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What is a NPE?

Have you heard or read the acronym “NPE”?  Do you want to know what is a NPE and how common it is to see them in a family tree? 

In this post, I will answer all of these questions about NPEs, also known as non-paternity events, and more!

What is a NPE_

I discovered an potential NPE in my own family tree, which is what got me thinking about this topic. It turns out that one of my grandfather’s aunts, the older sister of his mother who he loved very much, was not the child of the person who was in my family tree listed as her father.

We discovered this particular NPE through DNA testing, since my father didn’t share enough DNA with his second cousin for it to be a “full” relationship.

What is an NPE?

NPE stands for a “non-paternity event”.  Non-paternity event means that the person who is assumed to be the father, usually the husband or partner of the mother, is not the biological father. 

The term NPE is not usually used in relation to adoption or step-parent situations. In cases such as these, the key individuals involved, most importantly those raising the child, generally know that the step parent or adoptive parent is not the biological parent.

Non-paternity events (NPEs) are also sometimes called mis-attributed paternity, not parent expected, or paternal discrepancy.  No matter which words you choose to describe the situation, it means one thing: paternity has been incorrectly assigned to the wrong male.

Sometimes, a person who was adopted might not be aware that they were adopted, and this person or their descendants might use the term “NPE” to describe the situation when they realize that their DNA results don’t show what they expected to see. 

The NPE that I have mentioned towards the beginning of this post from my family tree occurred very long ago. My grandfather’s favorite aunt was born in 1898, after all, and so it is ancient family history.

Everyone involved has long since passed away, and so I can’t say for sure whether it was a secret to everyone, or whether it was common knowledge that didn’t get passed down to future generations. My great-great grandmother was very pregnant when she married my great-great grandfather, and so I believe that he likely knew that someone else was the father.

Update: I have since been in touch with a granddaughter of this relative, and she is aware of the identity of her grandmother’s father. This means that her grandmother must have known, but we still are not sure if the rest of her siblings were aware.

How are most NPEs discovered?

Many people discover that there was a non paternity event in their family tree through DNA testing and genetic genealogy.

It’s important to note that DNA matches are the only aspect of autosomal DNA test results that can provide evidence of or dispute a theory of a NPE. Ethnicity estimates cannot be used as evidence to prove or dispute paternity.

In addition, we should also acknowledge that informal adoptions occurred frequently in the past, and sometimes the immediate or extended family was not aware of the adoption.  Since no one discussed the adoption, and the adopted child was raised as a biological child, descendants of this adopted child would not be aware of their true biological lineage.

With the advent of modern DNA testing, evidence of these adoptions comes to light.  So, sometimes a perceived “NPE” was not the result of any sort of dishonesty or deception, we just don’t always have all of the information.

How common are non-paternity events?

People are often surprised to learn about how common it is for a father to unknowingly raise a child, or assign his paternity to a child, that is not his in a biological sense.  It’s impossible to know exactly how many children are born to NPE situations, but lots of studies have been performed to try to figure out an average rate.

How do researchers figure out whether an NPE has occurred?  For modern populations (i.e. you and me), researchers are able to do studies of sample populations and actually perform paternity tests across the families in order to determine paternity (or non-paternity).

Other researchers focus on male lines of family trees, since men generally carry their expected father’s surnames, and use Y DNA testing to verify their hapologroup and Y DNA matches. 

Still others, experts in genetic genealogy, are able to perform studies using autosomal DNA (the kind of test that Ancestry DNA and 23 and Me perform) to determine whether or not the known family tree matches the DNA results.

For example, we have a lot of data that shows us an expected range of shared DNA (measured in centimorgans) between relatives of a particular relationship type. When the shared DNA amount doesn’t match up, we start to think about a possible NPE having occurred.

But, let’s get back to what you really want to know.  How common is this, really? 

Some of us prefer to believe that it has never, ever occurred in our family, while the more cynical among us might think that a NPE in genealogy is more common than correctly attributed paternity. 

In reality, NPEs have likely occurred in all of our families – and maybe more commonly than we might think, but not so much to make genealogy a hopeless endeavor.

