Enrichment · Passion Projects · Family history

Second cousin
once removed,
worked out for you.

Count the generations from a shared ancestor down to you and down to each relative. The calculator names the relationship, explains which way a removal runs and gives the DNA you share on average.

Name the relativesWhat you get

The relationship calculator

The worked example is a made-up family below great-grandparents Rose and Tomas. Use first names or initials; nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
The relationship of each relative to you, the generation gap behind any removal, and the average DNA you would share. It prints as a chart and downloads as a spreadsheet.
Who it is for
Students researching family history, families at reunions, genealogy clubs, and history or biology classes studying inheritance.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Up to 40 relatives. Prints a chart; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Name the closest ancestor or couple you share with the relatives.
  2. Type how many generations you are below them.
  3. Add each relative with their generations below, and mark half lines.
  4. Read each relationship and the DNA share.
  5. Print the chart for a family tree or a reunion.

Name the relatives

How relationships are named

Two counts of generations, and a few naming rules.

The worked example: Mia’s son LeoLeo4 belowMia’s sonYou3 belowRose and Tomas’s great-grandchildCousin number3 − 1 = 2ndthe smaller count, less oneRemoved4 − 3 = once2nd cousin once removedThe worked example: Mia’s son LeoLeo4 belowMia’s sonYou3 belowRose and Tomas’s great-grandchildCousin number3 − 1 = 2ndthe smaller count, less oneRemoved4 − 3 = once2nd cousin once removed
Two numbers decide every relationship below a shared ancestor: how many generations down each person is. The smaller sets the cousin number; the gap sets how many times removed.

The rules

When both of you are two or more generations below the ancestor, you are cousins: the cousin number is the smaller count minus 1, and the difference between the counts is how many times removed. When one of you is only one generation down, that person is an aunt or uncle (or grand- and great-grand- versions) to the other's line, and the other is a niece or nephew. Zero generations means the ancestor themself. Half relations share one ancestor but not both members of the couple.

DNA on average

A child inherits half of each parent's autosomal DNA, so a direct ancestor n generations up shares ½^n. Full relations through a couple share 2 × ½^(m + n), so full first cousins share 12.5% and second cousins about 3.1%; half relations share half that. These are averages: from second cousins outward the real figure varies widely, and testing companies report it in centimorgans.

Sources

  1. National Library of Medicine, MedlinePlus Genetics. What is genetic ancestry testing, and how is DNA shared between relatives (medlineplus.gov/genetics).
  2. Bettinger, B. T., and contributors. The Shared cM Project: average shared DNA for known relationships (dnapainter.com and thegeneticgenealogist.com).
  3. National Genealogical Society. Genealogy standards and relationship terms (ngsgenealogy.org).
  4. National Archives. Resources for genealogists: getting started with family history (archives.gov/research/genealogy).

The worked example is made up. Names stay in this browser; first names or initials are enough. Support: team@caveatacademic.com.