The article “How Many Ancestors Do I Have?” helps you determine how many ancestors you have.

The formula is simple—the number doubles with every generation. You have 2 parents. Each of your parents has 2 parents, for a total of 4. They each have 2 parents for a total of 8, and so on.

The table below shows how the numbers add up. By the time you’ve gotten back to your 10th-great-grandparents, you could have around 8,000 ancestors!

If you want to use an actual formula, use 2ⁿ=X. Replace n with the number of generations back from you, and X will be the number of ancestors in that generation.

However, a possible wrinkle affects these calculations. Depending on the time and culture, cousins may have married cousins, making a branch on your tree “collapse,” so to speak. In other words, 2 of your ancestors in the same generation could have had the same grandparents, so their ancestral lines converge. The further you go back in time, the more a collapse is likely. Still, the formula gives you a pretty good approximation, especially for more recent generations.