Predict a baby's possible ABO and Rh blood types from both parents' types, with the probability of each and which types cannot occur.
A genetic probability estimate assuming standard ABO/Rh inheritance — general information, not medical advice.
About this tool
The Child Blood Type Predictor estimates which ABO and Rh(D) blood types a child could inherit from two parents, and how likely each one is. Pick each parent's blood type (A, B, AB or O) and Rh factor (positive or negative); the calculation runs entirely in your browser and nothing is stored or uploaded.
Each visible blood type (phenotype) maps to the genotypes that can produce it: A → {AA, AO}, B → {BB, BO}, AB → {AB}, O → {OO}, assuming the possible genotypes are equally likely. The tool takes a Punnett-square cross of the ABO alleles each parent can pass, maps every offspring allele pair back to a phenotype (A+B → AB, otherwise A → A, B → B, O+O → O), and adds up the probabilities. Rh is handled the same way — Rh+ → {++, +−}, Rh− → {−−} — and any offspring carrying a + allele is Rh positive. The ABO and Rh results are combined by multiplication because the two systems are inherited independently.
Results are shown as each possible type with its chance, most-likely first, plus the types that are impossible for this pairing. For example an AB parent with an O parent can have A or B children but never O or AB, and two O parents can only have O children.
Frequently asked questions
How are the probabilities worked out?
By a Punnett cross. Each parent phenotype expands to its equally-likely genotypes; each genotype passes one of its two alleles with probability one-half. Crossing both parents' alleles and grouping by resulting phenotype gives the ABO percentages, and the same is done for Rh.
Why is a type marked impossible?
If no combination of alleles the parents can pass produces that phenotype, its probability is zero. For instance an AB × O pairing can never yield O or AB, because AB parents pass A or B and O parents pass only O.
Are these exact odds for my child?
No — they are a genetic probability estimate assuming standard ABO/Rh inheritance and equally likely parental genotypes. Rare subgroups (like the Bombay phenotype) and weak-D variants are not modelled. It is general information, not medical advice.
Why combine ABO and Rh by multiplying?
The ABO gene and the RhD gene sit on different chromosomes and are inherited independently, so the chance of a combined type such as A+ is simply the chance of A multiplied by the chance of Rh positive.