How is blood type inherited?

ABO blood type comes from two alleles, one from each parent, chosen from A, B and O. A and B are co-dominant and O is recessive, so an A parent may secretly carry an O allele. The Rh factor is inherited separately, with positive dominant over negative.

Why are the percentages approximate?

A parent with type A, B or AB positive can be homozygous or carry a hidden recessive allele. Without a genetic test the exact genotype is unknown, so the calculator assumes each possibility is equally likely and averages the outcomes.

Can this prove paternity?

No. Blood type can sometimes rule a parent out, but it can never prove parentage. This tool is for education only and is not a paternity or medical test.

Blood Type Inheritance Calculator

Predict a child’s blood type

Enter both parents’ ABO group and Rh factor, and this calculator shows every blood type a child could inherit along with an approximate probability for each.

ABO type is set by two alleles (A, B or O) — one from each parent — while the Rh factor is inherited separately, with positive dominant over negative. Because a positive or A/B parent may carry a hidden recessive allele, the percentages are estimates. This is an educational tool, not a paternity or medical test, and runs entirely in your browser.