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How Many Ancestors Are In 20 Generations?

Have you ever wondered how many ancestors are in your family going back 20 generations? In this post, find out the answer, and much more about this topic.

How Many Ancestors Are In 20 Generations?

It’s hard to imagine how many ancestors we might have in our tree going back several generations because we typically only think about our parents and grandparents. That’s only six ancestors altogether!

If you were going to have a party and it would be possible to have all of your ancestors in 20 generations attend, how big of a venue would you need?

Would you believe it if I told you that almost as many people as live in the entire state of New Mexico. I don’t know about you, but I don’t have any experience hosting gatherings of that size.

How many total ancestors are in 20 generations?

The total number of ancestors in 20 generations of your tree is 2,097,150. In other words, you have more than two million spots in your family tree to fill up going back that many generations.

This number was calculated by adding up the number of ancestors for each generation one-by-one, and then adding all of numbers together.

For those of us that like to learn about who our ancestors were and add this information to our family trees, it means that if we were to actually able to learn who our ancestors were going back on all lines of every branch of our tree, we would have more than two million individual places in our family tree.

And that’s only for ancestors. This is not counting the collateral lines of our tree that are the siblings of our ancestors and their descendants.

For the average person, 20 generations of ancestors will take us back about 500 years. This takes us back solidly to the Middle Ages in most families.

How many ancestors are in each generation for 20 generations (table)

The table below shows you how many ancestors are in each generation 1-20. In the final column, you will see a running total, or the cumulative number of all ancestors.

Generation ## of ancestors in the generationCumulative # of ancestors
1 22
You are generation zero in this table, and your parents are generation one

For example, you will find that six generations back in our tree we have 64 great-great-great-great grandparents. However, we have 126 ancestors in all at six generations back because we add 2+4+8+16+32+64 to get 126 in all.

How far back in our family tree is 20 generations?

It’s a good thing that most genealogists can’t go back 500 years very many branches of their family. Two million spots in a tree would take quite a bit of time to research!

Of course, the exact number of years in a generation will vary from family to family. Regardless of the exact number of years per generation, we would still find that twenty generations takes us back between 400-600 years in almost all families.

Could you build a family tree back 20 generations?

I was checking out some of the oldest lines of my own family tree and I have one line of my tree that has been researched pretty thoroughly back 12 generations to my 10th great-grandmother Persis, born around 1626 in Massachusetts.

From there, the research is spottier, but I have some evidence to link me to an ancestor on that line born in England in the 1450s, and that is only 18 generations back. Records exist about this ancestor because he was the father of someone notable (notorious?).

Most experienced genealogists would rightly be skeptical about the claim I just made, since we all know that most people can’t build their family tree that far back. 500 years and two million ancestors offer a lot of unknowns!

How are so many ancestors possible?

If you are wondering how it is possible to have so many ancestors, you are asking the right questions. We essentially know that we need to fill more than two million individual spots on our family tree if we go back 20 generations because everyone has a mother and father.

It’s really as simple as that. However, when we think about how many ancestors we actually have, especially going back 400-600 in time in our family history, the answer tends to be less straight-forward.

If we were to examine every single ancestor in almost anyone’s family tree, we would eventually find somewhere – perhaps 10-15 generations ago – where the same person appears more than once. We can have the same person occupying more than one location in a family tree.

This is not weird at all. In fact, it’s super common and very normal.

It’s because, at the end of the day, we are all related to each other in some way. Some of us are very distantly related, and others of us are more closely related.

The same could be said for our ancestors. In communities where outsiders were a rarity, and travel was expensive and difficult, people chose partners who lived close-by. This often meant that partners might have been distant cousins, even if the couple didn’t know it.

This is a phenomenon called pedigree collapse. It has happened at some point in all family trees, we can be sure of it.

Regardless of how many ancestors we should have based off these estimated calculations, there is one thing that we can all feel sure about. No matter the exact number of ancestors, we have a lot of them going back twenty generations.


I hope this post has helped you understand more about the impressive number of people that are in our family tree as ancestors going back twenty generations. If you have any questions about something that you read in this post, please join in the discussion below.

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