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.

Can two O parents have a non-O child?

No. O is recessive, so two O parents can only pass O alleles and the child must be type O. The calculator reflects this — only O appears in the results.

Can A and B parents have an O child?

Yes, if both parents carry a hidden O allele (genotype AO and BO). Their child could be A, B, AB or O. The calculator shows all four possibilities with probabilities.

Why are the percentages approximate?

A parent with type A, B or Rh-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.

How is the Rh factor predicted?

Rh-positive is dominant. A positive parent is assumed equally likely to be ++ or +-, and a negative parent is always --. The tool combines the parents to give the chance of a positive or negative child.

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.

Is anything uploaded?

No. The calculation runs entirely in your browser; nothing is sent anywhere.

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. It is a teaching tool for ABO and Rh genetics.

How it works

Each ABO phenotype maps to its possible genotypes — for example type A is either AA or AO. The calculator forms a Punnett-square cross of every parent genotype combination, tallies the child phenotypes, and assumes each parental genotype is equally likely (since a hidden recessive O can’t be seen without a test). It does the same for Rh, treating a positive parent as equally likely ++ or +−, then multiplies the ABO and Rh probabilities together for the full blood type.

Example

Parent 1 is A+ and Parent 2 is B+. Both could carry an O allele, so the ABO cross can yield A, B, AB or O, and Rh can be + or −:

Possible child type	Approx. probability
AB+	highest band
A+ / B+	moderate
O+	lower
any − type	smaller (needs both Rh parents to carry −)

Because genotypes are assumed equally likely, the percentages are estimates. This is educational only — not a paternity or medical test — and runs entirely in your browser.