Daily AncestorGeneration calculator
Each generation back adds one "great": your great-great-grandparents are 4 generations up, you have 16 of them, and a generation in family trees averages roughly 30 years.
How many greats does that ancestor get, how many people stand in that row of your family tree, and roughly when were they born? This calculator answers all three from two numbers: your birth year and how many generations back you want to look.
The birth years are a rough window, not a date. Use them to decide which census, war, or migration to search first.
How to use it
- Enter your own birth year.
- Choose how many generations back: 1 is your parents, 2 your grandparents, 3 your great-grandparents, and so on.
- Read the name of that ancestor, in both the long form and the short "3x great" form.
- Note how many ancestors that generation holds and the rough window when they were born.
Worked examples
Born 1948, 4 generations back
Your great-great-grandparents (2x great-grandparents): 16 people in that generation, 30 ancestors counting every generation from your parents up. Most were born between about 1808 and 1848.
Two greats on a grandparent. Counting parents, grandparents, great-grandparents, and great-great-grandparents gives 2 + 4 + 8 + 16 = 30 people.
Born 1950, 5 generations back
Your great-great-great-grandparents (3x great-grandparents): 32 people in that generation, 62 ancestors counting every generation from your parents up. Most were born between about 1775 and 1825.
Three greats. Most of the 32 were born decades before 1850, the first census to list every free person by name, so for much of their lives the census names only the head of each household.
Born 1955, 8 generations back
Your great-great-great-great-great-great-grandparents (6x great-grandparents): 256 people in that generation, 510 ancestors counting every generation from your parents up. Most were born between about 1675 and 1755.
Six greats. At this depth most American lines reach the colonial era, and the count of 256 is already a ceiling, not a promise.
How many greats?
Your parents are one generation up and your grandparents two. From there, each step adds a "great": great-grandparents are three generations up, great-great-grandparents four. The number of greats is always the number of generations minus two.
Long strings of greats are hard to read, so genealogists shorten them. A great-great-great-grandfather is a 3x great-grandfather, also written 3rd great-grandfather. Both forms mean the same person. The same counting works downward for great-grandchildren.
Why the number of ancestors doubles, and then stops
Everyone has two parents, so each generation back holds twice as many people: 2, 4, 8, 16, and so on, which is 2 raised to the number of generations. Thirty generations back that would be more than a billion people, more than were alive at the time.
The explanation is pedigree collapse. When cousins marry, even distant ones, the same couple fills more than one box in a descendant's tree. The child of first cousins has six great-grandparents rather than eight. In small towns and close-knit communities, collapse often shows up within a few centuries, so treat the calculator's count as the most you could have, not the number you will find.
How many years is a generation?
In family history a generation means the age of a parent when a child was born, and it is longer than many people expect. A study of Quebec genealogies going back to the 1600s, published in the American Journal of Human Genetics in 2000, found an average of about 31.7 years between parent and child.
The gap depends on the line you follow. Through mothers the same study found about 29 years per generation; through fathers about 34.5 years, and straight father-to-son lines averaged about 35 years. Men often married later and fathered children into their forties. If you are tracing a surname line from father to son, expect your ancestor near the earlier end of the window; through a line of mothers, nearer the later end.
Questions people ask
How many years is a generation?
For genealogy, about 30 years is a sound average. A large study of Quebec family trees found about 29 years per generation through mothers and about 35 years through fathers, so a line of fathers reaches further back in time in the same number of generations.
What is my great-great-grandfather's father called?
Your great-great-great-grandfather, also written 3x great-grandfather or 3rd great-grandfather. He is five generations above you.
How many great-great-grandparents do I have?
Sixteen, unless some of your ancestors were related to each other. Each generation back doubles the count: 2 parents, 4 grandparents, 8 great-grandparents, 16 great-great-grandparents.
What does 4x great-grandfather mean?
A grandfather with four greats: great-great-great-great-grandfather. He is six generations above you, one of 64 ancestors in that generation.
How far back is 10 generations?
With generations of about 30 years, roughly 300 years. For someone born around 1950 that reaches the mid-1600s, the first decades of English settlement in New England and Virginia.
How to cite this page
Daily Ancestor. "Generation calculator." Tools. https://dailyancestor.com/tools/generation-calculator. Last checked 2026-10-15.