Why Don’t I Match My Cousin?

no cousin

I receive this question regularly from people who have taken one of the autosomal DNA tests and who expected to match a cousin, but don’t.

Of course, the Jeff Foxworthy in me wants to say, “Because he’s not your cousin,” but fortunately, I never let my inner Jeff Foxworthy out in public.

Actually, that’s often their biggest fear – that they are uncovering a very unpleasant family secret – but Jeff Foxworthy aside – that’s generally not the case.

Let’s take a look at why.

According to Family Tree DNA’s FAQ on the subject, combined with the percentage of DNA shared with each type of cousin, we find the following.

Relationship to You Likelihood of a Match % of DNA Shared
1st Cousin (common grandparents) 100% 7-13
2nd Cousin (common great-grandparents) >99% 3-5
3rd Cousin (common great-great grandparents >90% .3-2
4th Cousin (common ggg grandparents) >50% <1%
5th Cousin (common gggg grandparents) >10% Sometimes none detectable at match threshold
6th Cousin (common ggggg grandparents) <2% Often none detectable at match threshold

If you don’t match your first cousin, then you need to start thinking about Jeff Foxworthy or you’re simply extremely lucky, or unlucky, depending on your perspective.  Buy a lottery ticket. 

In all seriousness, if you don’t match a first cousin, consider having your sibling (or parent) or your cousin’s sibling or relevant parent test as well.  In some cases, two people simply inherit different DNA and even though they don’t match each other, they do match other people in the same family. 

However, if you’re going to go down this path, be prepared that the answer may be that you really aren’t genetic cousins.  By the time you get to this point, you’ve already peeked into Pandora’s box though, so it’s kind of hard to shut the crack and pretend you never looked. 

Another option for determining whether or not you really match that cousin is to download both of your results to GedMatch.  The testing companies have pre-set match thresholds that determine what is and is not a match.  That’s a good thing, but what if your match is just slightly under that threshold, and there aren’t other relatives to test?  GedMatch allows you to match at very small segment levels that would generally be considered population matches and not genealogy matches.  

Judy Russell had the perfect example of just this situation in her Widen the Net blog.  Her mismatch was with a 3rd cousin.  According to this the chart above, she stood a greater than 90% change of matching, but she didn’t, so she’s in the special 10%.  And that 10% gets left wondering.  Fortunately, Judy had tested aunts, uncles and another first cousin, and her cousin who did not match her did match them. 

The moral of this story is:

  • Ignore Jeff Foxworthy when he starts to whisper in your ear, at least initially
  • Test as many family members as you can
  • Don’t jump to conclusions
  • Utilize third party tools like GedMatch if necessary
  • Understand that if you test enough family lines, you will eventually find an undocumented adoption someplace

74 thoughts on “Why Don’t I Match My Cousin?

  1. Hi Roberta
    This is Melba McGee Niemuth. When my DNA results came back, (I am NA (C), my younger brother, Robert (Bob) McGee (Q) didn’t show up. Neither did my 1st cousin, nor two of my 3 second cousins. The 3rd cousin that did—his mother ‘s father was a brother to my grandma. Melba

  2. Hi,

    I was running my husband’s matches and found a Roberta (Buster) Estes on his matches. So, I am wondering if you could give me an area where the Estes might have come from so that I could check for a pattern with terms to location, such as where the came from and where they landed.

    Thank you,
    Tia Gray

  3. Hi Roberta,
    I hope you are enjoying your trip. I have a couple of comments:
    From above: “In all seriousness, if you don’t match a first cousin, consider having your sibling (or parent) or your cousin’s sibling or relevant parent test as well. In some cases, two people simply inherit different DNA and even though they don’t match each other, they do match other people in the same family. ”
    If you don’t match your first cousin or even your second cousin, then there is no gray area, you are not genetically related. The ambiguity doesn’t occur until you get to the third cousin level, as in Judy’s example. It is impossible for first cousins to simply inherit different enough DNA from their shared grandparents to not be detected as a match by FTDNA’s Family Finder or 23andMe. (This is likely true at AncestryDNA as well.)

    Also, the chart isn’t broad enough. Second cousins can legitimately share much less DNA than 3%. (I need to update the Wiki, I see.) I have proven full second cousins in my family study who only share 1.07%, 1.15%, 1.3%,1.62%, 1.65% and 1.87%. I have tested many additional family members to confirm the actual relationship.

