Blood type calculator.
Predict a child’s possible blood types from the parents. Choose each parent’s ABO group and Rh factor, and the calculator shows the blood types the child can and cannot have.
Parents blood types
LiveABO follows codominant A and B with recessive O. Rh positive is dominant. Results show every type the child could have, not exact odds.
Possible child ABO
A, B, AB or O
possible blood groups
Shows genetically possible types, not a paternity test or medical diagnosis. Rare exceptions exist. Calculations run in your browser; nothing is stored.
How it works
One allele from each parent
Blood type comes from two systems. In the ABO system there are three alleles: A and B are codominant and O is recessive, so an A parent can be AA or AO. A child inherits one ABO allele from each parent, which sets whether they are A, B, AB or O.
The Rh factor is separate: Rh positive is dominant over Rh negative, so two positive parents can still have a negative child if both carry the negative allele. The calculator combines both to list every type the child could have.
Reference
Parent groups to child.
Possible child ABO groups for common parent combinations.
| Parents (ABO) | Possible child |
|---|---|
| O and O | O |
| A and O | A, O |
| A and B | A, B, AB, O |
| AB and O | A, B |
| AB and AB | A, B, AB |
The full guide
The complete guide to blood type inheritance.
How ABO and Rh are inherited, what a child can and cannot be, and the limits of the prediction.
The ABO system
The ABO gene has three alleles. A and B each produce their antigen and are codominant, so inheriting both gives type AB. O produces no antigen and is recessive, so type O needs two O alleles. This means an A person is genetically AA or AO, and a B person BB or BO.
A child gets one ABO allele from each parent, and the pair they inherit decides their group.
The Rh factor
The Rh system is inherited separately. The Rh positive allele, D, is dominant, and Rh negative, d, is recessive. So Rh positive parents may each carry a hidden negative allele, and two positive parents can have a negative child if both pass on d.
Two Rh negative parents can only have Rh negative children, since neither carries the dominant allele.
What a child can and cannot be
Because alleles combine in set ways, some parent pairs rule out certain types. Two O parents can only have O children; an AB parent can never have an O child. The calculator lists both the possible types and any that are impossible.
Where a parent could carry a hidden O, more types open up, which is why an A and B pair can produce any of the four groups.
Limits of the prediction
This shows what is genetically possible, not the exact probability, since you usually do not know whether a parent is homozygous or heterozygous. It is also not a paternity test, and very rare genetic exceptions exist.
Use it to understand inheritance, not to make medical or legal decisions, which need proper testing.
The formula
A and B
over O.
Each parent passes one ABO allele; A and B are codominant, O recessive. Rh positive is dominant.
Try Punnett squares ›# ABO alleles
A, B codominant; O recessive
child = one allele from each parent
# Rh
Rh+ (D) dominant over Rh- (d)Questions
Blood type questions.
How do I work out my child’s blood type?
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Each parent passes one ABO allele and one Rh allele. The combinations set the possible groups. Choose both parents’ types above and the calculator lists every blood type the child could have.
Can two O parents have a non-O child?
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No. Type O is recessive, so two O parents carry only O alleles and can only have O children.
Can an A and B couple have an O child?
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Yes, if both carry a hidden O allele (AO and BO). An A and B pair can have a child of any group: A, B, AB or O.
Can Rh positive parents have an Rh negative child?
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Yes, if both carry the recessive Rh negative allele. Two Rh negative parents, though, can only have Rh negative children.
Is this blood type calculator a paternity test?
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No. It shows what is genetically possible, not exact odds, and rare exceptions exist. It is not a paternity test or medical diagnosis.
About the developer
Jean Borg
Jean builds and maintains every calculator on freecalculators.pro from Malta, with a focus on tools that are fast, free and show their working. The blood type calculator uses standard ABO and Rh inheritance and is for education, not medical or paternity decisions.