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What is Unweighted Shared DNA on Ancestry?

Do you want to learn about the unweighted shared DNA data on Ancestry? In this post, find out the differences between weighted and unweighted shared DNA, how this information is calculated and how to use it in researching your connection to your DNA matches.

You will learn:

  • Where to find unweighted shared DNA on your DNA match list
  • Exactly what is unweighted shared DNA
  • What’s the difference between weighted and unweighted DNA
  • How to understand the weighted shared DNA details
What is Unweighted Shared DNA on Ancestry

The unweighted shared DNA feature was added to Ancestry in the fall of 2020. Prior to September, 2020, we could only see the total amount of shared DNA along with the total number of shared DNA segments.

It is very helpful to have access to the total amount of shared DNA, the size of the longest segment, and the total amount of unweighted shared DNA. However, we often have more questions as we get access to more information.

I hope that the information that you find in this article helps you understand this information and learn more from your match list.

Where to find unweighted shared DNA details on Ancestry

To find the unweighted shared DNA, you must first choose a DNA match to examine. Then, click on the blue link containing the total shared DNA and number of DNA segments that shows up after “Shared DNA”.

The image below indicates exactly where you should click to access the unweighted DNA information:

This image shows where to click on Ancestry DNA match to find the unweighted DNA information, as well as other shared DNA details.  It it a link right next to the words "Shared DNA" located on the DNA match profile
Click on the blue linked text where it says how much DNA you share with your match. In the image above, I would click where it says 368 cM across 14 segments

A window will appear that contains more details about the DNA that you share with your relative. You’ll see the total number of shared centimorgans, the number of DNA segments, the total number of unweighted shared DNA, and the size of the longest DNA segment:

These two DNA matches share 76 cMs of DNA across 4 segments, with unweighted shared DNA being 83 cMs, and a longest segment of 27 cMs
If you scroll down on this page, you will also see probability information which tells you the likelihood of you being related to your DNA match in a number of different ways

In the image above, you can see that I share 76 cMs of total DNA with my match. The longest segment of DNA is 27 cMs, and the amount of unweighted DNA is 83 cMs.

To find more about what all of this information means, keep reading. I’ll discuss it more in detail below.

What is unweighted DNA on Ancestry?

Unweighted shared DNA on Ancestry is the total number centimorgans shared between two DNA matches before Ancestry’s Timber algorithm. “Weighting” by the Timber algorithm assigns more weight to shared DNA segments that are likely due to an ancestor that could be identified with family tree research.

Timber identifies DNA segments that are shared between large numbers of Ancestry DNA customers who share common geographic origins. While these segments do indicate a common ancestry, the most recent common ancestor is not not likely to be within the genealogical time frame.

What is the difference between weighted and unweighted DNA?

Unweighted shared DNA is the total amount of DNA shared between two Ancestry DNA customers before the application of the Timber algorithm that assigns less weight to DNA segments that were unlikely to have been inherited by a recent ancestor.

Timber filters out entire DNA segments and weights DNA segments more likely to be from recent common ancestors in order to provide us with a DNA match list that is more useful for genealogy research.

Sometimes, you will find that the unweighted DNA is more than the total shared DNA. How is this possible?

The answer is due to the Timber algorithm that I discussed above. When Timber assigns a lower value to a DNA segment that is shared between thousands or tens of thousands of Ancestry DNA customers, it reports it as a smaller segment than it actually is.

We will only notice this phenomenon when we have matches with whom we only share one segment of DNA. This is because we can’t see detailed segment and chromosome data on Ancestry.

For example, in the image below you can see that the total shared DNA is 50 cMs across one segment (weighted). The unweighted DNA that I share with this match is 52 cMs, which also happens to be the same amount as the length of the longest segment (unweighted).

I share 50 cMs across 1 segment with this match.  Unweighted shared DNA is 52 cMs and the longest segment is 52, since we only share 1 segment
While I only share one DNA segment with this relative, it is fairly long

If your DNA match is a relatively close relative who shares more than 90 centimorgans with you, then you will find that the total shared DNA matches the unweighted DNA. This is because the algorithm that assigns more weight to DNA segments that are likely to be inherited from a recent ancestor (Timber) is not used on DNA matches who share more than 90 cMs.

An example of unweighted shared DNA.  In this case, since the matches are relatively close relatives sharing more than 90 cM, the Timber algorithm is not applied
There was Timber algorithm applied to this match due to the close relationship

The DNA match displayed above is a second cousin sharing 368 centimorgans. The unweighted shared DNA is the same as the total shared DNA because the Timber algorithm is not used for close DNA matches because most of the shared DNA segments are likely inherited from the recent common ancestors.

Which is more accurate: Weighted or unweighted shared DNA?

The weighted shared DNA, which is the amount that we see reported on the DNA match profile page, is the most accurate number to use when trying to determine how we are related to a DNA match.

Conclusion

I hope that this post helped you understand more about unweighted shared DNA, including what it is, and how to use the information to research your matches. If you have any questions about something that you read in this post, please feel free to join us in the discussion below.

Thanks for stopping by today!

Share the knowledge!

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Carlos

Monday 7th of November 2022

I have t Dna Matches on ancestry that are related to each other (Mother, Daughter) The mother and I share 3% shared DNA: 205 cM across 11 segments, while the daughter and I share, 29 cM across 5 segments Unweighted shared DNA: 72 cM Longest segment: 23 cM. Is it possible that the algorithm that assigns weight to DNA ot it wrong and iI actually share more weighted DNA than what is reported. The mother and I are half 1st cousins 1x removed.

Anna-Lee

Thursday 6th of October 2022

I am needing help understanding this unweighted thing

Jason Lee

Sunday 17th of April 2022

I haven't seen convincing evidence to support the idea that Timber is a net benefit. There's been no scientific peer review that I'm aware of.

Jess

Sunday 20th of March 2022

I just don't understand this at all. I have a 1rst cousin 1 time removed that is showing we only share 46 cM but the unweighted is 73 cM, on 4 segments.

Tim Riley

Sunday 20th of November 2022

@Jess,

I use the unweighted DNA # when using the shared cM Tool on DNApainter.com and it works out quite well.

In your case, I would take a closer look at that 73cM match. It is too low for a 1st cousin, once removed (1C1R). Some possibilities might be 1/2 1C1R, 1C2R, 2C, or 2C1R.

Tim R

Stacey

Tuesday 3rd of August 2021

I think this statement is confusing: "We will only notice this phenomenon when we have matches with whom we only share one segment of DNA." Can you go into more detail about this?

My match to a second cousin 1X removed: shared DNA 43 cM across 5 segments, longest segment 20 CM. Unweighted = 60 cM.

My shared segments are 5, not one.

I think what you are saying is in a certain scenario "something" will happen if you share only one segment. But, you are not saying that you will only see a different unweighted value if you only share one segment.

My situation is the same as the first person who posted a comment. There is a difference in shared versus unweighted AND they have 3 segments, not one:

"17 cM across 3 segments; Unweighted shared DNA: 33 cM

Stacey

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