Gedmatch Generations

One of the tools on Gedmatch that is very useful but which causes some confusion is the column headed “Gen”, which means “Generations”. The number in this column means the estimated number of generations back to the common ancestor shared by you and your match. Whilst we easily understand that 2 generations back to a common ancestor means we are cousins, 3 generations back means we are second cousins and so on, but what confuses many people is how can you have in-between numbers like 2.6, 3.9, 4.1?

This number is to be understood as a guestimate or guideline that shows roughly how far back you might start looking for your common ancestor. To quote genealogist Kerry Scott, the generation estimates are “not etched in stone – they are etched in sand at best!” This is due to the random way that DNA is inherited between each generation – it is very common, once you get beyond a couple of generations, for a segment of DNA to remain intact and be passed down over several generations without changing. This means that the number of generations given with your match might also be exactly the same as that shown with your match’s parent or grandparent!

Another problem comes when you might be three generations back to a common ancestor and your match is from a closer generation and they are only two generations back to the same common ancestor. How do you work that out?!

So I had a look at the known connections I have with my genetic cousins who’ve uploaded to Gedmatch and this is the range of how Gedmatch calculated the generation distance to the most recent common ancestors and then I give the actual relationships. As you can see, the further distant the common ancestor, the more varied are the possible relationships.

Gen 1
Well, that’s easy – it’s always going to be a parent-child relationship

Gen 1.2
Oddly, this is always a sibling relationship

Gen 1.4
Half-sibling
Uncle ~ niece
Grandparent

Gen 1.5
Uncle ~ niece
This makes sense: the common ancestors for my uncle are his parents, which is 1 generation, but for me, his niece, it is my grandparents, 2 generations. Therefore, the Gedmatch Generation is calculated as being between 1 and 2 = 1.5

Gen 1.6
Uncle/aunt ~ niece/nephew
Grandparent

Gen 1.9
1C (first cousins), whose common ancestors are their grandparents, which is 2 generations

Gen 2.2
1C (first cousins)
1C1R (first cousins once removed)

Gen 2.3
1C1R (first cousins once removed)

Gen 2.5
1C1R (first cousins once removed)
Again, this makes sense: my cousin is a generation older than me, his grandparents, which is 2 generations, are my great-grandparents, which is 3 generations. Therefore, the Gedmatch Generation is calculated as being between 2 and 3 = 2.5

Gen 2.6
1C1R (first cousins once removed)
2C (second cousins)

Gen 2.9
2C (second cousins)

Gen 3.0
2C (second cousins)
This is the ideal scenario, with the common shared ancestors for me and my match both being 3 generations back.

Gen 3.3
2C1R (second cousins once removed)

Gen 3.5
2C1R (second cousins once removed)
Again, this makes sense: my second cousin is a generation older than me, her G-grandparents, which is 3 generations, are my GG-grandparents, which is 4 generations.Therefore, the Gedmatch Generation is calculated as being between 3 and 4 = 3.5
3C (third cousins)
2C2R (second cousins twice removed)
Here we have a case of our common ancestors being my G-grandparents, 3 generations, but these ancestors are my matches GGG-grandparents, 5 generations: a difference of two generations between me and my match

Gen 3.6
2C1R (second cousins once removed)
3C (third cousins)

Gen 3.7
2C1R (second cousins once removed)
3C (third cousins)
3C1R (third cousins once removed)

Gen 3.8
2C2R (second cousins twice removed)
3C (third cousins)

Gen 3.9
3C1R (third cousins once removed)

Gen 4.0
3C (third cousins)
This is the ideal scenario, with the common shared ancestors for me and my match both being 4 generations back.

