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Cousin Relationship Calculator (Degree & Removed)

Work out how two people are related from the number of generations each is below their most recent common ancestor: first, second or third cousin, once or twice removed, the genealogical degree of kinship, the expected shared DNA in centimorgans and percent, and the canon-law and civil-law degrees.

Generations from person A down from the common ancestor(s)

Generations from person B down from the common ancestor(s)

Common ancestors

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How it works

Cousin number = min(gA, gB) − 1; removed = |gA − gB|; civil degree = gA + gB; canon degree = max(gA, gB); expected shared DNA = (½)^(gA + gB − 1) for full relations (halve for half)

Cousin terminology is a code for two numbers: how many generations the more closely related person is below the shared ancestral couple (which sets first, second, third cousin) and how many generations the two people differ by (which sets "once removed", "twice removed"). Your first cousin's child is your first cousin once removed; your parent's first cousin is also your first cousin once removed, from the other direction. The same two numbers give the legal degrees of kinship used in marriage prohibitions and intestacy law — the civil (Roman) system counts every step up and down, the canon system only the longer branch — and, because each generation halves the DNA inherited from an ancestor, they predict how much DNA the two people should share in a genetic test.

Worked example

If A is a great-grandchild (3 generations) and B a great-great-grandchild (4 generations) of the same couple, they are second cousins once removed: second because the closer one is 3 generations down (3 − 1 = 2), once removed for the one-generation difference. Civil degree 7, canon degree 4, and they should share about 1.56% of their DNA, roughly 106 cM.

Frequently asked questions

What is a "double cousin"?

When two siblings marry two siblings, their children share both sets of grandparents and are double first cousins — related through two lines, sharing about 25% DNA like half-siblings.

Are second cousins allowed to marry?

In almost every jurisdiction yes; first-cousin marriage is legal in most of the world and in about half of US states. Laws are framed in degrees of kinship, which is why the civil/canon degree matters.

Related calculators

Shared DNA (centimorgans) to Relationship Calculator

Enter the centimorgans shared with a DNA match to see the percentage of DNA shared, the most likely relationships and which are ruled out, using published shared-cM ranges, plus the segment count and largest-segment sanity check and what to compare next.

Ancestors per Generation & Generation Year Calculator

How many ancestors you have at each generation (2ⁿ) and in total, roughly when they were born, how many generations back a given year is, who any ahnentafel number is (relationship, side, sex, path), when pedigree collapse sets in, and how many of those ancestors actually passed you DNA.

Age Difference Calculator

Find the exact age gap between two people from birth dates, birth years or ages — in years, months and days, decimal years, months, weeks and days — plus who is older, both ages on any date, the age ratio, when one was twice the other’s age and a milestones table.

Date Difference Calculator

Count the exact days between two dates — optionally including the end date — and see the gap in years, months and days, weeks, hours and minutes, plus working days with weekends and US, Mexican or Spanish holidays left out.

This calculator is for educational purposes. Double-check important results before acting on them.