A paternal grandparent test and a maternal grandparent test use the same laboratory method. What differs is which side of the family you test and which parent is missing from the picture. If the child’s father is unavailable, you test his parents (the paternal grandparents). If the child’s mother is unavailable, you test her parents (the maternal grandparents). Everything else, from how samples are collected to how results are read, follows the same logic.
This guide explains the difference in plain terms, shows who needs to take part in each version, describes what a grandparent test can and cannot prove, and lists the questions to settle before you order.
TL;DR
- Paternal and maternal grandparent tests rely on the same autosomal DNA comparison. The only practical difference is which side of the family you sample.
- Test the paternal grandparents when the alleged father cannot take part. Test the maternal grandparents when the mother cannot.
- Grandparents share about 25% of a grandchild’s DNA on average, so results are less direct than a parent-child test. Adding the other parent usually strengthens them.
- Home kits are for personal knowledge. Courts and government agencies require a witnessed chain-of-custody that home collection does not provide.
- Our Home Grandparent DNA Test costs $139. Standard orders take 7 to 10 business days from order to results.
Table of Contents
- What “paternal” and “maternal” mean in a grandparent test
- How the science works
- Paternal grandparent test: when the father is unavailable
- Maternal grandparent test: when the mother is unavailable
- Side-by-side comparison
- How strong are grandparent test results?
- Our perspective on choosing a side
- Home testing and what it cannot do
- Practical steps before you order
- Costs and options at a glance
- Common misconceptions
- FAQ
- Sources
What “paternal” and “maternal” mean in a grandparent test
Paternal grandparents are the parents of a child’s father. Maternal grandparents are the parents of a child’s mother. In everyday conversation the words describe family sides. In a DNA test they describe which biological parent’s DNA you are trying to reach through an older generation.
The test does not look for a special “paternal” or “maternal” signature. Each child receives one set of 23 chromosomes from the mother and one from the father, and each of those sets is a shuffled mix of that parent’s own two sets. According to the National Human Genome Research Institute, children get one complete set of chromosomes from each parent. The lab simply asks whether the child’s DNA pattern fits the pattern you would expect from the grandparents being tested.
That is why a question like “which type of grandparent test is more accurate” has a short answer: neither side is inherently better. Accuracy depends on who is tested, not on whether they sit on the mother’s or the father’s side.
How the science works
Autosomal DNA does the work
Relationship testing relies mainly on autosomal DNA, the 22 pairs of chromosomes that are not sex chromosomes. A person inherits half of their autosomal DNA from each parent, and on average about 25% from each grandparent. A review in PubMed Central describes autosomal DNA as the primary standard for proving biological relationships, and notes that when a parent cannot be tested, grandparentage tests may be used but often give lower confidence levels and may call for additional evidence.
The 25% figure is an average. Because chromosomes are recombined at random each generation, one grandchild may carry slightly more DNA from one grandparent than another. The Genome Institute’s fact sheet makes the same point: inheritance comes from random recombination across all four grandparents, and there is no biological category of a “stronger” grandparent.
Why Y-DNA and mitochondrial DNA are not the answer
People often assume paternal grandparents can be tied to a grandchild through the Y chromosome, and maternal grandparents through mitochondrial DNA. Both markers exist, but they are lineage markers. A forensic evaluation in PubMed Central explains that they are inherited from just one parent and remain largely unchanged across generations. That means they cannot separate a father from his brother, or a mother from her sister, so they are poorly suited to confirming who a particular child’s parent is.
A Y-line test can also only apply to male-line relatives. If you want to learn more about that narrower approach, our article on Y-STR testing and the paternal line covers when it fits and when it does not.
Paternal grandparent test: when the father is unavailable
A paternal grandparent test is the usual choice when a man may be a child’s father but cannot or will not give a sample. He may have died, be out of contact, or be unwilling to take part. His parents each passed about half of their DNA to him, so a child who is his biological son or daughter should carry a share of DNA that traces back to them.
Who takes part in a typical paternal grandparent test:
- The child.
- One or both of the alleged father’s parents.
- The child’s mother, when she is available.
