Blood Type Calculator
Estimate possible blood types based on parental blood types and inheritance rules.
How Blood Type Inheritance Works
Blood type is determined by the ABO and Rh systems. The ABO system has three alleles: A, B, and O. The A and B alleles are dominant over O. When both A and B are present, the result is type AB (codominance). The Rh system is simpler: the positive (Rh+) allele is dominant over the negative (Rh-) allele.
Each biological parent contributes one ABO allele and one Rh allele to their child. The child's blood type is the combination of these inherited alleles. This calculator applies standard Mendelian inheritance rules to estimate all possible blood type combinations for a child based on the blood types of both parents.
How to Use the Blood Type Calculator
Select the blood type and Rh factor for each parent from the dropdown menus. The calculator will display all possible blood types their child could inherit, along with the relative probability of each outcome.
For best results, ensure you have confirmed blood type information for both parents. If you only know one parent's blood type, the results will be less specific but may still provide useful possibilities.
Understanding the Results
The calculator shows a list of possible blood types for the child, ordered from most to least likely. Each result includes the ABO type (A, B, AB, or O) and the Rh factor (positive or negative).
Probabilities are based on the genetic combinations possible from the parents' blood types. For example, two O-positive parents can only have an O-positive or O-negative child, while an A-positive and B-positive parent could have a child with any blood type.
These results are estimates based on standard inheritance patterns. They do not account for rare genetic variations or mutations.
Common Blood Type Inheritance Patterns
- Two O parents: Child will always be O (positive or negative depending on Rh factors).
- One A and one B parent: Child could be A, B, AB, or O, depending on the specific A and B subtypes.
- One AB parent: Child cannot be O, because the AB parent always passes either A or B.
- Two Rh-positive parents: Child can be Rh-positive or Rh-negative, since both parents may carry a recessive Rh-negative allele.
- One Rh-negative parent: Child will be Rh-negative only if the other parent also carries an Rh-negative allele or is Rh-negative.
Limitations of Blood Type Prediction
This calculator provides genetic probabilities, not guarantees. Actual blood type is determined by laboratory testing. Rare blood type variants, such as the Bombay phenotype or cis-AB, are not accounted for in standard inheritance models. If you need definitive blood type information for medical purposes, consult a healthcare provider and request a blood test.
The calculator assumes standard Mendelian inheritance and does not consider non-paternity, chimerism, or other rare genetic scenarios.
FAQ
Can two O-positive parents have an A-positive child?
No. Two O parents can only pass the O allele to their child. Since O is recessive, the child will always be type O. The Rh factor can be positive or negative depending on the parents' Rh genotypes.
What does it mean if my child has a blood type neither parent has?
This is possible when both parents carry recessive alleles. For example, two A-positive parents can have an O-positive child if both carry the recessive O allele. Similarly, two Rh-positive parents can have an Rh-negative child if both carry the recessive Rh-negative allele.
Is blood type inheritance 100% predictable?
No. While standard inheritance patterns cover the vast majority of cases, rare genetic variations can produce unexpected results. The only way to confirm blood type is through a medical blood test.
Why does the calculator show multiple possible blood types?
Because blood type inheritance depends on the specific combination of alleles each parent carries. For example, an A-positive parent could be AA or AO for ABO, and Rh+/Rh+ or Rh+/Rh- for Rh. The calculator accounts for all possible combinations and shows every blood type that could result.