    • Does this mean that every person then has to inherit some autosomal dna from each of their 4 grandparents? How about siblings inheriting completely different dna from one of their parents? I understand it would be very unlikely but it is actually not possible? I wish I had paid more attention in school 😉 Thanks!

      • Yes, each person has to inherit some DNA from each grandparent. Siblings each get exactly half of their parents DNA. I’ve never seen a scenario where 2 children get the exact opposite half of millions of DNA locations.

  4. I love this explanation Roberta! & also the one on triangulation! This is so true & happened to us. Two cousin kit comparisons (1st cousins) was just not enough for us to find our surname matches, though we matched each other big time. We then then found a 4th cousin to test. I don’t match him, but my 1st cousin does. Between the 3 kits, we have found descendants of 5 children out of 8 , of our brick wall 3rd great grandfather. I don’t think that is so bad for a beginning. The sad thing is how many relatives refuse to test.

  5. Roberta, In trying to verify who is not the father of my cousin we have this information. J and B are 1st cousins on their maternal side, their shared cM is 779.51. J and B mother’s were sisters who married twin brothers, Ju and Jo. Since J and B have a set of common grandparents on each side, shouldn’t their shared cM be approximately double what it is? Are these FF results enough to make this conclusion. The paternal grandparents are P&A and the maternal grandparents are G&E. There are reasons other than DNA to support a NPE for J and Ju.
    We have a child, all 1st cousins, from each of 4 siblings, the two sisters above, 1 more sister and a brother(JA) who have tested. Of the 4 siblings, only the brother was able to be tested and all are now now deceased(the siblings). The other two 1st cousins, V and B. V shares cM 992 with J and 788 with B. N shares 816 with J and 814 with B. Ja is father of V and they share 3382. Ja is Uncle of J, N, and B, they respectively share, 1763,1549, 1658 with Ja.

  6. Roberta, I found the link to “percentage of DNA shared” above after I posted regarding my cousins J and B and the father of J. I think that answers my query, J and B would be “double cousins” and because their shared DNA is not double what they share with other 1st cousins, not possible for Ju to be the father of J. Still would be great to have a confirmation, thanks for all of the insight you post.

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  8. I want DNA Test match of my uncle or cousin.my father is dead in 28 years ago.now what i can do?my grandfather is two married.first marriage my grandperents.2nd married my uncle mother.

  9. Hi, Roberta–I recently asked this question on another blog, but still am in the dark: A known 1C matched via FF; that 1C also matched ICW another match (that I confirmed on paper and who would be a 3C to both). When I run the matrix tool, all three are related, so far so good, but then when I compare them in the chromosome browser, the 3C is does not show any overlaps with the 1C unless I drop it down to 3cM and then 1cM. That in and of itself would not be surprising, but what I am not clear about is why the relationships would even be picked up with the ICW and matrix tools if there was not enough shared DNA as reflected on the chromosome browser. I assume this is due to the tools analyzing the data differently? I administer both kits and performed all tools with each.

    • The matrix just tells you THAT you have a common match with that person, not where. The browser tells you where that match is. That’s why you need both tools. The browser also can’t pick up below the match threshold of 20cM total and 7.7cM in at least one segment, but the browser does when you drop the thresholds. So your ultimate test is the browser.

  10. Hi there our cousin test came back 28 percent probable inconclusive I’m left wondering if we are please shed some light only one parent could also be tested thankyou in advance

  11. I have a half sister, 27.9/53 which I was told recently is a first cousin. Can that be true or another lie that has been told for the past few years? Mom took the sisters child and raised her as her own. Know it happens.

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  13. I have 2nd cousins and we all have the same great grandparents on both sides. My mom and dad have the same 1st cousins but my parents are not kin. How kin am I to my cousins and what dna test do we take?

  14. I have a match with a first cousin (Paternal)
    But a 3rd cousin once removed and another 3rd cousin show as a match to each other but no match to me or my first cousin.
    On Chromozme 10 me and my first cousin are 63875333-102814750= 41.4 cm

    3rd cousins match Chromozome 10 -65939157-99268810 =37.14 cmm

    Does this not show we are connected as we all have the above match on Chromozome 10

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  16. I tested with Family Tree and a cousin with Ancestry.
    His mother and my father share the same surname.
    Gedmatch shows we have no shared DNA but we have a common match with someone 5 generations ago.
    My question is, how do we attempt to figure out where, if possible, our common match fits into our ancestry.