Below are some interesting conclusions that can be drawn from several studies:

Less than 5% of births are NPEs, on average

The average rate of NPEs is less than 10%, and likely no higher than an average of 4%.  In other words, as many as 1 in 10 births might be incorrectly attributed to the wrong father, but it’s most likely that only about 1 in 25 births fall into this circumstance.

NPEs rates vary in across cultures

The actual rate of NPE can vary across time, culture, and geography, which means that there might be a slightly higher percentage of NPEs in some places (and not always the places that you would expect) and lower in others.

The father’s confidence matters

When there is “high paternal confidence” (meaning that the father feels very confident that he is the biological father of his child), there is a much lower percentage of NPEs than average – about 2%, or less than 1 birth out of 50 – pretty low odds!

When there is “low paternal confidence” (meaning that the father feels like there is a good chance that he is not the biological father of the child), the NPE rate can be as high as 30%.  This makes sense, however, since a lot of people who do paternity testing do it because they know that there might be a chance that there is a NPE, or they are unsure.  

We can assume that most of the time when a father assigns his last name to a child, especially within a marriage, that he assumes that the child is biologically his and has “high paternal confidence”.

You may or may not have an NPE in your family tree

People who are really into statistics might be tempted to extrapolate these numbers to help make general conclusions about how accurate the average family tree might be. In the case of non-paternity event statistics, it could lead us to assume that there are many births in our family tree that are attributed to the wrong male ancestor.

The assumption that all of our known ancestors are truly our ancestors has an important effect in genealogy. After all, we research our family tree to learn about our ancestors, and it is quite a shock to think that we may not be descended from some of the people that we spend so much time learning about.

Except in a tree where there is pedigree collapse, everyone has 64 individual great-great-great-great grandparents. If we assume that 4-10% of those ancestors are the result of mis-attributed paternity, or a non-paternity event, then that means that we have between 3-6 ancestors in our tree in those spots that don’t belong there.

Is this the case in every family? In reality, it’s impossible to say based only on the very general average rates of NPEs that I mentioned above how likely it is that they have occurred in significant numbers in your family tree.

The basic takeaway for a genealogist, or a genetic genealogist, would be to keep in mind that NPEs do happen and have occurred, and to make sure that DNA evidence backs up family tree research. There are some good techniques that can be used using data from our DNA results, such as the analysis of DNA matches and chromosome mapping using tools like DNA Painter.

Note:  DNA testing companies offer ethnicity estimates along with DNA matches.  Ethnicity estimates cannot and should not be used as evidence of a non-paternity event, nor should they be used to determine paternity.  DNA matches, on the other hand, can be quite useful for this purpose.


I hope that this post helped you understand what a NPE is, and how common it might be – or might not be.  I’d love to hear your thoughts on this topic, especially if you have any questions or would like to share your own experience discovering a NPE in your own family tree.

Thanks for stopping by today!

Pinterest image title:  What is a NPE, as well as a graphic of surprised cartoon eyes

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Naomi Fron

Friday 27th of October 2023

I happen to be a NPE. I was surprised when I took my DNA test in 2017 to find that there were DNA matches that I had no idea who they were. I contacted several of them and one replied. We corresponded frequently and with some evidence that we both had, came to the conclusion that her birth father was also my birth father! I had found a half-sister who accepted me. She had two other sisters who were not as welcoming, but that is OK. With military records, we were able to determine that our father and my mother were at the same place at the same 6 week period which happened to coincide with my conception period. We have become fast friend and have met and communicate constantly. I recently found out that I believe my maternal grandfather is also a NPE due to over 400 DNA matches that I was not able to make a connection with until I put in another man as my grandfathers birth father, and voila, they all fell into place. I cannot prove it with documentation, but I don't see any other way that we all match. I belong to a private group on FaceBook for NPEs and we now have I believe over 8,000 members. I wasn't raised with my BCF and was adopted by my mother's 2nd husband so I haven't had many of the traumatic and devastating issues that many of them have. Anyway, thank you for writing this, it is a much ignored area that many of us have to deal with.


Thursday 1st of June 2023

The bad news - you wish you didn't know. The good news - it's hard to imagine it being a thing much longer into the future.