Gen 4.1
2C1R (second cousins once removed)
2C2R (second cousins twice removed)
2C3R (second cousins three times removed)
This is quite an unusual because our shared common ancestors are my GGGG-grandparents, 6 generations back, but my match’s shared common ancestors are only his G-grandparents. That’s a difference of three generations, even though my match is just 10 years older than me! This is because I am descended from the eldest child of our common ancestor, but my match is descended from the youngest child, who was 25 years younger; and likewise my ancestors were the eldest of young parents, but my cousin’s parents and grandparents had children late in life, which resulted in this apparent shift of three generations even though me and my match are in the same present-day generation! Yes, just think about it for a moment 😀
3C1R (third cousins once removed)

Gen 4.2
2C1R (second cousins once removed)

Gen 4.3
3C (third cousins)

Gen 4.4
2C2R (second cousins twice removed)
3C (third cousins)
3C1R (third cousins once removed)
3C2R (third cousins twice removed)
4C (fourth cousins)
4C1R (fourth cousins once removed)

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53 Responses to Gedmatch Generations

  1. Chris says:

    Thankyou for explaining that. Makes sense now.

    Like

  2. cassmob says:

    Thanks! This a great help.

    Like

    • gengenaus says:

      Thanks Pauline – I’m happy if it’s helpful for you. By the way, I really like your blog and enjoyed listening to your interview on Genies Down Under podcast last year 🙂

      Like

  3. Diane says:

    Thank you Cate. It makes such sense now.

    Like

    • gengenaus says:

      You’re welcome, Kerryn. By the way, I like your website about your Irish ancestors – I have a great interest in Irish Australian history – my focus is on South Australia 🙂

      Liked by 1 person

  4. Pamela Lydford says:

    Ithink I understand. Pamela

    Like

  5. Lauren says:

    Thanks. Think I will print this out for reference.

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  6. Courtney McAllister says:

    Thank you for this information. Can you provide information on how the descendants of half siblings (sister and brother) would show? The potential descendants are both males and their Estimated number of generations to MRCA = 2.5. After discovering this DNA connection, I am trying to determine the specific connection and from a chronological standpoint, it would make sense if one of the connection’s Mother and the other’s Father were half siblings. Is there a way to determine if this theory is correct? Or would I need to go an additional generation back in the case of half sibling descendants with a 2.5? Thanks in advance for your assistance!

    Largest segment = 72.6 cM
    Total of segments > 7 cM = 443.3 cM
    18 matching segments
    Estimated number of generations to MRCA = 2.5

    Like

    • BrendaW says:

      I can give you comparison with my family. I have tested and my half sister has tested and we’ve tested our children as well. Mine are the girls and hers are the boys.

      Megan and Jason:
      Largest segment = 48.3 cM
      Total of segments > 7 cM = 503.9 cM
      19 matching segments
      Estimated number of generations to MRCA = 2.4

      Megan and Jonathan:
      Largest segment = 54.2 cM
      Total of segments > 7 cM = 399.4 cM
      16 matching segments
      Estimated number of generations to MRCA = 2.6

      Amanda and Jason:

      Largest segment = 56.3 cM
      Total of segments > 7 cM = 564.1 cM
      20 matching segments
      Estimated number of generations to MRCA = 2.3

      Amanda and Jonathan:
      Largest segment = 60.1 cM
      Total of segments > 7 cM = 532.0 cM
      18 matching segments
      Estimated number of generations to MRCA = 2.4

      Like

  7. donegalroots says:

    Thanks Cate That was very helpful. I would think that when there is endogamy or multiple relationships to several grandparents involved this can throw off these estimates. For example, I have a known 4th cousin with whom I share 124 cM with the longest segment being 40 cM. Gedmatch estimates the relationship to be 3.4, which would be 2C1R. This cousin has 3 ancestors in common with me. He comes from a small Catholic community in rural Ontario, Canada, where there was a lot of cousin marriages, back in the 1800s.

    Like

  8. Lynda says:

    Just made a chart with this info for future reference.

    Like

  9. Sharon Rowe says:

    Thank you, thank you!

