Ancestry Only Shows Shared Matches of 20 cM and Greater – What That Means & Why It Matters

Recently, I’ve noticed an uptick in confused people who’ve taken Ancestry’s DNA test.

They are using shared matches, which is a great tool and exactly what they should be doing, but they become confused when no shared matches appear with some specific people.

This is especially perplexing when they know through information sharing or because they manage multiple DNA kits that those two people who both match them actually do share DNA and match each other, meaning they “should” appear on a shared match list. Or worse, yet, conflicting match information is displayed, with one person showing the shared match, but the other person reciprocally does not.

What gives?

That’s exactly what this article addresses. It’s not quite as simple as it sounds, but it’s certainly easier once you understand.

What Are Matches and Shared Matches?

Matches occur when two people match each other. From your perspective as a DNA tester, matches are people who have taken DNA tests and appear on your match list because you share some level of DNA equal to or greater than the match threshold of the vendor in question.

At Ancestry, that minimum matching threshold is 8 cM (centimorgans) of matching DNA.

Individual matches are always one-to-one. Your match list is a list of people who all match you.

So, you match person 1, and you match person 2, individually.

Your matches may or may not also match each other. If they do match each other in addition to matching you, that’s a shared match which is a hint as to a potential common ancestor between all three people.

Shared matches are a list of people who match you PLUS any one other match on your list. In other words, shared matches are three-way matches.

In the diagram above, you can see that you match Match 1 and you also match Match 2. In this case, Match 1 and Match 2 also match each other, so all three of you match each other, but not necessarily on the same segment. Therefore, you’re all three shared matches, as shown in the center of the three circles.

Viewing Shared Matches

To view a list of people who match you and Match 1, you would request shared matches with Match 1 by clicking on “View Match” or “Learn More” on your match list, then on “Shared Matches” on the next screen.

The resulting shared match list consist of people who match you AND Match 1, both. It’s easy to make assumptions about why you have shared matches, but don’t.

Shared Matches are Hints

A shared match CAN mean:

  • That all three people share a common ancestral line.
  • You share a common ancestor with Match 1 and Match 2, but Match 1 and 2 match each other because they share an entirely different ancestor.
  • You match Match 1 because you share DNA from Ancestor A and you match Match 2 because you share DNA from Ancestor B. Match 1 and 2 match each other either because they share one or both of those common ancestors.
  • Match 1 and Match 2 might match because Match 1 and Match 2 share an ancestor that isn’t related to you.
  • That one (or more) of the matches is identical by chance, meaning the DNA combined from two parents in a random way that just happens to match with someone else.

Shared matches are great hints to be sifted for relevance. The operative word here is hint.

What If We Don’t Have Shared Matches?

Conversely, NOT having a shared match doesn’t mean you don’t share a common ancestor.

Sorry about the triple negative. Let me say that another way, because this is important.

Even though you and someone else aren’t on a shared match list, you might still share DNA and you may share a common ancestor, whether you share their DNA or not.

Ancestry’s shared matches work differently than shared matches at other vendors. Before we discuss that, let’s talk about why shared matches are important.

Why Do Shared Matches Matter Anyway?

Matches and shared matches are how genealogists perform two critically important functions:

  • Verifying “known” ancestors. Sometimes paper trails aren’t accurate and certainly, neither are trees.
  • Identifying unknown ancestors. Looking for common families among shared DNA matches is a HUGE hint when tracking down those pesky unknown ancestors.

I wrote about shared matches, here, when Ancestry purged segments under 8 cM, but I think the message about the limitations of shared matches and how the process actually works deserves its own article, especially for new users. Shared matches and segment cM numbers can be quite confusing, but they don’t need to be.

I wrote an article titled DNA Beginnings: Matching at Ancestry and What It Means that includes lots of useful information.

Ok, now let’s look specifically at using shared matches and why sometimes shared matches just don’t seem to make sense.

Matches

By far, the majority of your matches at any vendor will be more distant matches. That’s because you have thousands of distant relatives, most of whom you don’t know (yet).

You’ll only have a few closer relatives.

At Ancestry, I have 102,000+ total matches, of which more than 97,000 are distant matches. Based on these numbers, keep in mind that about 95.74% of my matches are distant, meaning 20 cM or below, and yours probably are too. You’ll need that number later.

Note that 20 cM is Ancestry’s threshold between close matches and distant matches.