Including both grandparents gives the lab more of the alleged father’s genetic contribution to compare against. Including the mother lets the lab separate the DNA the child got from her from the DNA that must have come from the father’s side. Without her, results can still be informative, but the comparison has less to work with.
Maternal grandparent test: when the mother is unavailable
A maternal grandparent test mirrors the paternal version. It is used when the mother cannot be tested, for example when she has died, or when a family is trying to confirm that a child is the biological grandchild of the woman’s parents. The tested adults are the mother’s parents, with the child and, if possible, the father.
In practice maternal tests come up less often than paternal ones. Questions about a child’s mother are usually settled at birth, while questions about a father are more common. If the question is simply whether a woman is a child’s biological mother and she can be sampled, a direct maternity test is more straightforward than testing her parents. Our Home Maternity Test Kit is priced at $129, compared with $139 for the grandparent version.
Side-by-side comparison
| Paternal grandparent test | Maternal grandparent test | |
|---|---|---|
| Who is missing | The alleged father | The child’s mother |
| Grandparents tested | The father’s mother and/or father | The mother’s mother and/or father |
| Other participants | Child, ideally the mother | Child, ideally the father |
| Core method | Autosomal DNA comparison | Autosomal DNA comparison |
| Average DNA shared with child | About 25% per grandparent | About 25% per grandparent |
| Stronger when | Both grandparents and the mother join | Both grandparents and the father join |
The pattern is symmetrical. The strength of either test grows with the number of close relatives who contribute samples.
How strong are grandparent test results?
A parent-child test compares a child with someone who passed on half of their DNA. A grandparent test compares a child with someone who passed on about a quarter, and through an intermediate person who is not in the room. That extra step is the reason confidence levels are usually lower than for a direct paternity test, and why a grandparent test is generally a second choice when the parent can be tested.
Three practical points follow:
- Test the parent if you can. For paternity, the same PubMed Central review notes authorities typically look for at least 99.5% certainty, and grandparentage often provides less.
- Add every close relative you can. A second grandparent or the child’s other parent narrows the comparison.
- Expect a clear exclusion to be easier to reach than a clear inclusion. If the tested grandparent shares none of the expected genetic markers with the child, that is strong evidence against the relationship. A match is read as a probability of relationship, not as an absolute.
If you want a walkthrough of what the numbers in a report mean, see our guide to reading a grandparent DNA test report.
Our perspective on choosing a side
Most families who contact us about grandparent testing do not start by asking whether the paternal or maternal side is better. They start with a practical problem: one person cannot take part, and someone else has agreed to help. Our advice follows from that.
We suggest working backward from who is actually available. If a grandparent is willing and the missing person is the father, the paternal test is the right fit. If the missing person is the mother, the maternal version is. The science is the same, and what changes the outcome is how many relatives you can include. That is why our test selection tool asks about the whole family, not only the grandparent, before it recommends a kit.
We also encourage families to be realistic about what a grandparent test gives them. It can bring clarity to a private question, but because grandparents share about a quarter of a child’s DNA on average, it is a less direct measure than a parent test. When a parent can be sampled, we usually point people toward that simpler option, which can also cost less. Our home paternity kit is $79, and our home grandparent kit is $139.
Finally, we want families to understand early that a home test is not a substitute for the kind of testing used in court or by government agencies. Knowing that before you buy avoids frustration later.
— Dr. Todd Lewis
Home testing and what it cannot do
A home grandparent test lets family members collect cheek swabs on their own schedule and mail them back. For a family that wants an answer for personal reasons, that convenience is often the point. Our kits include a prepaid return shipping envelope, and our lab analysis uses up to 28 markers.
The limit is formal use. Self-collected samples have no witness confirming who gave them. The AABB 2024 technical report separates tests performed with a chain-of-custody from those without one, and the lack of a witnessed collection is what keeps non-chain-of-custody results informational. The U.S. State Department also describes DNA relationship testing procedures for visa cases that follow its own controlled process, which a home kit does not replace.
We do not offer court-admissible testing at this time. If your question involves a custody case, a support order or any government filing, speak with a family law attorney before testing, and ask them what kind of collection the court or agency will accept. Our article on why consumer kits fail in court explains the difference in more detail.