    Like

  10. Ali says:

    Hi

    I would be very grateful if you could tell me what a half aunt/half niece would be. I measure mica 1.9 but don’t know if my match is a 1sr cousin or half niece. My father is either her uncle or her grandfather. Many many thanks if you could help me. Ali

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  11. Leigh says:

    Hi, I’m so lost. Gen has me at 1.6 with a person that is my mother’s first cousin .yet that person shares a paternal uncle with me. It was said her father was also my father. I tested with alledged father’s brothers son and got 1.6 too. We’ll known gen.said it’s like a have twin father’s but they wasnt. It just gets messier. The family doesn’t want me to be their fathers daughter. Tested with same persons full brother and he was higher in cms etc with me then the sisters. I’m female. Smh. Blessings. So confused and lost in this

    Like

  12. CathyB says:

    This is interesting. But the 1.0 generation can also be identical twins, not just parent/ child. Or it could be yourself, with 2 different kits. As an example, I compared my own Ancestry kit to my own 23andMe kit — self to self — and got a match of 3587 cM, 22 segments, and estimated # of generations to MRCA = 1.0

    Like

    • gengenaus says:

      Thank you Cathy for your perceptive comments – yes, you’re quite right, particularly regarding identical twins which present some interesting problems for genealogists using DNA.

      Like

  13. Renee M Boudreau says:

    May want to add/edit; 1.9 Gen to MRCA can also be Half Niece or Nephew
    New found half nephew of my Mom matches at 1.9 gens on Gedmatch….

    Like

  14. genealyn says:

    Interesting analysis. You are lucky to have been able to place so many of your gedmatch matches.

    Like

  15. eva rojas says:

    I am totally confused and am trying to figure all this out with help of my daughter. Can I compare with my 4th cousins from ancestry or do I have to start with what they give me?

    Like

  16. BrendaW says:

    I have tested and two of my full siblings have tested, a first cousin has also tested and shows as first cousin to myself and my two siblings and we also have a 2nd cousin to all of us who has tested. She shows as a second cousin to myself and my first cousin, which she is. My sister’s distance is 3.6 and my brother’s is 3.8 (same as my daughter). We also have a 2nd cousin, 1X removed. She didn’t upload to Gedmatch but on Ancestry her cMs fit where they should with me, my sister, my first cousin but not with my brother. The 2nd cousin and the 2nd cousin 1x removed are descended from my grandfather’s sister so I’m guessing that they may have inherited more DNA from great grandparent and my brother from the other.

    Like

  17. Gendigs says:

    1.5 is also grandparent; approx 25% of dna. Percentage of dna passed may be more transparent for descendancy.p

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  18. embee says:

    Me and a supposed 7th cousin are losing our minds. Our cm match on gedmatch is about 40 cm which seems to be way too high for 7th cousins, and it gives us a 4.1 generation match, which is obviously much earlier too. But, a descendant from the same couple has a 26 cm match to me, and is descended through a different child of the couple than my 7th cousin. Is it possible we could have this high a match after so many generations? Tables for 7th cousin give numbers like range= 0-10 cm, average=7 cm. And, we are much higher than that….. thanks alot, MB

    Like

    • gengenaus says:

      Yes, 40cMs is too high for 7th cousin, unless you are from a family with known endogamy issues – that is, families who have a long history of cousins intermarrying, such as Ashkenazi Jewish or Syrian-Lebanese or Polynesian, as such like. The other explanation might be that you match that person on two separate branches of your family and you have yet to find where that other match might be. I have had this in my own family tree where a 4th cousin on my father’s side was also a 6th cousin on my mother’s side. This happens a lot in colonial families.

      Like

  19. DB says:

    Is this chart of generations a definite list. Could someone who is 1.5 be a half sibling or only a niece or nephew? The chart says 1.4 is half sibling and uncle niece for 1.5.