That’s about exactly where you’d expect, on average, to see a 20 cM match – generally at or further back than 4th cousins. 20 cM is roughly the 4th to 6th cousin level.

Of course, you won’t match most of your 5th cousins at all, yet you’ll match some with more than 20 cM. That’s just the roll of the genetic dice.

Closer ancestors (meaning closer matches) is also the area of genealogy where much of the lower-hanging fruit has been plucked.

In my case, the closest unknown ancestor in my tree occurs at the 6th generation level and I have 5 or 6 missing sixth-generation ancestors – all females with no surnames. Two have no names at all.

Click to enlarge any image

How Much DNA Do Cousins Share?

One of my priorities as a genealogist is to identify those unknown people, which is why matches, and shared matching at that level are critical for me.

Ancestry tells me that this 20 cM match is likely my 4th-6th cousin.

At DNAPainter, in the Shared cM Tool, you can enter the total cM number of a match, which is the total amount of DNA that you share after Ancestry’s Timber algorithm has been applied. The range of relationship probabilities for 20 cM is shown below.

For a total match of 20 cM with another individual, several relationships ranging between half 3C2R/3C3R and 8th cousins are the most probable relationships at 58%.

For the record, this is total cM, which does not necessarily mean one segment. Ancestry reports the number of segments, but Ancestry does not show you the segment locations, nor do they have a chromosome browser. Without a chromosome browser, you have no way of determining whether or not you match with shared matches on the same segment(s). In other words, there is no triangulation at Ancestry, meaning confirmation of a specific shared DNA segment descended from a common ancestor. You can find triangulation resources, here.

Close Matches

The best way to figure out how you are related to closer matches (assuming you don’t already know them and Ancestry has not found a common ancestor) is using shared matches. Hopefully, you will share matches with people you do know or with whom you’ve already identified your common ancestor.

One of my relatively close DNA matches at Ancestry is Lonnie. I don’t know Lonnie, but it looks like I should because he’s probably a 1st or 2nd cousin. We share 357 cM of DNA over 20 segments.

I thought I knew all of my 1st and 2nd cousins. Let’s see if I can figure out how I’m related to Lonnie.

By clicking on Lonnie’s name on my match list, then on Shared Matches, I can determine that Lonnie and I connect through my Estes and Vannoy lines based on who we both match, which means that our common ancestor is either my paternal grandfather or my great-grandparents, Lazarus Estes and Elizabeth Vannoy.

You can see the notes I’ve made about these matches I share with Lonnie.

Viewing Lonnie’s unlinked tree verifies the ancestral line that shared matches suggest. An unlinked tree means that Lonnie has not linked his DNA test to himself in his tree. Since Ancestry doesn’t know who he is in the tree, they can’t find a common ancestor for me and Lonnie. However, I can by viewing his tree.

Our common ancestor is Lazarus Estes and his wife, Elizabeth Vannoy. Therefore, Lonnie is my 2nd cousin.

That wasn’t difficult, in part because I had already worked on the genealogy of our common matches and Lonnie had a small unlinked tree where I could confirm our common ancestor.

Now let’s move to more distant, not-so-easy matches.

Distant Matches

I’ve spent a lot of time over the years identifying common ancestors with my matches.

When I make that connection, whether or not Ancestry has been able to identify our common ancestor, I make notes about common ancestors and anything else that seems relevant. Notes very conveniently show on my match list so I don’t need to open each match to see how we are related.

Ancestry does identify potential common ancestors using ThruLines. Note the word potential. Ancestry compares the trees of you and your matches searching for common ancestors and suggests connections. It’s up to you to verify. ThruLines are hints, not gospel. Additionally, you may have multiple ancestral links to your matches. Ancestry can only work with the fact that you have a DNA match with someone AND the user-provided trees of your matches.

Ancestry’s ThruLines only reach back a maximum of 7 generations to suggest common ancestors. At 7 generations distance, you’d be a 5th cousin to a descendant who is also 7 generations downstream from that ancestor.

The information from DNAPainter, who utilizes the Shared CM Project compiled data shows that the most likely amount of shared DNA for 5th cousins, is, you’ve guessed it – 20 cM.

Jacob Dobkins is my 7th generation ancestor. I have ThruLines for him and his wife, but not for their parents who are one generation too distant for ThruLines. I’d LOVE to see Ancestry extend ThruLines another 2 or 3 generations.

ThruLines matches me with people who descend from Jacob through his other children. Other children are important because the only ancestors you share with those people are (presumably) that ancestral couple.

