Double cousin predictions are now updated with many more relationship types and a peer-reviewed data source

  • 3/4 Siblings: Child of your father and maternal aunt
  • 3/4 Siblings: Child of your mother and paternal uncle
  • 3/4 Siblings: Child of your father and maternal half-sister
  • 3/4 Siblings: Child of your father and maternal grandmother (opposite perspective of the immediately above type)
  • 3/4 Siblings: Child of your mother and paternal half-brother
  • 3/4 Siblings: Child of your mother and paternal grandfather (opposite perspective of the immediately above type)
  • Double First Cousins (2x 1C): “Two brothers married two sisters” or “A brother and a sister married a sister and a brother” is how it’s often said
  • 1C + Half- Aunt/Uncle/Niece/Nephew: A cousin has both of the listed relationship types to you
  • 1C + First cousin once removed (1C1R)
  • 1C + Half-1C
  • Double 1C1R: with or without FIR
  • Double Second Cousin (2x 2C): with or without FIR
  • Double 2C1R: with or without FIR
  • Double Third cousins: with or without FIR
FIR probability curves for double cousin relationships at 23andMe

The tools available that use the same peer-reviewed data source are as follows:

This article was previously published here on 9 March 2022.

DNA-Sci — advancing the science of relationship predictions. Feel free to ask a question or leave a comment. And make sure to check out these ranges of shared X-DNAshared atDNA percentages, and shared atDNA centiMorgans. Would you like help visualizing how much DNA full-sibling share? Or, try a tool that lets you find the amount of an ancestor’s DNA you cover when combining multiple kits. I also have some older articles that are only on Medium.