How to Use the Child Blood Type Probability Calculator
Human blood type under the ABO system falls into four groups — A, B, AB, and O — determined by one allele inherited from each parent. Since A and B are dominant and O is recessive, a person's visible blood type alone doesn't reveal whether their underlying genotype is homozygous or heterozygous. This calculator takes the blood type of each parent and, using common population statistics, estimates the probability that a child will be type A, B, AB, or O.
For example, if one parent is type A and the other is type B, the child could theoretically end up as A, B, AB, or O — a result that often surprises people expecting a simpler outcome. On the other hand, if both parents are type O, they can only pass on the recessive O allele, so the child will always be type O. Combinations like AB and O parents, who can never have an AB or O child, show how the possible blood types for a child are already constrained by the parents' combination.
Keep in mind that this tool assumes typical population ratios for genotypes that aren't directly known, so the estimated probabilities are a statistical guide and do not replace a medical diagnosis. If your child's blood type seems inconsistent with what should be possible from the parents' types, it's worth double-checking hospital records or requesting a formal blood typing test to confirm the result.
Frequently Asked Questions
This calculator estimates probabilities based on ABO inheritance rules using standard statistical assumptions, since a parent's exact genotype (homozygous or heterozygous) usually isn't known. Actual results can differ.
Yes. Type O comes from two recessive O alleles, so two type-O parents will theoretically always have a type-O child.
No. This tool calculates only the ABO type (A, B, AB, O) and does not include the Rh positive/negative factor.