Double Match Triangulator (DMT)

Double Match Triangulator is an autosomal DNA analysis tool.

DMT combines segment match data of two or more people to find all the double matches and all the triangulations between them. This gives you information that can help you determine your common ancestors and how you are related to your DNA relatives.

DMT can accept data from FamilyTreeDNA, 23andMe, MyHeritage DNA, or GEDmatch.

Download and Try Double Match Triangulator:

Latest Version:
2.1, 7 Mar 2018

DMT contains no adware, spyware, viruses or malicious software of any type.
The program has been code-signed for your protection.

DMT runs on Windows 7, 8 or 10.

The unlicensed version of DMT excludes details for chromosomes 2 to 23.

See the History page for what's new in each version.


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What DMT Does

DMT reads two or more segment match files that you can download from several DNA services. The process of looking for segments that overlap used to be a tedious one. DMT quickly and visually presents you with all the segments that overlap between two or more people and saves you the work of trying to discover the segments yourself. It produces Excel files with information and visual maps of the matches as well as an index of all the people you match to and how you match them.


  • A "Double Match" is where "Person A matches Person C" and "Person B matches Person C" on a segment. Only if "Person A also matches Person B" on the segment, then the segment is said to "Triangulate", otherwise the segment is a "Missing AB Match".
  • Double match segments that overlap form "Triangulation Groups". People in these groups could be sharing a common ancestor. If the double match also triangulates, then the segment of DNA may be from the common ancestor. Triangulation groups are your key to finding how other DNA testers are related to you.

The DMT main window looks like this:

DMT lets you enter the match file for Person A and the match file for Person B or a directory containing Person B match files to compare Person A with.

The DMT Map page looks like this:

Double Match Triangulator delimits triangulation groups helping you identify segments of Person A's DNA that may come from a particular ancestor.

I cannot possibly explain everything about matching segments and triangulation. To learn about this like I did, please read every post in Jim Bartlett's fantastic website.



This program requires Windows and has been tested back to Windows 7. It will produce formatted Excel files in .xlsx format that can be read by most spreadsheet programs.

Mac users: Sorry but there is only a Windows version. If you have Excel on your Mac, you can still read the Excel files that DMT produces. You can ask one of your DNA relatives to run the program and send you the Excel output files. Also, Peter Sjölund said on Facebook that DMT "runs like a charm on a Mac using Crossover or some other software that lets you run Windows applications."


Using the Program

I've included a fairly comprehensive help file with the program that you can access at this website via the Help link at the top. Please read it. From the program, press the Help button to open the help file locally. The last page of the help file is about interpreting results.

Downloading from Family Tree DNA

DMT was first designed to work with Family Tree DNA Chromosome Browser Results files. This file contains all the segment matches with every DNA related person. It can be very large, containing hundreds of thousands of lines and be 15 MB in size or larger.

Make sure you download the correct file. You do it from the Chromosome Browser page at Family Tree DNA by pressing the right-most link that says "Download All Matches to Excel (CSV Format)". The link you want to press is shown below in orange with the hand pointing to it.

Because the Chromosome Browser Results file is so large, it could take a few seconds to respond after you click the link, and it may take a couple of minutes to complete the download.

And don't forget: You need at least two files. Yourself and some other people whose kits you are administering. If you don't administer anyone else, you'll have to ask a DNA relative to download theirs and send it to you.

Downloading from 23andMe

23andMe also allows downloading of chromosome matches. Select: All Tools -> DNA Relatives and then go to the bottom of the page and click on "Download aggregate data" that is shown by the hand pointer below:

This will download a special file with a name like: nnnnnn_relatives_download.csv

Important note: 23andMe does not include the name of the tester in the file. The only indication who the tester is is from the nnnnnn in the filename. If the name in the filename does not match the reference to that person in the other person's match file, then it can't find the matches between them. DMT gives you a warning about this, and tells you to what you should do to change to change the filename.

Downloading from MyHeritage DNA

MyHeritage DNA now allows downloading of chromosome matches. From the DNA Matches screen, select the "Advanced options" dropdown and then click on "Export shared DNA segment info for all DNA Matches". This will download a special file with a name like: nnnnnn DNA Matches shared segments dddddd.csv

Downloading from GEDmatch

The GEDmatch site does not provide a download, but does produce a web-based report for you with the segment match information.

What you need to do is run the GEDMatch Tier 1 Utility -> Matching Segment Search. Once the results appear in your web browser, you select the entire page and copy it to your clipboard. Then, in Double Match Triangulator you can press the "Save GEDMatch" button, and this information will be saved in a file on your computer.

At GEDmatch, you will need a Tier 1 subscription to run the Matching Segment Search. GEDmatch allows you to subscribe to Tier 1 at $10 a month for a period as short as a month.

Downloading from AncestryDNA

AncestryDNA does not let you download your segment matches. The only way to get your segment match data from them is to upload your raw data into GEDmatch and to then download the segment match file from GEDmatch as described above. You'll only be able to get your segment matches to others who have uploaded their data into GEDmatch, but there are a large number of people who have.

Sample Files

If you don't have segment match files of your own to use, you can try this set of 5 sample files that is used for examples in the Help file. They are compressed in zip format.

Keep In Mind...

You can't mix data between Family Tree DNA, 23andMe, MyHeritage DNA and GEDmatch. DMT uses the person's name and/or kit number to identify the match and kit numbers always differ and names often differ between the three companies. Also, the companies use different algorithms, have different matching criteria and will have their own and thus different base addresses for what should be identical matches.

Small Segments: Triangulation does NOT mean that a match is Identical by Descent (IBD). It still could be a match by chance. I discussed this with Debbie Kennett and realized she is quite correct on this point. If Person A and B have an IBD shared segment, then Person C could match that shared segment by chance, and if so, Person C will appear to triangulate. However, triangulation is useful as it does reduce the likelihood of a chance match. Jim Bartlett is fairly confident that triangulation works down to 7 cM and maybe even 5 cM and my observations seem to confirm his.

But don't throw away the small triangulated segments under 5 cM: They may be by chance, but then again they may not. Multiple matches of related people over the same segments with matching crossover points could help to indicate which small segments may be real. Still, you should do everything you can with your larger matching segments first before you attack the smaller ones.

Also, don't throw the missing AB matches away. Although they cannot be IBD, they still may indicate a common ancestor, who might have passed his segment to Person A and Person C, and the ancestor's spouse might have passed her segment to Person B and Person C, which could explain why Person A and Person B don't match. Until the DMT program was made available, there hadn't been an easy way to identify missing AB matches, so no one so far has studied this and evaluated their usefulness. More research is needed to see how missing AB matches can be used. See my blog posts: Triangulation and Missing a-b Segments and Revisiting Missing A-B Matches.

The key to analysis is to try to build up your chromosome map. Try using DMT to first identify the matches that belong to each of your parents. Then subdivide those into their parents, and keep going back as far as you can. I'm hoping to work some of that logic into a future version of DMT to help you with this task.