It is also worth separating a relationship test from consumer health or ancestry products. The CDC cautions that direct-to-consumer genetic tests are not diagnostic and are not meant for legal or medical decisions. If a result raises a health concern, a genetic counselor is the person to see, not a family relationship report.
Practical steps before you order
- Name the question. Are you trying to confirm paternity, maternity, or whether a child is your grandchild? If a parent can be tested, start there.
- List who can take part. Write down which grandparents, parents and the child are willing and reachable. Their availability decides whether you need the paternal or maternal version.
- Check the relationship line. Make sure the grandparents you plan to test are the biological parents of the missing parent. A stepparent or adoptive parent will not share DNA with the child in the way the test expects.
- Decide on timing. Lab processing takes 2 to 3 business days once samples arrive. A standard order takes 7 to 10 business days from order to results, because shipping time is included. Our Next-Day Results option is available for $100, and details are on our test finder page.
- Collect carefully. Do not eat, drink or smoke shortly before swabbing, and label each swab with the right person’s name. Mixing up swabs is the most common avoidable error.
- Plan for the result. Talk through, ahead of time, how the family will handle an unexpected outcome. Test results can affect relationships.
For a broader look at the case where a father is not available, our guide on the best grandparent test when the father is unavailable covers the decision in more depth.
Costs and options at a glance
Prices below are as published on our site.
| Test | Price |
|---|---|
| Home Paternity Test Kit | $79 |
| Home Maternity Test Kit | $129 |
| Home Grandparent DNA Test | $139 |
| Home Aunt/Uncle DNA Test Kit | $139 |
| At-Home Full Sibling DNA Test Kit | $139 |
If you are not sure which kit suits your family, our guided test finder asks a few questions about who is available and recommends the most accurate and affordable option. You can also browse every kit on the home DNA test collection, including the Home Grandparent DNA Test at $139.
Common misconceptions
“Girls inherit more from their paternal grandmother.” This idea appears in popular articles, but the Genome Institute’s explanation of inheritance does not support a rule that favors one grandparent in that way. Chromosome recombination is random.
“Paternal grandparents can be proven through the Y chromosome.” Y-DNA passes only along the male line and is shared by close male relatives, so it does not identify a specific child’s father. See the forensic review cited above.
“A grandparent test is as conclusive as a paternity test.” It is useful, but as the PubMed Central review notes, grandparentage tests often provide lower confidence than direct parent testing.
“Any DNA kit can answer a family question.” Ancestry and health kits are designed for other purposes. Relationship testing compares specific genetic markers between named people.
FAQ
Is a paternal or maternal grandparent test more accurate?
Neither is more accurate by nature. Both compare autosomal DNA, and grandparents on either side share about 25% of a grandchild’s DNA on average. Accuracy improves when more relatives are included, such as both grandparents and the child’s other parent.
Can I test just one grandparent?
Yes, in many cases a single grandparent can be tested. Results are generally stronger when both grandparents on the same side take part, because the lab has more of the missing parent’s DNA to work with. If only one is available, adding the child’s other parent helps.
Do I need the mother’s sample for a paternal grandparent test?
It is not always required, but it is recommended. Her sample lets the lab identify which parts of the child’s DNA came from her, which sharpens the comparison with the paternal grandparents.
Will a home grandparent test be accepted in court?
No. Home collection has no witnessed chain-of-custody, and courts and government agencies generally require one. We do not offer court-admissible testing at this time. Ask a family law attorney which kind of testing your situation requires.
How long do results take?
Lab processing takes 2 to 3 business days after your samples arrive. A standard order takes 7 to 10 business days from order to results. Next-Day Results is an optional $100 add-on.
Sources
- National Human Genome Research Institute fact sheet
- Review of relationship testing standards, PubMed Central
- Forensic value of Y chromosome and mitogenome evidence, PubMed Central
- AABB 2024 Relationship Testing Technical Report
- U.S. Department of State: DNA Relationship Testing Procedures
- CDC: Taking a genetic test on your own
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