Blood Type Calculator
Choose each parent's ABO genotype to see the possible child blood types and their odds.
ABO blood type is set by three alleles: A and B are codominant and both dominant over O. A child inherits one allele from each parent. Crossing an A-carrier (genotype AO) with a B-carrier (BO) can give AB, A, B or O — each with 25% probability, showing all four types are possible.
How to Use This Calculator
Choose each parent's ABO genotype. Because blood type A can come from either the AA or AO genotype (and B from BB or BO), using the genotype rather than just the blood type gives an exact answer. The calculator crosses the two and reports every possible child blood type with its probability.
If you only know a parent's blood type, an A parent is AA or AO, a B parent is BB or BO, an AB parent is AB, and an O parent is always OO.
How the Calculation Works
Each parent passes one of their two ABO alleles, giving four equally likely allele pairs — a Punnett square for the ABO gene. The child's blood type follows the pairing: two O alleles give type O; an A with an O (or two A's) gives type A; a B with an O (or two B's) gives type B; and an A with a B gives type AB.
A and B are codominant, so inheriting both produces AB rather than one masking the other, while O is recessive to both.
combine one allele from each parent; A,B dominant over O; A,B codominant
Worked Example
Cross AO × BO. The four allele combinations are AB, AO, BO and OO. Translating to blood types: AB is type AB, AO is type A, BO is type B, and OO is type O.
So the child could be AB, A, B or O — each with a 25% probability. This is the well-known case where two parents can have a child of any ABO type.
Assumptions and Limitations
- Covers the ABO blood group only, not the Rh (+/−) factor
- Uses genotypes for an exact result; blood type alone can be ambiguous
- Assumes standard ABO inheritance (rare exceptions exist)
- Probabilities are per child and independent for each pregnancy
When to Use a Blood Type Calculator
Biology students and curious parents use this to predict a child's possible ABO blood types from the parents' genotypes. Run it for genetics coursework or to satisfy a family curiosity about inheritance. It shows the possible types and their probabilities — an educational prediction, not a paternity or medical test.
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Open calculator →Frequently Asked Questions
How is blood type inherited?
Each parent passes one ABO allele — A, B or O. A and B are codominant and both dominant over O, so the child's type depends on the pair inherited: AB, A, B or O.
Can two type-A parents have a type-O child?
Yes, if both are genotype AO. Each can pass the O allele, giving a 25% chance of an OO (type O) child. Two AA parents cannot.
Why use genotype instead of blood type?
Because type A can be AA or AO, and type B can be BB or BO. The genotype removes that ambiguity and gives exact child probabilities.
Does this include the Rh factor?
No, it covers the ABO group only. The Rh (positive/negative) factor is inherited separately, with Rh-positive dominant over Rh-negative.
Are the probabilities per child?
Yes. Each pregnancy is independent, so the percentages apply to each child separately, not across a family.
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