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Strategies for Finding Biological Grandparent Using DNA

Are you interested in learning how to use your DNA to find out the identity of your biological grandparents?  No matter how old you are, or whether or not you believe your grandparents to be living, it’s possible to use your DNA results to determine who they were. 

Strategies for Finding Biological Grandparent Using DNA

If you are interested in family tree research, knowing the names of your biological grandparents is an important step to being able to build your family tree further back into history.  In this post, I’ll share some strategies that you can use to better understand your DNA results and find out who your biological grandparents are.

To identify grandparents using DNA, your DNA matches are key

Many people who do DNA tests are initially interested in their ethnicity estimate and then realize later how much information can be learned from their DNA lists.  In order to identify biological relatives, including grandparents, our DNA match lists are key. 

I’m assuming that if you are looking for grandparents, then you already know who your parents are.  People who are descended from our grandparents will be as closely related as first cousins, or half-first cousins, depending on the circumstances. 

Relatives who are descended from the parents of our grandparents are our second cousins.

It’s most helpful to have first, second, and third cousin DNA matches to help us identify the possible names of our grandparents.  Most people in the United States will have several DNA matches that fit into these categories. 

Even so, it’s possible to identify grandparents using only fourth cousin DNA matches, so don’t worry if you don’t end up with many close DNA matches.

Since DNA matches are so important for figuring out who our most recent ancestors were, we need to make sure that we have as many DNA matches as possible to work with.  This is why I highly recommend considering downloading your raw DNA data from your testing company and uploading it to the following sites:

I realize that DNA testing and paying fees for DNA uploads can add up, but if you can manage it, you should try to test with the following two companies, if you haven’t already.  These companies have the largest DNA databases of DNA testers (more than 15 million people between the two of them), and there is the best chance that you’ll find your closest relatives on these sites:

  • Ancestry DNA
  • 23 and Me

The goal is to try to have access to as many DNA matches as possible to make sure that we are on the right track with our grandparent research.  Once you feel good about then number of DNA matches that you have access to, move on to the next step.

Click here to buy the Understand Your DNA Results Ebook

Are your grandparents on your DNA match list?

Before we look at other DNA matches, it’s important to check to see if your grandparents are actually on your DNA match list.  Depending on how old you are, it’s totally possible. 

Grandparents typically share between 1300-2300 centimorgans with their grandchildren.  There are other relationships that fall within this same range and they include half-siblings, aunts, uncles, nieces, and nephews.

Most DNA testing companies don’t have a separate “grandparent” category on your match list, primarily because there is no way for the testing company to tell you whether or not the person is your grandparent, aunt, uncle, or a half-sibling. 

On Ancestry DNA, for example, a grandparent is likely to show up in the “Close Family” category.   On My Heritage, DNA matches include more nuanced relationship possibilities. 

Grandparent matches on the site might show up as a “Grandfather/Half-brother” or “Grandmother/Half-sister”.

This means you should check through your closest matches to see if there is anyone who shares between 1300-2300 centimorgans with you. 

It’s also important to note that there have been verified cases of grandparents sharing slightly less than 1300 cMs with their grandchildren – just something to keep in mind if you spot someone who shares, say, 1150 cMs with you and you just can’t figure out who they are.

Find out who the parents and grandparents of your closest matches are

If you are sure your grandparents aren’t already on your DNA match list, the next step is to figure out who the parents and grandparents of your closest matches are.  This is especially true if you have DNA matches that are related to you in the immediate family, close family, or first cousin category. 

If you don’t have any matches that fall into those categories, no worries.  Use your second and third cousin matches for this exercise.

We want to identify the parents and grandparents of our closest DNA matches because there is an excellent chance that their parents or grandparents are actually our grandparents.  This is especially true if you have DNA matches related at a second cousin distance or closer.

It’s important to note that the predicted relationship given to you by the DNA testing company is usually not the actual genealogical relationship that you have with a DNA match.  To figure out exactly how you are related to someone, and who their ancestors might be to you, you’ll need to look at their family tree and the amount of centimorgans that they share with you.

If you have several first cousin matches or closer who also have family trees on the site, then you have identified several people who could be your grandparents.

Note:  If you believe that one of your grandparents is “misidentified” in your family tree (i.e. your entire family believes that one person is your grandparent, but you are sure that they are not based on DNA results) due to a NPE or other circumstance, you can skip to the next section which explains the logic used to use 2nd-3rd cousins to identify grandparents.