      • Thanks for your quick response. I will rephrase.
        I run my one to many and a match shows up with 5.2 Gen and 10.1 Cm as the Total Cm.
        I run my cousin’s one to many and the same match shows up as 4.7 Gen with a total of 21.7 Cm.
        My cousin and I do not share any DNA.
        These results are all from Gedmatch because I tested with Family Tree and my cousin with Ancestry. I cannot test with Ancestry because I do not reside in the USA.
        I was wondering how we (my cousin and I) have the same person as a match but we do not seem to share DNA. If these results are correct, where would our common match fit in on our ancestry?

      • If you and your cousin do not share DNA segments, but you both match someone else, that could simply mean that other person shares a different segment with both of you separately, just not the same segments. It could be from the same ancestor or different ancestors.

  17. My Dad’s sister married my Mom’s 1/2 brother. There is some question as to whether my Mom is actually my Grandfather’s child. Can we find out by testing a double cousin or would we need to test my Mom’s posible full sisters kid? We know they had the same Mother but Dad is the question.

  18. Please help I have a DNA match with 300 cM and was wondering if that is a second cousin. I also share 156 cM with her daughter. I don’t know who my father is so It’s difficult. Trying to find out. We are thinking it’s on her dad’s side of the family. How can we narrow it down.

    So wanted to know who I am connected to

  19. Hi my name is Sherri I am adopted last year I found my maternal family I didn’t get to meet my mom just my sister so she helped fill in some of the gaps which is wonderful she did not know who our moms dad was or our grandmas dad was but i found them all good on my grandmas side but my moms dad is a little frustrating I found out that my moms dad is a davidson because of dna cousins Amount of Shared DNA
    207 centimorgans shared across 10 DNA segments her name is sheri she is my 1st cousin 1xr her father has 9 siblings this is another 1stc 1xr her dad is sheris fathers brother n10177 thats all i have for her name Amount of Shared DNA
    450 centimorgans shared across 16 DNA segments i also have a second c 1xr that does not come up in my dna just in my tree and a DNA circle my great grandmas brother is her grandfather but we dont share any dna why

  20. Do you know of any new algorithms being worked on that will help identify and clarify currently unreported distant matches ?

    Thank you,


  21. Regarding my previous questions.
    My non match cousin’s aunt recently tested and she matches with me, she also matches at the normal level with my non match cousin.
    I suppose that is the luck of the DNA draw.

  22. I don’t know much about DNA testing. Will it tell me if 2 female maternal 1st cousins share the same maternal grandfather?

  23. Hi. getting a little confused with all this DNA matching. I have loads of 3rd cousins and 4ths, 6th. etc., one 2nd cousin and a 1st cousin. Now then what’s confusing me is the X-Match. I am an X Match with my first cousin who is female I am male. I thought that I get the Y from my dad to make me a bloke and the X from my mother, and in the case of a female she gets the X from her dad to make her female and another X from her mother, so if you are going to compare two Xs then the X that I have is from my mother and the Xs that my cousin has are from her father and mother, note that her father is my fathers brother. A little help here at confused.com would be appreciated.

  24. I just recently found out that the man that I thought was my father for the last 32 years is really not my father. It has been said that my biological father and the man whom I thought was my father are cousins. The family believes that my biological grandmother, and my grandmother for the last 32 years are half sisters, through extramarital affairs by who I believed to be my great grandfather. I had a DNA test with the man I thought was my father, and it came back with a 0% chance of him being my father. Being that there was no DNA match at all, does that mean that we are not related at all, which would also mean that the rumors of whom I thought was my great grandfather are not true, and my two grandmothers are not really sisters?

  25. Hello, I had my wife’s dna tested through AncestryDNA to find out the identity of her father. We got a hit on a first cousin most likely on her father side but this first cousin we found her full blooded sister is coming up as a distant 5th to 8th cousin. How is this possible?

    • That sounds very unusual, but Ancestry does strip out some segments. I would suggest that all people involved transfer either to FTDNA or Gedmatch, both are free, and neither strip segments, and see what the relationship is there.

