How Many Ancestors Do I Have

Enter your birth year and how many years you assume per generation. You get the number of ancestors in any generation, the running total, a chart and a table.

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The calculator answers the question “how many ancestors do I have” for any number of generations back. Enter your birth year, the average number of years between generations and either the number of generations or a year you want to reach. You get the number of ancestor places in that generation, which doubles every time, the total from your parents up to it, what that generation is called and the year its members were born, roughly. A bar chart shows the doubling and a table lists generations 1 to 40. A separate section explains why the real number is smaller, because the same ancestors appear in several places. Big numbers up to generation 100 are exact, and nothing leaves your browser.
How many ancestors do i have example

How to use the ancestors calculator

  1. Type your year of birth into “Your birth year”.
  2. Under “Years per generation” enter the average age at which people in your family had children, from 15 to 40, or press one of the buttons 20, 25, 30 or 35.
  3. Under “Go back by” choose “Number of generations” or “Target year”. With the first, type the count into “Generations back”. With the second, type a year into “Go back to the year” and the calculator picks the nearest generation.
  4. Read the tiles. “Ancestor places in this generation” is the main number. “Generation” gives the name, for example 8th great-grandparents. “All ancestor places from your parents to this generation” is the running total. “Born around” is your birth year minus the generations.
  5. Look at the bar chart of the first 16 generations at most. The highlighted bar is your generation, and each bar is twice the one before.
  6. Scroll to the table “Generations 1 to 40”. The chosen row is highlighted. Press “Copy table” or “Download CSV” to take the numbers away.
  7. In the last section, type your own figure under “People alive at that time”. The page shows the first generation that has more ancestor places than people. The figure already there is only an example.

How many ancestors do I have?

Everyone has two parents, four grandparents and eight great-grandparents, so generation n back has 2 to the power n ancestor places. Generation 10 has 1,024 places and generations 1 to 10 together have 2,046, because the total of all generations up to n is 2 to the power n+1, minus 2. You are not counted. Generation 40 has 1,099,511,627,776 places and generation 100 has 1,267,650,600,228,229,401,496,703,205,376.

How many generations back is a given year?

The calculator divides the years between your birth year and the target year by the years per generation and rounds to the nearest whole generation. Born in 1990 with 25 years per generation, the year 1740 is 250 years back, which is generation 10. The “Born around” year is only an average. Real parents are born in a range of years.

What is pedigree collapse?

The numbers count places, not different people. If two cousins marry, their shared grandparents are the child’s great-grandparents and fill four places with only two people. Because the count doubles each time, it grows far beyond the number of people alive in earlier centuries, so places must be shared. With an example of 1,000,000 people, generation 20 is the first with more places than people: 1,048,576 places, at least 48,576 of them repeated. Supply your own figure to test other cases. The calculator cannot know how many repeats your own tree has.

Why does the number of ancestors grow so fast?

Each person in a generation brings two parents into the next one, so the count doubles. Ten generations give about a thousand places, twenty give over a million (1,048,576) and thirty give over a billion (1,073,741,824). With 25 years per generation, thirty generations reach back about 750 years.

What are the ancestors in each generation called?

Parents, grandparents and great-grandparents are generations 1 to 3. After that the names count the greats: generation 4 is 2nd great-grandparents, generation 5 is 3rd great-grandparents, and so on.

Frequently asked questions

How many ancestors do I have after 10 generations?

Generation 10 has 1,024 places, and all ten generations together have 2,046. Your birth year only changes the years shown, not the counts.

How many grandparents and great-grandparents do I have?

You have 4 grandparents and 8 great-grandparents. Generation 4 has 16 places and generation 5 has 32.

Why is the real number lower than 2 to the power n?

Because the same person can fill several places. Cousins who marry, or families that stayed in one village, make lines meet. The number on this page is the largest possible.

How many years should I use per generation?

It is the average age of parents at the birth of the child in your own line. The buttons offer 20, 25, 30 and 35, and any whole number from 15 to 40 works. Use the spread of the dates in your tree if you have them.

Can it go back more than 40 generations?

Yes. The tiles accept up to 100 generations, the table lists the first 40 and the chart the first 16.

What does the Target year option do?

You type a year and the calculator finds the nearest generation to it. It does not know who lived then. The result is the count of places in that generation.

Is my birth year stored?

No. The page keeps the numbers in the address so you can share a result, and nothing is sent to a server.