How to use the baby blood type predictor
- Select the father's ABO blood type (A, B, AB or O) and Rh factor.
- Select the mother's ABO blood type and Rh factor the same way.
- Press Calculate to see every blood type genetically possible for your baby.
A person's blood type test only shows their phenotype (A, B, AB or O), not their full genotype. A type-A parent could be genetically AA or AO — and that hidden difference changes what's possible for their child. The calculator shows every outcome consistent with your inputs.
How ABO blood type is inherited
Blood type is set by a single gene with three common alleles: A, B, and O. A and B are co-dominant — if you inherit one of each, you're type AB, with both traits expressed rather than one masking the other. O is recessive to both — you need two O alleles to be type O, since a single A or B allele will dominate. This ABO inheritance chart is one of the most well-established patterns in classical genetics.
ABO inheritance chart
| Parent 1 | Parent 2 | Possible child types |
|---|---|---|
| O | O | O only |
| O | A | A or O |
| O | B | B or O |
| O | AB | A or B |
| A | A | A or O |
| A | B | A, B, AB or O |
| A | AB | A, B or AB |
| B | B | B or O |
| B | AB | A, B or AB |
| AB | AB | A, B or AB |
How Rh factor (positive/negative) is inherited
Rh-positive is dominant over Rh-negative. A child is only Rh-negative if they inherit a negative allele from both parents — which means two Rh-positive parents can still have an Rh-negative baby if both happen to be silent carriers, much like the recessive pattern seen in eye and hair color inheritance.
Terms related to blood type prediction
- ABO gene
- The single gene on chromosome 9 that determines A, B, AB or O blood type based on which alleles a person inherits.
- Co-dominance
- When two different alleles are both fully expressed at once — the reason AB blood type shows both A and B markers rather than one overriding the other.
- Rh factor
- A separate protein marker (positive or negative) inherited independently of ABO type, most relevant during pregnancy for Rh compatibility between mother and baby.
- Universal donor / recipient
- O-negative blood is considered the universal donor type; AB-positive is considered the universal recipient type, relevant in transfusion medicine.
- Genotype (blood type)
- The specific pair of alleles a person carries — for example AO or AA — which isn't distinguishable from a standard blood type test alone.
Limitations of blood type prediction
- Genotype is hidden — a blood type test alone can't tell you if a type-A or type-B parent is heterozygous or homozygous.
- This tool shows possibilities, not odds — without genotype testing, precise percentages would be misleading.
- Rare subtypes exist — the Bombay phenotype and other rare variants aren't reflected in this simplified model.
Frequently asked questions
No. Type O is genetically recessive with no dominant allele to mask, so two type-O parents can only have type-O children.
Yes, in some combinations. For example, two type-A parents who are each secretly carrying an O allele can have a type-O child, since O is recessive and can hide for a generation.
Rh-positive is dominant. A child is Rh-negative only if they inherit the negative allele from both parents — meaning both parents must carry it, even if one or both are Rh-positive themselves.
Blood type depends on each parent's full genotype (e.g., whether a type-A parent is AA or AO), which isn't visible from blood type alone. The calculator shows every type genetically possible for your specific inputs.
Occasionally people assume this, but it's rarely reliable — recessive alleles can produce a child's blood type that looks surprising on paper but is entirely consistent with the parents' true genetics.
If a mother is Rh-negative and the baby is Rh-positive, doctors routinely manage this with a standard treatment (anti-D immunoglobulin) — it's a well-understood, well-managed situation, not a rare emergency.