Blood Type Calculator

A person's common blood type combines the ABO group with the Rh factor. The ABO system has A, B, AB, and O phenotypes. A child receives one ABO allele from each biological parent. A and B are codominant, meaning both are expressed together as AB, while O is generally recessive. Someone with type A may carry either two A alleles or one A and one O allele. Type B has a similar uncertainty. Type AB carries one A and one B, and type O generally carries two O alleles. Because routine blood typing reports a phenotype rather than the hidden allele pair, some crosses have several possible outcomes. An A parent and an O parent, for example, can have an A or O child if the A parent carries O, but only A children if that parent carries two A alleles. This calculator includes all outcomes consistent with the selected phenotypes. It does not assume that each hidden genotype is equally common, so it deliberately reports possibilities rather than precise percentages. The Rh display is simplified to positive or negative. In the usual inheritance model, the positive trait is dominant and the negative trait is recessive. A positive person may carry two positive variants or one positive and one negative variant, while a negative person generally carries two negative variants. Therefore two negative parents are expected to have a negative child, while a positive parent can allow either result depending on the variants carried. Real blood-group genetics includes additional antigens and uncommon variants that a simple calculator cannot model. Blood types are medically important for transfusion and pregnancy care, but inheritance possibilities are not the same as transfusion compatibility. Red-cell donation rules depend on both ABO and Rh matching, antibodies, product type, and clinical testing. Pregnancy involving an Rh-negative pregnant person and an Rh-positive fetus also requires professional prenatal assessment; preventive treatment is routinely available in appropriate circumstances. Use this tool for education and family genetics exploration only. Blood type can sometimes exclude a proposed biological relationship, but it cannot prove parentage because many unrelated people share the same type and hidden genotypes remain unknown. DNA testing is the appropriate method for parentage questions. Laboratory typing, transfusion decisions, prenatal care, and interpretation of unusual results should always be handled by qualified professionals.