Blood Type Calculator
The Blood Type Calculator is a free online ABO inheritance tool. Select the father's and mother's blood types to see every blood type their child could have, along with the probability of each. It also includes a complete inheritance reference table, genotype explanations (such as AA and AO), and notes on the Rh factor.
The lookup runs entirely in your browser — no personal information is submitted, and no registration is needed. It is useful for expecting parents curious about their baby's possible blood type, students learning Mendelian genetics, and anyone interested in how blood types are inherited.
How to Use
- Select the father's ABO blood type.
- Select the mother's ABO blood type.
- Click the Calculate button.
- Review the possible blood types, their probabilities, and any special notes.
FAQ
Is the blood type calculator free?
Yes, completely free with no registration — just pick the parents' blood types to see the results instantly.
How does blood type inheritance work?
ABO blood type is determined by a pair of alleles: A and B are dominant, O is recessive. Each parent passes one allele to the child. For example, a type A parent may be AA or AO; paired with a type O parent (OO), the child can be either type A or type O. The tool derives probabilities from the theoretical mix of these genotype combinations.
Why can a child have a different blood type from both parents?
Because type A and B parents can carry a hidden recessive O allele. An AO father and BO mother, for instance, can have children of type A, B, AB, or O. The probabilities shown follow Mendelian ratios, so a child's type differing from both parents is completely normal.
Can the results be used to prove paternity?
No. Rare genetic variants such as cis-AB and the Bombay phenotype can break the usual inheritance patterns, and a matching blood type never proves a biological relationship. The results are for reference and education only — paternity questions require professional DNA testing.