I’ve written two posts that I think might help you in figuring out how your DNA match is related to you and who their closest ancestors are:

Find out who the great-grandparents of your second cousin DNA matches are

Since we want to know who your grandparents are, and we have moved on to second cousin DNA matches, we will now need to extend our focus to the great-grandparents of our second cousin DNA matches.  Many of our second cousin DNA matches might know who their great-grandparents are, and some of them might have family trees. 

Occasionally, our second cousins might have only small family trees attached to their results or profiles, and we might need to do a little research to extend their trees back a generation or two.

Fortunately, our second cousin matches are still pretty closely related, so we don’t have to do too much research to determine who their great-grandparents might be.

If you see a pattern among your second cousin matches and spot the same great-grandparents in a few family trees (and your second cousin matches don’t seem to be siblings – this is important), then you might have spotted your great-grandparents. 

The next step is to figure out who the children of your great-grandparents are.  Research where they lived, who they married, and who their children are, who their children married.

Check for geographic areas in common with where your grandparents were born, ages of children where your parents were born, dates of death, and other clues that can help you eliminate someone as a possible grandparent (i.e. parent to your parent).

To determine where you fit into your possible grandparent’s tree, see how all of your matches are connected

If you have several close or “close-ish” matches, I like to try to figure out how everyone is connected with each other.  This can help me spot patterns and figure out the structure of the family. 

You could do this by adding them to your family tree, if you already know how they are connected to you, or drawing it out on a piece of paper.

If you are having a hard time sorting your DNA matches into groups of people who are related to each other, you might be interested in learning about the Leeds method. This method can help you sort your matches into groups that are likely descended from the same common ancestor, upon which time you can use family tree information to find the ancestor they all share in common.

Don’t ignore your close DNA matches

If you spot someone who doesn’t seem to match what you know about your tree, or you don’t seem to fit into their tree, don’t ignore this.  You are most definitely closely related to your close DNA match, and if you ignore a match that doesn’t seem to “match” what you think you know, you might miss something very important about your ancestry. 

This is especially true if you are searching for close ancestors – some people only have a couple close family or first cousin matches show up, and if you ignore one of them, you might overlook the key to locating the identity of your grandparents.

Using third and fourth cousins to find identity of grandparent

If you don’t have any second cousin DNA matches or closer, you can still use your DNA results to identify your grandparents.  Full disclosure: this is a more difficult strategy.

You will share great-great grandparents with your third cousins (assuming that they are genealogically third cousins) and great-great-great grandparents with your fourth cousins. 

Each person has sixteen great-great grandparents and 32 great-great-great grandparents, and you will need to make sure that you have figured out who these ancestors are for as many of your third and fourth cousins as you can.

This can take a while, but once you have done it, you will most definitely spot patterns.  You will be able to sort you third and fourth cousins into groups of people who are all descended, or seem to be descended, from a particular ancestor or pair of ancestors.

Once you’ve established which group each DNA match belongs to (or most of them), then you have likely identified your great-great grandparents and your great-great-great grandparents.

As I said before, this is a lot of work, but for some people this is the only way to figure it out.  So, stay with me.

Once you know who your great-great grandparents are, you can research their children and great-grandchildren in order to see where your parent might fit into their tree – use the same clues as I mentioned above in order to see where the connection is most likely.  This will require a lot of research and patience, but the results are worth it.

I posted this above, but it’s useful so here is it again.   I’ve written two posts that I think might help you in figuring out how your DNA match is related to you and who their closest ancestors are:

Test your family tree to see if you have identified the right family for your grandparents

There is a really cool way to test your family tree to make sure that you have identified the correct family for your grandparents. This is similar to making a mirror tree, which you can only do on Ancestry and only if you have tested your DNA with Ancestry

If you have a family tree on Ancestry, and have tested your DNA there, too, you also need to attach your DNA results to your family tree.

Even if you don’t yet know for sure which sibling in a particular family is your grandparent, you can still test your theory (based on your research) about your grandparent’s immediate family. 

If you are descended from the couple that you have identified as your great-grandparents, and you have built your tree a few generations further back on the lines of those great-grandparents, you should receive “Common Ancestor Hints” as verification that you have other, more distant, relatives who are also descended from those same ancestors.