Matches with Jacob’s descendants range from 8 cM (the smallest amount Ancestry reports) to 32 cM.

Here’s an example.

Ancestry displays some shared matches with all of your matches, regardless of the size of your match to that person. However, Ancestry ONLY shows shared matches to a third person if you share more than 20 cM of DNA with that third person.

For example, I match KO with 8 cM of DNA. Ancestry shows my shared matches with KO, below.

I only have 3 shared matches with KO. I only match KO at 8 cM, but I match our shared matches at 39, 31 and 21 cM, respectively.

Ancestry does NOT show shared matches below 20 cM, so it’s unknown how many additional shared matches KO and I actually have if shared matches less than 20 cM were displayed.

Perspective is Critical

Whether you see a shared match or not is sometimes a matter of perspective, meaning which of two people you request shared matches with.

In this case, I requested shared matches with KO. I only share 8 cM of DNA with KO, but that doesn’t matter. The amount of DNA you share with the person you’re requesting shared matches with is irrelevant.

Ancestry’s Shared Matches with KO include Ker

I will see shared matches with KO to anyone we mutually share as matches above 20 cM, including Ker.

If I request shared matches with Ker, with whom I share 39 cM of DNA, I will see all of our mutual matches at 20 cM (or greater) of DNA. However, that does NOT include KO because I only share 8 cM of DNA with KO.

This restriction applies regardless of how much DNA KO and Ker share, which is an unknown to me of course.

Ancestry’s Shared Matches with Ker does NOT include KO

Nothing has changed between these matches, yet KO does not appear on my shared matches list with Ker when I request shared matches with Ker.

I still share 8 cM with KO and 39 cM with Ker. KO and Ker still both match each other. The only difference is that Ker shows up on my shared match list with KO because I share more than 20 cM with Ker. However, when I request a match list with Ker, KO does NOT appear because I only share 8 cM with KO.

This is the source of the confusion and often, why people disagree about shared matches. It’s kind of a “now you see it, now you don’t” situation.

If a person shows as a shared match depends on:

  1. Whether the third person actually does share DNA with the tester and the person they’ve asked for shared matches with
  2. Whether the third person shares 20 cM DNA or more with the tester, the person requesting the shared match list with one of their matches

Whether someone appears on a shared match list can literally be a matter of perspective unless the match and the shared matches all match the tester at 20 cM or larger.

Another Example

Let’s look at a larger match to a descendant of the same ancestor.

I share exactly 20 cM with Joyce, my 5C1R.

Viewing my shared matches with Joyce, I match 50 other people that she matches as well.

I only share 25 cM of DNA with the smallest match with Joyce. Apparently, there are no matches with Joyce with whom I share between 20 and 25 cM of DNA.

Bottom Line

Here’s the bottom line.

Ancestry NEVER shows any shared matches below 20 cM from the perspective of the tester, meaning people who match you and someone else, both.

If you recall our earlier math, that means that approximately 95.74% of my shared matches aren’t shown.

This puts shared matches in a different perspective because now I realize just how many matches I’m not seeing.

Why is This Confusing?

If you aren’t aware of this shared match limitation, and that a majority of your shared matches are actually below 20 cM, you may interpret shared match results to mean you actually DON’T share specific matches with that other person. That isn’t necessarily true, as we saw above with KO and Ker.

Furthermore, let’s say you manage your DNA kit plus 3 more, A, B and C. Because you manage all 4 kits, that means you can see the results for all 4 people.

  • A – 10 cM
  • B – 20 cM
  • C – 40 cM

From the perspective of YOUR kit, you will see some shared matches FOR all of those matches.

What you won’t see is shared matches if you don’t match the shared match (third person) at 20 cM or greater.

Always remember, shared match information at Ancestry is ALWAYS from the perspective of your DNA kit combined with the person with whom you request the match.

I’ve put this information in a grid because that’s how I make sense of things like this.

Here are your matches. When you click on shared matches with person A who you match at 10 cM, you’ll see both person B and person C as shared matches since you match both of those people at 20 cM or larger. You WILL see 20 cM shared matches, but you will not see 19 cM shared matches.

When you request shared matches for A, you will see both B and C.

When you request shared matches with kits B and C, you will not see A because you only match them at 10 cM.

However, from the perspective of DNA kits A, B and C, shared matches look different.

Let’s look at shared matches from the perspective of Kits A, B and C.

