🩸 Blood Type Calculator
Select each parent’s ABO and Rh genotype to see the probability of each possible blood type for their child.
How blood type inheritance works
A child’s ABO blood type (A, B, AB or O) and Rh factor (positive or negative) are each inherited independently, one allele from each parent, following standard Mendelian dominant/recessive genetics. The A and B alleles are co-dominant and both dominant over O, while the Rh-positive allele is dominant over Rh-negative.
How this calculator works
Because a person with Type A or Type B blood can be homozygous (e.g. AA) or carry a hidden O allele (e.g. AO), this calculator asks for each parent’s full genotype rather than just their visible blood type. It then builds a Punnett square for the ABO alleles and another for the Rh alleles, and combines the two independently to estimate the probability of each of the eight possible blood types (A+, A-, B+, B-, AB+, AB-, O+, O-) for their child.
- ABO alleles: A and B are co-dominant; O is recessive
- Rh alleles: positive (+) is dominant over negative (-)
- ABO type and Rh factor are inherited independently
This tool is for general educational and family-planning interest only. If you do not know a parent’s exact genotype, results are an estimate; a lab blood test is the only way to confirm actual blood type.