Genealogy Calculators

DNA matching, ancestor counts and relationship estimation. 10 calculators for family historians. The inheritance mechanics underneath sit under Biology.

Centimorgan (cM) relationships is the page to read before trusting any match list, because the bands overlap badly. A 200 cM match could be a half first cousin, a first cousin twice removed, or a second cousin, and the total will not separate them. The close relationships collapse together too: aunt, uncle, grandparent and half sibling all sit between 1,300 and 2,300 cM, and the DNA cannot tell them apart at all. What does separate a parent from a full sibling is not the total but the fully identical regions, of which a parent has none.

Pedigree collapse explains why doubling ancestors every generation stops working. Thirty generations back is over a billion theoretical slots, and there were nowhere near a billion people alive in 1100. Cousins married, lineages crossed, and most of those slots hold the same people twice.

Every figure here uses the 6,800 cM autosomal genome, not the 7,400 version that folds in the X chromosome.