    Like

    • gengenaus says:

      No, this is definitely not a ‘definite list’ 🙂
      This is just the range I have found in my own research, just from my own DNA results and matches.
      So, a half sibling and/or uncle-niece will fall within the range of 1 – 2, depending on how much shared DNA there is. I recently worked on a client case where we were trying to figure out that exact type of question: Is this relationship a cousin or is it half uncle-nephew? But within out solving the case by means of traditional genealogy research, it was not possible to determine from DNA alone. That is, there is no definitive way of proving a relationship based on the amount of DNA alone or of the suggested generation distance – you need to sleuth it which is the ‘correct’ relationship by using other methods. BUT, DNA is where you start 🙂

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  20. Tonia Porter says:

    Can you tell me where gen 4.6 would fall on your list? I have 2 DNA cousins through Gedmatch that triangulate with me. But we can’t find our MCRA. Knowing the generation(s) to look at would help greatly!
    Thanks!

    Like

    • gengenaus says:

      It’s important to remember that the further back in generations, the more factors influence the range of possible relationships. Gen 4.6 should be treated like I’ve mentioned for my results of 4.4 – there is a great number of possible combinations. Also, at that far back, it might also be influenced by others factors such as cousins intermarrying which will make your common ancestor appear to be closer than it actually is. I have a gen 4.2 match and we can’t find the common ancestor but we know they come from an English village where many families intermarried over the centuries, which means our actual common ancestor might be 7 or 8 generations back!

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  21. Karin T says:

    Thanks for the explanation! Very helpful, as gedmatch can be confusing. One thing, my grandmother shows as 1.5 generations – a bit confusing, as she’s 2 generations from me. Any thoughts?

    Liked by 1 person

    • gengenaus says:

      I just checked my daughter’s matches to her grandparents and I’ve added that relationship to the ones listed in my blog. Yes, you would expect it to say 2 generations but for some reason that I can’t explain, it does seem to come up as around 1.5 – a glitch in the system?

      Like

  22. jerrypittsjr says:

    Could you please let me know what 3.1 is? Does this mean they share the same great-grandparents?

    Like

    • gengenaus says:

      Hi Jerry,
      Yes, Gen 3.1 would suggest common ancestors who are great-grandparents. However, this is not a ‘rule’ – it depends on other factors such as the possibility of a ‘half’ relationship (only sharing one common ancestor), or if the two people being compared might be a generation apart themselves (the match is considerably older or younger than the person whose results are shown), or if there is endogamy issues (in communities where there are cousins intermarrying, which ‘doubles’ the amount of shared DNA and therefore shows up as a closer generational relationship in Gedmatch than is actually the case)

      Like

      • jerrypittsjr says:

        Thanks for the explanation. The common issue I am encountering is like this 3.1 who my father shares 207.7 cM Total 33.2 Largest is in my tree as a 5th Cousin. Is it common to be that far off. While we certainly had a lot of cousins marrying cousins in Covington County, Mississippi, I also have a known Graves line and my father’s paternal great-grandfather is unknown. I do have 4 Y-DNA37 Graves. One at a genetic distance of 3 and three at a genetic distance of 4. Two of these matches run through this same line as my known Graves line which runs through my grandmothers, mother. So I have both paternal and maternal, and since my paternal is not known at the moment, my tree readings are picking up the known relationship, which seems to be a longer route to the MRCA. A few more examples:
        Total Largest Gen
        DP – 124.9 48.2 3.4 In Tree as 4th Cousin
        BD – 109.0 23.6 3.5 In Tree as 5th Cousin
        BD – 102.6 42.6 3.6 In Tree as 5th Cousin
        RB – 64.1 16.9 3.9 In Tree as 5th Cousin 1x Removed
        Most of my Graves matches are accurate according to the chart, and I have many of them. These all seem to be older matches, 5th – 7th Cousin range. It’s these higher cM matches that I thinking may be coming from this unknown great-grandfather.

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  23. jeanine says:

    I’m a little confused. You have 3.9mrca= 3c1R, but 4.2mrca = 2c1r. I would think that 4.2 would be further away than the 3.9?

    Like

    • gengenaus says:

      Hi Jeanine,
      These results are just what I have found in my own personal DNA research. They are not a set of rules – just how the DNA dice rolled in my own family 🙂

      Like

  24. Syvellia says:

    Hello,this information is quite informative. I do have a question about info that is missing. What is a 1.7 generation match. I have someone that showed up in my matches and I am not sure how we are matched.

