Family / Relationships
Cousin Calculator: Relationship Chart and Shared DNA
Enter two generation distances to a nearest common ancestor, or select a relationship-chart cell. Find cousin degrees, removals, half relations and expected shared DNA.
Cousin Calculator: Relationship Chart and Shared DNA: For cousins, degree is the smaller generation distance minus one, and removal is the difference. Handles siblings, aunts and uncles, nieces and nephews, and direct ancestry separately. Numeric entry supports 0 to 12 generations; the chart shows 1 to 6. Expected autosomal sharing assumes unrelated founders and a single ancestral path or couple. Runs 100% locally in your browser with zero server file uploads.
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- Home & family tools
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- In your browser
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- Free · no sign-up
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- Ready to use
Runs entirely in your browser
Count generations to the nearest common ancestor: parent = 1, grandparent = 2, great-grandparent = 3. Use 0 when one person is the ancestor.
Their relationship to me
first cousin once removed
This is an expected autosomal DNA coefficient, not a DNA test prediction. Real centimorgan (cM) sharing varies widely; distant relatives may share no detectable DNA. The calculation assumes unrelated ancestors and no additional shared family lines.
Relationship chart and naming rules
FamilySearch explains cousin degrees and removals: https://www.familysearch.org/en/blog/cousin-chart . The explicit test chart follows the Baltimore County Genealogical Society chart, with aunt/uncle versus niece/nephew direction made explicit: https://www.baltimoregenealogysociety.org/BCGS_Cousin_Chart.html . Great/grand alternatives: https://help.ancestry.com/hc/en-us/articles/53933314142483-Family-Relationship-Terms .
Expected shared DNA
For collateral relatives, the coefficient is 2 raised to 1 minus the sum of both distances; one shared ancestor halves it. For direct ancestry it is 2 raised to minus the distance. First cousins share an expected 12.5%: https://www.genomicseducation.hee.nhs.uk/glossary/third-degree-relative/ . Coefficient table and path rule: https://isogg.org/wiki/Coefficient_of_relationship . These are averages, not individual cM predictions.
How to use it
- Count each person's generations to the nearest common ancestor: parent is 1, grandparent is 2 and great-grandparent is 3.
- Enter the two distances or choose their intersection on the chart. Select one shared ancestor for a half relationship.
- Read their relationship to you, alternative great/grand terms and the expected shared DNA percentage.
Privacy & limitations
All calculations run locally in your browser. Nothing is uploaded.
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Frequently asked questions
What does once removed mean?
It means the relatives are one generation apart in their descent from the shared ancestor. It does not describe their age difference.
How do half relationships work?
Collateral relatives with one shared ancestor rather than a shared couple are half relatives, such as half-siblings or half first cousins. Their expected DNA coefficient is half the full relationship. Direct ancestry is never a half relationship.
Is a grandaunt the same as a great-aunt?
Both names are used for a grandparent's sister. The calculator shows both naming styles, adding great prefixes for further generations.
Will a DNA test show this percentage?
Not necessarily. These are theoretical autosomal averages; real cM sharing varies widely and distant relatives may share no detectable DNA. Multiple shared family lines, pedigree collapse and endogamy are not modelled.
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