Blood Type (ABO & Rh) Calculator
Enter parents’ blood types
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Use this Blood Type Calculator to estimate possible ABO and Rh blood types of a child from the reported blood types of both parents.
How Blood Type Inheritance Works
A child inherits one ABO allele from each parent. The main teaching model uses three alleles:
- A
- B
- O
A and B are codominant, while O is recessive. This means a person with type A may have an AA or AO genotype, and a person with type B may have BB or BO.
The calculator also estimates Rh positive or negative outcomes using a simplified inheritance model.
Example
If both parents are O−, standard simplified inheritance assumes both pass an O allele and an Rh-negative allele.
The expected child blood type is therefore O−.
For parents with A, B, or Rh-positive blood types, hidden genotypes can allow several possible outcomes.
Important Note
This calculator shows possible inheritance outcomes, not a confirmed blood type. Exact probabilities may be uncertain when the parents’ underlying genotypes are unknown.
Do not use it for paternity testing, transfusion compatibility, or pregnancy-related Rh decisions. Laboratory blood typing and appropriate medical testing are required for those purposes.