      • Thank you this is what my next step was going to be but now I will definitely push for this to be done.

  26. I have a related puzzle, and since this thread is still active, I hope you can help. My problem is that I have found a man on 23andMe who has a 5.02% match to my father on 18 segments. He also matched my father’s sister, though that match is slightly lower, around 4.14%. I have created a family tree for him, and can find no overlap at all, going back to at least 1900. 5% is a pretty strong connection, but I’m at a loss for where it comes from.

    So, is there a table somewhere that gives percentage DNA matches for extramarital relationships? In other words, to get 5%, should I be looking at cheating grandparents or greatgrandparents or even plain old adoptions? Am I pretty much out of luck without testing various cousins to track the match? My father does have a presumed second cousin (2.41%) on his fathers side (can’t find the exact relationship, but we have matching names, towns, and memories), and she doesn’t match this other guy at all. Would that imply the relationship is through my father’s mother?

    I hope this made sense! Thanks in advance!

  27. Curious, As far back as I can remember, people would say, my brother& father, resemble, an athlete. At the time, I didn’t really see it. My grandmother, became somewhat, obsessed with this guy , having lost her husband, my grandfather, ( I never met) at a young age, she saw, this athlete, in my grandfather, father& brother. As I got Older, I did to. He resemble, my father 4sure, Scary Part, he didn’t resemble my brother, He was/Is his TWIN!! My own, mother didn’t believe, a photo, was this guy, she thought it was my brother, her OWN son. The mannerisms, looks, build, sarcastic ways, are dead on!! Its Freaky!! We share the same last name, and, recently found out, whether it be coincidence or not, our grandfather , have the same name as first , middle, last. Not all that common of a name. Did he have another child, we didn’t know of?? My father, did 23&Me, as we suspected, his ethnicity, was dead on. As Myself/Brother are 1st generation, US citizen. My ? is there any way 2 get a DEFINITIVE answer, as to the relation, if any? Because, of his sports celebrity status, everything, I tried, is private?. He looks, more like my brother, in a heartbeat, than my own father . It’s kind of indescribable, I guess. Any suggestions, on how we can, find out 4sure? My grandmother/grandfather, are both deceased, and I now wonder, Why was my grandmother, so SMITTEN, by this guy? Watching every game, he played?? Not the norm, 4 a grandmother of 12!! I was 26, when she passed&any secret she had, went with her. I don’t know, if its even possible to prove so, again, if he was an “Average Joe” maybe, a little easier, do you recommend, a procedure on how to go about, with a celebrity athlete? Appreciate any help!! Thanks÷

  28. Hello,
    I hope that this is still an open thread. I am new the the DNA thing so allot of things go over my head. My mom and I did our DNA testing and it was great however we are not matching up to my mom’s first cousins on her dad’s side of the family. We weren’t’ matching with one cousin so we decided to have another one of my moms first cousins get tested and we are not matching up with her either. Now I have my mom all worried that her dad isn’t her dad. I’m not sure what to do from here. I did get one cousin to do GEDmatch and she didn’t show up as a match in that either. I’m feeling really bad about freaking my mom out and I’d like to know what is the next step. Both of her parents have passed away her sister is a half sister not my grandpas daughter so that doesn’t help to get her tested. Any help you can give would be greatly appreciated.
    Thank you so much!
    A daughter that really stepped into it and opened Pandora’s box!

  29. I left a question on October 17th about what to do when you find a 5% DNA relative, but no connection can be found between the two trees. What would you do if you encountered such a problem?? ANY thoughts would be helpful.

  30. Had my DNA done but don’t match my father’s Mother’s side of the family at all. Her family is all French, and my DNA came back Irish, Wales, Great Britian at 75%, nothing about being French. I’m very discouraged.

    • Ethnicity is only an estimate. DNA testing is illegal in France. Use the matching available at most vendors and see what comes up that way. Ethnicity only scratches the surface of what’s available.

  31. My husband was adopted and we just received his AncestryDNA testing back, showing:
    Possible range: Parent, Child – immediate family member
    Confidence: Extremely High
    Relationship: [intiails] is your Father

    Is there any doubt if this is the conclusion? Is there a reason to take a paternity test?

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