Double Match Triangulator (DMT)

Double Match Triangulator is an autosomal DNA analysis tool.

DMT combines segment match data of two or more people to provide you with Double Match and Triangulation information that will help you find common ancestors and help you determine how your DNA matches are related.

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

Download and Try Double Match Triangulator:

Latest Version:
1.5, 22 Mar 2017

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.
If you have Office 2007 or later, DMT produces an Excel file.
Otherwise it creates a comma delimited (.csv) file.

The unlicensed version of DMT hides most of the Person c names.


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What DMT Does

DMT is an autosomal tool that assists you by finding every segment from every matching person that Double Matches and/or Triangulates with two specific people. It produces an Excel file that contains a Map page that displays every matching segment and a People page listing all the people who match.


  • 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 a-b" Double Match.
  • Double Match segments that overlap form "Double Match Groups". If any segments in the Double Match Group triangulate, then the group becomes a "Triangulation Group". People in these groups could be getting their DNA from a common ancestor. Triangulation Groups and Double Match Groups are your key to finding how other DNA testers are related to you.

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

The DMT Map page looks like this:

Double Match Triangulator delimits Double Match Groups (DMG) helping you identify segments of Person a's DNA that may come from a particular ancestor.



This program requires Windows and has been tested back to Windows 7. If you have at least version 2007 of Excel installed on your computer, it will produce formatted Excel files in .xlsx format. If you don't have at least version 2007 of Excel installed, it will produce Comma Delimited files (csv files) which contain the same data and can be loaded into any spreadsheet program, but you won't get the nice formatting. In that case, you can format it yourself (e.g. cells with X = green, a = pink, b = blue, etc.)

Mac Users: Currently there is only a Windows Version. If you have Excel on your Mac, you can still read in the files DMT produces. So ask one of your DNA relatives if they would run the program and send you the Excel output file. 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 is also available at this website from the Help tab. Please read it. Press the Help button in the program to open the help file. The last page of the Help File is about interpreting results.

Downloading from FamilyTreeDNA

DMT was first designed to work with FamilyTreeDNA Chromosome Browser Results files. This file is a hidden gem at FamilyTreeDNA that not too many people have discovered. It contains all the segment matches with every person that is matched. This file 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 FamilyTreeDNA 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 may take up to a couple of minutes after you click the download link before the FamilyTreeDNA site does anything at all, but then it will start to download the file. Wait until it says 100% before you try to use it. So be patient! Give it time to complete the download. Several minutes. Don't click the link a hundred times either.

Also, FamilyTreeDNA is a very busy site. Sometimes the download fails. If it creates a file whose name ends with _aspx, then it failed. Press cancel and try again or wait until later when their servers are less busy. If the download succeeded, the file downloaded will have have a name that looks like this: nnnnnn_Chromosome_Browser_Results_yyyymmdd.csv

And don't forget: You need two files. Yourself and someone else 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 GEDmatch

The GEDmatch site does not provide a segment match download, but with a small bit of work, you can screen capture match information from GEDmatch and use it in DMT. See: Getting DMT to work with GEDmatch segment matches. Match files from GEDmatch cannot be used with match files from FamilyTreeDNA because the identifying people names are different. A similar process will also work for 23andMe match downloads. AncestryDNA does not provide match downloads.

Downloading from 23andMe

23andMe does allow downloading of chromosome matches. The next version of DMT will include capability to read these files directly. Until then, if you reformat them like a FamilyTreeDNA CBR file, then DMT will read them.

Downloading from AncestryDNA or MyHeritage DNA

AncestryDNA does not let you download your segment matches. MyHeritage DNA is a new service that does not yet offer downloads. The only way to get them is to load them into GEDmatch.

Sample Files

If you don't have Chromosome Browser Results files of your own to use, you can try this set of 5 sample files used in the Help file. They are compressed in zip format.

Keep In Mind...

You can't mix data between FamilyTreeDNA, GEDmatch and 23andMe. DMT uses the person's name to identify the match because that's all FamilyTreeDNA provides in their CBR file. The person's name is often different in GEDmatch and 23andMe, so the people will usually not match each other across companies. Also, the companies use different algorithms, have different matching criteria and will have their own and thus diffent base addresses for what should be identical matches.

Small Segments: Triangulation does NOT guarantee 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 are IBD, then if person c matches a by chance, then person c will also match person b by chance. However, Triangulation is useful as it does reduce the likelihood of a chance match. Jim Bartlett is fairly confident that Triangulation works down to 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. Finding multiple matches at certain crossover points will add weight to indicate which small segments may be real.

Also, don't throw the missing a-b Double Matches away. They can be very valuable and may come from a common ancestor who passed his segment to Person a and Person c, and the ancestor's spouse who 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 a-b Double Matches, so no one so far has studied this and evaluated their usefulness. More research is needed to see how missing a-b matches can be used. See my blog post: Triangulation and Missing a-b Segments.

The key to analysis may prove to be looking at the crossover points. If multiple people have identical crossover points, it should reduce the likelihood of it being a by chance segment. Those crossover addresses given by FamilyTreeDNA seem to be quite accurate and seem to be consistent in different people's match files. And here as well, more research is needed to explore these possibilities.