Kit A matches you, Kit B and C, but can only see Kit B as a shared match because matches with you and Kit C are under 20 cM.

Kit B doesn’t match C at all, so they clearly won’t have shared matches. However, they do match you and Kit A, both at 20 cM and over, so Kit B will see you as a shared match with Kit A, and Kit A as a shared match with you.

Kit C doesn’t match Kit B, so no shared matches with that person at all. Kit C does match you and Kit A. However, when Kit C clicks on shared matches for you, Kit A doesn’t show up because they only match Kit A on 9 cM. When Kit C clicks on Kit A for shared matches, you ARE listed as a shared match because you share 40 cM of DNA with Kit C.

There’s no way to discern whether two of your matches match each other unless they show as a match in the shared match tool. You can’t tell if their absence on the shared match list means they actually don’t match, or their shared match absence is because they match you at less than 20 cM.

Whew, that was a mouthful.

You may need to refer back to this from time to time if you’re confused by your shared matches at Ancestry.

If you need to remember rules, remember this.

  1. You can obtain shared matches with yourself plus any match, regardless of how much or how little DNA you share with that one match. Prove this to yourself by finding a match under 20 cM, like my 8 cM match, and viewing your shared matches.
  2. No one will show on a shared match list with another person unless they match you at 20 cM or greater. Prove this to yourself by viewing the smallest shared match with anyone.

Strategy

The takeaway of this is if you have a larger (20 cM or over) and smaller match (under 20 cM), always request shared matches from the perspective of the smaller match because the smaller match won’t show up as a shared match on any shared match list.

The only way you can see shared matches that includes people under 20 cM is to request to view shared matches with individual people who match you below 20 cM. 

In my case, I will never see KO on any shared match list because I only match KO at 8 cM. However, I can request my shared matches with KO in which case I’ll see all 20 cM or greater shared matches with KO.

Alternatives

Every vendor provides a shared match feature, and each functions differently.

In the chart below, I’ve provided basic shared match information for each vendor.

If you’re interested in uploading your DNA file from Ancestry or another vendor, I’ve provided upload/download step-by-step instructions for each vendor, here.

_____________________________________________________________

Follow DNAexplain on Facebook, here or follow me on Twitter, here.

Share the Love!

You’re always welcome to forward articles or links to friends and share on social media.

If you haven’t already subscribed (it’s free,) you can receive an email whenever I publish by clicking the “follow” button on the main blog page, here.

You Can Help Keep This Blog Free

I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

DNA Purchases and Free Uploads

Genealogy Products and Services

My Book

Genealogy Books

Genealogy Research

16 thoughts on “Ancestry Only Shows Shared Matches of 20 cM and Greater – What That Means & Why It Matters

  1. I look at the shared matches of each new match regardless of cm amount. If there is at least 1 shared match, I enter basic info about that match on an Excel spreadsheet including the top shared match. That way as I eventually identify shared matches, I can search the spreadsheet and find the under 20cm people that also match them and hopefully this will provide more information about the connection.

    One thing that I added to the spreadsheet is the “managed by” name. I discovered that you can’t search for usernames that are initials. But you can search for the “managed by” name.

  2. Thanks for sharing Roberta. I’ve been trying to continuously explain the triple concept those in my groups. About the inside and detail of the chromosome browser I find many are misled on who is a match, where multiple assumptions are being made. Thanks again.

  3. Great article – thank you for the thorough explanations! I always cringe a bit when I see Ancestry’s threshold of 20 cM to separate “Close” and “Distant” matches. As you point out – and as is seen on the “Shared cM project” – after 3rd cousins, the match can be 0. I have a verified-with-certainty 3rd cousin with whom I match at only 7 cM (saved from The Purge!) – and this was an absolutely critical find for me in breaking down a brick wall. I understand Ancestry is using average shared cM, but when looking at any individual match, a 3rd cousin (that I would call “close”) can be a 7 cM match (or even, not a match!) In fact, I have a group of matches between 20 and 30 cM from various regions that have one ancestor in common that links back to 7th great-grandparents of mine – making us 8th cousins. So, I have a group of 8th cousins at 20-30 cM (“Close” per Ancestry) and a 3rd cousin at 7 cM (“Distant” per Ancestry) I can see how this confuses many people!

