Uses Japanese population ABO genotype frequency statistics as conditional probabilities to calculate the probability of a baby's blood type from both parents' ABO blood types.
If the calculator does not appear, enable JavaScript and reload. The reference information and official links below still work.
Calculation basis and official references
Reviewed on:
This calculator is not a diagnosis, treatment plan, or prescription. Please consult a qualified clinician about your medical decisions.
Formula basis
For each parent's phenotype, conditional genotype probabilities are taken from Japanese population ABO genotype frequency data (based on Fujita et al. 1978: OO 29%, AA 8%, AO 31%, BB 3%, BO 19%, AB 10%) — e.g. for phenotype A, P(AA)=8/39 and P(AO)=31/39; for phenotype B, P(BB)=3/22 and P(BO)=19/22; O is always genotype OO and AB is always genotype AB. For every combination of parental genotypes, each of the 2x2 possible allele pairings from the two parents is assigned equal probability (0.25), the resulting child phenotype is determined by ABO dominance, and probabilities are summed per phenotype across all combinations.
Calculation method
Uses Japanese population ABO genotype frequency statistics as conditional probabilities, combined with Mendelian segregation, to estimate the ABO blood type distribution of a baby from both parents' blood types.
Exclusions and checks required
Extremely rare exceptions such as "cis-AB" (A and B genes on the same chromosome) are not modeled.
The genotype frequencies used are population-level Japanese statistics, not the parents' actual laboratory-confirmed genotypes, so the result does not guarantee the real child's blood type.
Example input:：Father is type A, mother is type O
p1
A
p2
O
This statistical model gives an expected split of 40% type O and 60% type A, but the actual blood type of a real child is not determined by this ratio.
Who is this calculator for? Probability of a Baby's Blood Type
Uses Japanese population ABO genotype frequency statistics as conditional probabilities to calculate the probability of a baby's blood type from both parents' ABO blood types.
What values should I enter?
Applies to: Blood pressure & blood
How should I interpret this estimate?
Uses Japanese population ABO genotype frequency statistics as conditional probabilities, combined with Mendelian segregation, to estimate the ABO blood type distribution of a baby from both parents' blood types.
How to use
Enter your input values and press Calculate.
Review the result and compare it with expected context.
For each parent's phenotype, conditional genotype probabilities are taken from Japanese population ABO genotype frequency data (based on Fujita et al. 1978: OO 29%, AA 8%, AO 31%, BB 3%, BO 19%, AB 10%) — e.g. for phenotype A, P(AA)=8/39 and P(AO)=31/39; for phenotype B, P(BB)=3/22 and P(BO)=19/22; O is always genotype OO and AB is always genotype AB. For every combination of parental genotypes, each of the 2x2 possible allele pairings from the two parents is assigned equal probability (0.25), the resulting child phenotype is determined by ABO dominance, and probabilities are summed per phenotype across all combinations.