Possible child blood types from the parents' blood types, with exact probabilities when a parent's genotype is known.
With genotypes unknown, this tool lists possible child types only — it does not invent probabilities, because a type-A parent could be AA or AO. Enter genotypes for exact percentages.
possible child types
How to use this tool
Choose A, B, AB or O for each parent, and their Rh positive or negative status.
The headline lists every ABO type the children could have. Rh possibilities and combined types are shown alongside.
If a parent's genotype is known from testing — AA versus AO, for example — enter it to get exact percentages instead of a possibilities list.
Rare variants, chimerism and Bombay phenotype can break the usual rules, so this is a teaching estimate, not a paternity or medical test.
Formula & worked example
A parent of type A with genotype AO and a parent of type B with genotype BO can have children of all four types, each with 25% probability: AB, A, B and O.
Limitations — read this before you rely on it
With genotypes unknown, percentages would require population frequencies for AA versus AO, which this tool does not invent — so it lists possibilities only. Rare blood variants and the Bombay phenotype (where a person lacks the H antigen) can produce results outside the standard rules.
Frequently asked questions
Under the standard rules, no: two O parents can only pass on O alleles, so all their children are type O.
Yes, if both are AO carriers. Each parent can pass on the O allele, giving a 25% chance of an OO child.
Because a type-A parent could be AA or AO, and those give different child probabilities. Without the genotype, claiming a percentage would be guessing.
Rh status is set by the D antigen. Positive dominates negative, so a child is negative only if it inherits a negative allele from both parents.
It can rule out impossible combinations in clear cases, but it cannot prove parentage. DNA testing is needed for that.