    I must also state my wish that Ancestry lower the shared match threshold down to 15 cM. I have one line of Irish ancestors from my 2nd great-grandmother with whom my highest match is 16 cM (after timber…) Thus, even though I have traced more than 1000 of my DNA matches to common ancestors – I only have a few identified in this one line and I don’t see any shared matches for them (I do have lots of “mystery” groups…) I have politely asked these users to share what they see (from their perspective of shared matches with me) but no response. Thus, I am stuck. If only ancestry would lower it – even if only temporarily!

  4. Great explanation! I wish I had known how to use shared matches when they first came out. With the help of people like you, I have learned how useful they can be. Also, I finally have a use for Venn diagrams!!!😁

  5. Hi Roberta,
    I don’t want to sound pedantic, but in your example with Joyce, the image shows her as being 5th cousin 1x removed, whereas you refer to her as 6C1R.

  6. I didn’t notice whether you addressed this — if I just missed it, I apologize — but it’s also important to understand that Ancestry bases this 20 cM requirement on the Timber-adjusted amount. You may often see matches who have *unweighted* sharing of greater than 20 cM. They still won’t appear as a shared match in any other match’s shared match list unless the *Timber* amount is at least 20 cM.

    Also, I’ve seen instances in which both my daughter and I match someone and the Timber-adjusted sharing is actually less for me than for her. This makes no sense in real life, but Timber-wise it may mean that Timber regarded some of the shared cM as “excess” for me but not for her. Of course, the reverse can also be true, but in real life she might share less with a mutual match than I do, simply because she didn’t inherit all of the DNA I share with that match.

    On a slightly different topic, but one I hope you might address at some point (if you haven’t already), Ancestry explains its exemption of matches with total sharing of 90 cM or more from Timber as being because such matches are likely to be too recent for “excess matching” to really be a factor. However, for some reason they did not elect to exempt matching in which a single segment is large enough that it probably cannot be explained simply as a result of excess matching.

    Also, they’re very literal about that 90 cM threshold. I have one match that Ancestry shows as having unweighted sharing of 90 cM, yet Timber adjusts total sharing with this person down to 78 cM. The only explanation I can find is that the actual sharing is probably something like 89.5 to 89.9 cM and simply shown as 90 cM due to rounding. Since it isn’t literally at least 90 cM, it’s fair game for Timber.

    This person actually is a 3rd cousin, so the adjustment is pretty meaningless anyway. Even at 78 cM, Ancestry estimates about an 82% chance that this match is *at least* a 3rd cousin.

    • They do if you link your known matches to your tree. Bucketed matches are the result of triangulation in the least one segment. Using the matrix tool you can see if your matches also match each other. I wrote an article about triangulation at FamilyTreeDNA and how to do it.

  7. I was thinking about a work around to the 20cm limit. If you send a message to dna matches and asking if they will be willing to go to sharing preferences and share. Then you can create match lists for yourself and any kits you manage and any dna matches that will share. Then use excel to compare dna match lists. You could go down to 8cm if you wished.

  8. I dont much like the Ancestry approach to DNA testing. It’s OK for confirming a tree but hopeless for resolving gaps or NPE. Their take it or leave it approach to DNA matching is annoying and pasting on a new user interface once a year with no new DNA tools seems cynical. Gedmatch has the best DNA tools but Europeans dont use it. MyHeritage has good DNA tools but their search is poor and they do seem to be European centric. At least you can export FTDNA, MyHeritage and Geneanet shared data to DNA painter.

    Its a huge problem to get older people to put data on the internet, most of my new matches now are 20-30 year olds. Perhaps dont buy a tombstone buy a DNA test. It will last longer as a marker for your existence and will be more useful to your ancestors. With each generation we’re losing on average half the DNA. With lower quality and higher numbers of matches we need more granular and selective tools.

    • MyHeritage has a great data base for Polynesian. My 2-year old ggranddaughter has 8,600 matches there. Her grandmother is Hawaiian and my ggran has mostly New Zealand matches, and a focus on the indigenous Maori tribe.

  9. Roberta, thank you for posting this. I have always used the Shared Matches feature at Ancesry but not to its fullest. Today, I did a Shared Match with 4 others on one of my Johnson/Johnston lines. We all matched each other, except one, who I threw out. Yes, I know this is a HINT for a CA, and not necessarily a true TG, but it advanced the ball and in my mind, it gave some credibility to a line that I could not prove with records, a line that has haunted me for more than a decade. In addition, it gives weight to the high % of Scottish heritage I get, especially at Ancestry. THANK YOU!

Leave a Reply