    Like

    • gengenaus says:

      Hi Syvellia,
      These figures are reporting what I’ve found in my own personal DNA research. There are many factors that will influence what the actual relationship is for an indication of 1.7 generations. Depending on the age difference between you and your match, the indication would be the match is your aunt/uncle or niece/nephew or grandparent or grandchild. It is also possible for the match to be a half-sibling or a first cousin. But at any rate, this person is certainly a close family member.

      Like

  25. nolancestry says:

    Great info. I tested with my great uncle (my grandfather’s brother) and we are 2.3 gen. in another matter, have you observed that two men might have closer gen matches than a man to a woman? My mom matches 5.1 to a certain person but her brother matches 3.8 to same person. My mom and brother are full siblings. That seems like a lot of leeway.

    Like

    • gengenaus says:

      Hiya – yes, that does seem some leeway, but it is definitely not related to gender, which has no bearing at all on autosomal DNA results. However, it is not uncommon to get wide variances between siblings when the distance is more than three generations – it is just the luck of the roll of the DNA dice if you inherit enough DNA from a more distant ancestor to show up at all! The more distant the ancestor, the wider variation in the Gedmatch ‘guestimates’ of generational distance.

      Liked by 1 person

  26. Michael Harris says:

    I can confirm that MRCA=1.0 when run against my identical twin. Here are our numbers:
    Largest segment = 263.5 cM

    Total Half-Match segments (HIR) = 3583.2 cM (100.0 Pct)
    Estimated number of generations to MRCA = 1.0

    107352 SNPs used for this comparison.

    100.0 Pct SNPs are full identical

    Comparison took 0.39703 seconds.
    Ver: Sep 12 2017 16:38:56

    Like

  27. Jessica Wright says:

    What is gen 4.7?

    Like

  28. L.D. Johnson says:

    Did a GEDMatch one to one comparison with a cousin I’m pretty sure is a 3rd cousin twice removed, but MRCA estimation of 4.8 really threw a curve ball as to whether we would be considered 3rd cousins twice removed or fourth cousins. Same thing with a another cousin that is 4.9 gen of our most recent common ancestor.

    Me and My Cousin D.B.
    Largest segment = 17.5 cM
    Total of segments > 7 cM = 17.5 cM
    1 matching segments
    Estimated number of generations to MRCA = 4.8

    Me and My Cousin C.R.
    Largest segment = 15.8 cM
    Total of segments > 7 cM = 15.8 cM
    1 matching segments
    Estimated number of generations to MRCA = 4.9

    Any help would be helpful.

    Like

  29. ladarius1991 says:

    I did the GEDMatch one to one comparison with a cousin that I’m pretty sure is a 3rd cousin twice removed. However, the 4.8 generation estimation to our MRCA really threw a curve ball of whether we fall into the category of being 3rd cousins twice removed or 4th cousins. Same with another cousin who I considered a 3rd cousin twice removed and our MRCA estimation is 4.9 generations back.

    Me and My Cousin D.B.
    Largest segment = 17.5 cM
    Total of segments > 7 cM = 17.5 cM
    1 matching segments
    Estimated number of generations to MRCA = 4.8

    Me and My Cousin C.R.
    Largest segment = 15.8 cM
    Total of segments > 7 cM = 15.8 cM
    1 matching segments
    Estimated number of generations to MRCA = 4.9

    Any help would be nice.

    Like

    • gengenaus says:

      This is not at all unusual and it just goes to show that the further distant the relationship, the more unreliable the suggested Gedmatch generational difference becomes. Remember, this is just a guide – a suggestion from Gedmatch about how far back you might look to connect. As you can see from my own results above, at 4.4 I had a very wide range of actual relationships, including 3C2R. It doesn’t mean you need to look for other answers beyond what you have already ascertained of being 3C2R – you have the right answer 🙂

      Like

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