Blood Type Calculator
A type A parent and a type B parent can have a child with any of the four ABO blood types: A, B, AB, or O. This blood type calculator uses standard Mendelian genetics for the ABO gene and the Rh factor to list every blood type a child could possibly inherit from two parents. Enter each parent's ABO type and Rh factor to see the full set of possible outcomes, plus the types that are ruled out.
Quick answer
The ABO gene has three alleles. A and B are codominant, and O is recessive to both.
What this tells you
- •The ABO gene has three alleles. A and B are codominant, and O is recessive to both.
- •A parent with type A or type B blood could carry a hidden O allele, so this tool lists every outcome consistent with each parent's phenotype.
- •Rh+ is dominant over Rh-. Only two Rh- parents guarantee an Rh- child. Any Rh+ parent could carry a hidden Rh- allele.
How to Use
- 1Select the first parent's ABO blood type: A, B, AB, or O.
- 2Select the first parent's Rh factor: positive or negative.
- 3Select the second parent's ABO blood type and Rh factor.
- 4Calculate to see every possible blood type for their child and which types are ruled out.
How It Works
Formula
ABO: A and B alleles are codominant, O is recessive
Rh: Rh+ is dominant, Rh- is recessive
Example: type A x type B parents can produce A, B, AB, or O offspringEach parent passes on one ABO allele and one Rh allele to a child. Because a type A or type B phenotype can come from two different genotypes (homozygous or carrying a hidden O allele), this calculator considers every genotype consistent with the phenotype you select and lists the union of possible offspring types. The same logic applies to Rh factor, where an Rh+ parent may or may not carry a hidden Rh- allele.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Type A and type B parents
Both parents could carry a hidden O allele, and both are Rh+, so a hidden Rh- allele is possible on either side. That combination allows every ABO and Rh outcome.
AB type and O negative parents
A type AB parent always passes an A or a B allele, never O, so an O child is impossible. A type O parent never passes an A or B allele, so an AB child is also impossible.
Two O negative parents
Type O is a recessive ABO genotype and Rh- is a recessive Rh genotype, so two O- parents can only pass on O and Rh- alleles.
ABO Parent Combinations and Possible Offspring
Possible ABO types a child can inherit from each combination of parent phenotypes.
| Parent 1 | Parent 2 | Possible child ABO types |
|---|---|---|
| O | O | O |
| A | O | A, O |
| B | O | B, O |
| AB | O | A, B |
| A | A | A, O |
| A | B | A, B, AB, O |
| A | AB | A, B, AB |
| B | B | B, O |
| B | AB | A, B, AB |
| AB | AB | A, B, AB |
Rh factor is calculated separately. An Rh- child is only guaranteed when both parents are Rh-.
Common mistakes
- Assuming a type A or type B parent's exact genotype is known. Both phenotypes can hide a recessive O allele.
- Assuming an Rh+ parent cannot have an Rh- child. A heterozygous Rh+ parent can pass on the recessive allele.
- Treating this tool as a paternity or maternity test. Matching blood types does not confirm a biological relationship, and mismatched types do not rule one out on their own.
Limitations
This calculator assumes standard Mendelian inheritance for the ABO gene and the Rh factor and lists every outcome consistent with each parent's stated phenotype, since exact genotype (homozygous or heterozygous) usually is not known from blood type alone. It does not model rare inheritance patterns such as the Bombay phenotype, cis-AB, weak D variants, chimerism, or other minor blood group systems. The result shows what is genetically possible, not a guarantee of what any specific child will inherit.