the biological father.
The lab calculates something called a Combined Paternity Index, which compares the likelihood that the tested man is the father against the likelihood that a random, unrelated man from the same ethnic group could produce the same match. When paternity is confirmed, this probability typically exceeds 99.99%. When the man is not the biological father, the probability drops to 0%, and the report states he is excluded.
Cheek Swabs vs. Blood Samples
Most paternity tests use buccal swabs, which are soft swabs rubbed along the inside of the cheek to collect cells. This is painless and takes about 30 seconds per person. Blood draws are also used in some settings, particularly for prenatal tests. There is no significant difference in accuracy between the two sample types. DNA is DNA regardless of where it comes from, so cheek swabs produce results just as reliable as blood.
At-Home Tests vs. Legal Tests
There are two main categories of postnatal paternity tests, and the distinction matters depending on what you plan to do with the results.
At-home (peace of mind) tests cost between $100 and $300. You order a kit, swab the cheeks of the child and potential father at home following the included instructions, and mail the samples to a lab. Results are private and sent directly to you. However, because nobody verified who provided the samples, these results cannot be used in court or for any legal proceeding.
Legal paternity tests cost between $400 and $800 or more. The key difference is chain of custody: samples are collected at a certified facility where a trained collector verifies each person’s identity (usually with a government-issued photo ID), photographs participants, and documents the entire process. This documented chain of custody ensures the samples haven’t been tampered with or swapped, which is what makes the results admissible in court.
The actual lab analysis is identical for both types. The price difference reflects the supervised collection process, documentation, and legal certification of results.
Prenatal Paternity Testing
You don’t have to wait until a baby is born to establish paternity. A non-invasive prenatal paternity test (NIPP) can be performed as early as the eighth week of pregnancy. The test works because fragments of fetal DNA circulate in the mother’s bloodstream during pregnancy. A provider draws blood from the mother and takes a cheek swab from the potential father. The lab then isolates the fetal DNA from the mother’s blood sample and compares it to the father’s DNA profile.
Because this test only requires a standard blood draw from the mother, it poses no risk to the pregnancy. Older methods involved collecting amniotic fluid or placental tissue, which carried a small risk of miscarriage. The blood-based NIPP test has largely replaced those approaches. Prenatal tests are the most expensive option, ranging from $1,000 to $2,500 or more.
What the Results Mean
A paternity test report will include one of two conclusions. If the man is the biological father, the report will state he “cannot be excluded as the biological father” and list a probability of paternity at 99.99% or higher. The phrasing sounds cautious, but in practice this is a definitive confirmation.
If the man is not the biological father, the report will state he “is excluded as the biological father” with a probability of 0%. This is equally definitive. There is no gray area or inconclusive middle ground with properly collected samples from both parties.
Legal Rights Affected by Paternity
Establishing paternity through a legal test has significant consequences. It directly affects child custody arrangements, visitation rights, and child support obligations. Once a court recognizes a man as a child’s legal father based on a paternity test, he gains the right to seek custody or visitation, and can also be ordered to pay child support. The child, in turn, gains inheritance rights and access to the father’s medical insurance and benefits.
If a paternity test later contradicts a previous finding (for example, through retesting with updated methods), a court may modify or vacate the original paternity order. This can change existing child support, custody, visitation, and inheritance arrangements. Courts typically require a legal test with documented chain of custody before making any of these determinations. An at-home test result, no matter how clear, won’t hold up in family court.
Cost and Timeline Summary
- At-home test: $100 to $300. Results are private and not court-admissible.
- Legal test: $400 to $800+. Requires supervised collection with verified identity. Court-admissible.
- Prenatal test: $1,000 to $2,500+. Can be performed from the eighth week of pregnancy onward.
Some states allow courts to order paternity tests in custody or child support disputes, in which case one or both parties may be responsible for covering the cost. If you need results for a legal matter, it’s worth confirming with your local family court what specific requirements they have before choosing a testing provider.