Thursday 23rd of February 2023

My mother, Jane Fink Storm was raised in a small-town area in the hills of Pennsylvania. She was born in 1927 in a family of eight kids. Back in the early 1940’s her group of girlfriends were Debbie, Little Lori, and mom. Her brother Byrl was Debbie’s boyfriend/love. Little Lori was in love with Ron.

It was 1942 and my Uncle Byrl had decided to enter the military. Debbie was devastated. She wanted to get married but Byrl was afraid of leaving her a widow and refused. I know all of this because Mom eloped on the train almost 3000 miles away and was so homesick that she told me all the stories of her and her friends’ lives.

Debbie was upset with Byrl going in the military. She suddenly married Bill and had five kids. In 1944 Little Lori married Ron Newsome. They had a son, but the marriage was not strong. They divorced. Byrl came home after the war and married Little Lori. He adopted Lori’s son, Ron and then three more children were born.

But now comes 2020 and DNA! I discover s new first cousin! Keith does not see how this is possible! He has a last name that I recognize slightly in the back of my mind but when I hear his mother is Debbie’s name. It had to be Byrl and Debbie’s love. Keith was my Uncle Byrl’s son. He was born in 1948. Since Keith would not believe it was possible and I really did not want to be the one to tell him! I decided to do something logical. I called my cousin, Mick and explaining that I was doing our Fink family genealogy and asked If he would do a DNA kit at my expense for the family. Mick was my Uncle Byrl’s youngest child. Mick agreed to do a DNA kit for me but said he wanted to know nothing about the results or the genealogy. I agreed I would tell him nothing. Would you believe Mick was no DNA match to me nor my Fink family?

Now to tell you why I cannot let this out! My uncle died in 1961 at 35 and his wife, Little Lori died just three and a half years later. Mick was just seven when his Dad died and 10 ½ when his Mother died.

I two N.P.E.’s! I never should have done my cousin’s DNA. I want folks to know DO NOT TAKE IT UPON YOURSELVES TO DO ANOTHER PERSON’S DNA. This is not your business!

All names have been changed to protect the families.

La Ronda

Sunday 30th of January 2022

I am an NPE. Both my bio father and my BCF have passed. I learned that my BCF knew I was not his, and my BF never knew of me. I have been blessed to have been well excepted into my new family. I now have 4 sisters and 2 brothers, before I had only one sibling. Yes there were secrets it seems everyone knew of, but me until I was 53. I know there are NPE’s on my maternal side also. Could you direct me to a simplified way of discovering them. I have worked on this for 3 years and have not found a way to understand what I am seeing. Thank You for any help you may have.


Sunday 4th of September 2022

@Lori MacGregor, I am an NPE who descends from a heavily endogamous family. My first search angel quit because she was not an endogamy expert. I strongly recommend that if someone comes from an endogamous family to use a search angel who knows about endogamy. Using a search angel who is not familiar with endogamy will prolong the search.

Lori MacGregor

Tuesday 12th of April 2022

@La Ronda, If you are on Facebook, please look for DNA groups like 'DNA Detectives'. In these groups are wonderful souls called 'Search Angels' and they assist searchers (FOR FREE) to find family. If you are not on Facebook, google 'Search Angel' and you may find assistance that way. I am afraid there is no easy way to pick apart DNA results from an NPE over 100 years ago (from experience, and I teach Genetic Genealogy), although I would recommend looking at the "Finding Bio Family" playlist on the channel 'DNA Family Trees' on YouTube. Larry is an excellent teacher, and he explains using the Leeds method of clustering your matches with identifying colours, which works very well. Hope this helps, now back to work researching NPE percentages to teach to my students tomorrow!


Sunday 30th of January 2022

Was it possible in 1929 New York to lie about who the mother was on a birth certificate? Grandmother's name instead of birth mother to hide a pregnancy?

Lori MacGregor

Tuesday 12th of April 2022

@S, If baby was born at home, with no healthcare attendant, and the witness giving the birth details to the registrar (after the fact) was someone willing to cover up the situation, then yes. Especially if the family could use lack of education or English to hide behind. No registrar was going to check who was bleeding to certify the birth mother.

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