The only cousin statistics that acknowledge the differences in paternal and maternal relatives due to recombination rates.

See the relationship probability calculator that’s based on this same model.

I’ve written an article that shows the percentages of shared DNA that a person shares with various relatives and ancestors. These are the only tables or charts of shared autosomal DNA (atDNA) that can be verified by standard deviations from peer-reviewed studies. Other charts or tables have much lower standard deviations, probably because of removing data erroneously thought to be outliers.

Since many in the genetic genealogy community prefer to use centiMorgans (cM) over percentages, and since cM aren’t the same from one platform to another, I’m going to display cM values for each platform on separate pages. The tables here are only for AncestryDNA kits. Many of the values shown here include fully-identical regions (FIR), which can’t be found at AncestryDNA. However, these values could be seen at GEDmatch if an Ancestry user has uploaded there and is comparing to another kit from AncestryDNA. And I do recommend using the total cM for the platform from which you uploaded when converting percentages to cM unless one has made a superkit at GEDmatch.


Table 1. Shared cM of atDNA between siblings for AncestryDNA kits. HIR = ‘half-identical regions,’ where one of the two chromosome homologues matches. FIR = ‘fully-identical regions,’ where both copies of a chromosome match. HIR + FIR = all of the points on chromosomes where two people match once plus all of the points where they match on both copies. HIR counting includes FIR bp, but only counts them as if they’re half-identical.

Table 2. Shared cM between six different types of 3/4 siblings for AncestryDNA kits. All parameters are the same as for Table 1.

Table 3. Shared cM for double first cousins with AncestryDNA kits. All parameters are the same as for Tables 1-2.

Table 4. Shared cM for grandparents and some of their descendants using AncestryDNA total cM. All parameters are the same as for Tables 1-3.

I hope you’ve found these results useful. More will be on the way.

Feel free to ask me about modeling & simulation, genetic genealogy, or genealogical research. And make sure to check out these ranges of shared DNA percentages or shared centiMorgans, which are the only published values that match peer-reviewed standard deviations. That model was also used to make a very accurate relationship prediction tool. Or, try a calculator that lets you find the amount of an ancestor’s DNA you have when combining multiple kits. I also have some older articles that are only on Medium.