How Much DNA Do First Cousins Share?

Marc McDermott

First cousins share an average of 12.5% of their DNA; or 866 centimorgans. The expected range of shared centimorgans is 396-1397, according to the shared centimorgan project. This percentage is the result of genetic recombination that occurs when parents each pass down half of their DNA to their children.

This amount of DNA is very similar to the amount shared between:

  • Great grandparent and great-grandchild, 
  • Great aunt/uncle and great-niece/nephew
  • Half aunt/uncle and half-niece/nephew

There are also many other possible relationships that fall into this range of shared DNA.

Possible relationships based on 396cm
Possible relationships based on 866cm
Possible relationships based on 1397cm

How much DNA do half first cousins share?

First cousins share an average of 6.25% of their DNA; or 449 centimorgans. The expected range of shared centimorgans is 156-979, according to the shared centimorgan project. 

How much DNA do first cousins once removed share?

First cousins share an average of 6.25% of their DNA; or 433 centimorgans. The expected range of shared centimorgans is 102-980, according to the shared centimorgan project. 

How much DNA do first cousins twice removed share?

First cousins share an average of 3.125% of their DNA; or 221 centimorgans. The expected range of shared centimorgans is 33-471, according to the shared centimorgan project. 

Can first cousins share 25% DNA?

No. First cousins cannot share 25% of their DNA. When two people share this much DNA, the relationship is typically a half-sibling, grandparent, or aunt/uncle.

Is it possible for first cousins to not share DNA?

No, it is not possible for first cousins to not share DNA. It’s only when you get beyond the second cousin level where there’s a small chance of not sharing any DNA. 

References

Painter DNA. Shared cM Project 4.0 Tool v4 with relationship probabilities. Accessed November 12, 2020. https://dnapainter.com/tools/sharedcmv4

Bettinger B. Version 4.0! March 2020 Update to the Shared cM Project!. The Genetic Genealogist. Accessed 13 November 2020. CC 4.0 Attribution License. Data only.

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