This isn’t a foolproof method, as our family trees are complicated, but it is a good way to see if you are on the right track or are completely off-base.  It’s also a good way to help you decide between two couples that seem like they could both be your ancestors.  Occasionally, this will also help you learn more about your ancestry.

Sometimes, you might not be able to figure out exactly who your grandparent was using only DNA

Every once in a while, we might find that even though we are able to identify the parents of our grandparents (i.e our great-grandparents), we can’t seem to narrow down which of their children is our grandparent. 

I have found this is most common when searching for a grandfather (it’s exceptionally easy for a man to have a child that he doesn’t know about or that his family is unaware of). 

For example, you might be sure that Mr. and Mrs. Smith are your great-grandparents because you are related to several of their other descendants, but you can’t figure out if your grandfather is Bob or Billy because neither of them seem to have had children.


I hope that this post has given you some ideas about how to use your DNA results to identify your grandparents.  If you have any questions about something that you read here, or if you would like to share your own experience searching for biological grandparents, I would love to hear from you in the comments below.

Thank you for reading the Who Are You Made Of blog today 🙂

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Terry Savage

Thursday 5th of January 2023

I am feeling very frustrated that I cannot pinpoint who my father is even though AncestryDNA has connected me to who my great grandmother is and her mother, my great-grandmother. I applied with DNAngels and they said they were going to have to take a pause on the search for my birth father. I have tried writing down a family tree but it just gets lost when I have to go to extra pages. Are there any big ancestry charts that I might purchase for this task?

Violet faumuina

Tuesday 31st of May 2022

I never knew my grandfather or his family all I know is he’s my mothers dad but wasn’t raised by him I just wana know if she has any siblings my mother passed and she never told me his name I just know he’s fr Niue wow that’s not much

Janice Hussey

Thursday 2nd of September 2021

These articles have been so helpful! I am trying to learn who my great grandfather was. We have a name that has been passed along through the years. My father’s mother (GM) was conceived and born in England in 1896. My GM emigrated to the United States, and joined her mother’s sisters and brothers in Maine.

Her mother (my GGM) later followed with a new husband and children. She never married my GM’s father. She married and had children soon after my G’s birth. He died. She again remarried and had another child. Then she also emigrates to Maine, USA from England.

My brother and uncle (father’s 1/2 brother, same mother) have tested on 23 & Me and Ancestry. We have constructed extensive family trees also. My GG IS OUR BRICKWALL. I have DNA matches in England that I am trying to determine my connection to. Many could be my GG sibling’s or cousin’s children.

We are curious if my GG had other family we are related to.

Thank you for sharing your expertise! Jan

Alexandra Cloud

Wednesday 9th of December 2020

Hi Mercedes, many thanks for getting into the 4th cousin matches, I mostly have these, with very few closer matches, especially on Ancestry (have tested or uploaded my DNA to all the big genealogy sites, I think). I am looking into a hunch of my late mother's that her father was not her biological father, so I'm looking for a potential biological grandfather (BGF). None of her father's family descendants have matched on DNA. I can easily separate my own parents' DNA matches based on ethnicity (my mother was Jewish), but I'm finding it difficult to separate the DNA matches on my mother's side. Both my parents are deceased and my only shared sibling half brother (mother's son) won't test, but his son has (and that match aligns with the expected cM overlap according to the shared centimorgan v4.0 table/tool). So I'm putting my half-nephew together with myself as sharing my mother as a MCRA. Then I have my mother's known 2C, and my known 2C1R as having my great-great grandparents as our MCRA. Both the 2C and 2C1R appear to be one step closer (based on shared cM) than predicted by the WATO tool - so I'm wondering whether my mother's parents were related, e.g. first cousins, so I'd have 6 great-greats instead of 8, and this might account for the increased cM overlap? Also when I model one of my maternal grandmother's first cousins as my BGF, there's a 5th-8th cousin DNA match on the potential BGF side that fits the WATO tool prediction. Hope this makes sense. Trying not to jump to conclusions at this stage, but do you think this is the appropriate approach re matches, and apart from trying to find other matching descendants, what else could I be trying? I'd love to find a way to combine all my DNA match data on one tree - do you have any recommendations for this? Thanks for all your work in making genealogy and genetics a bit easier to understand. best wishes, Alexa

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