Blood type inheritance chart
Each pair of ABO types has its own page below, with every Punnett square, the chance of each child type on US and England blood group figures, the Rh factor and the rare exceptions.
Which blood types can a child inherit from each pair of parents?
A child gets one ABO allele from each parent, so the parents’ types set the limits. Two type O parents have only type O children, an AB and an O parent only type A or B, and type A and type B parents can have any of the four. The chart below gives every pair, with the likeliest type.
Every pair of parents
| Parents | Possible | Not possible | Likeliest, US | Likeliest, England |
|---|---|---|---|---|
| A and A parents | A and O | B and AB | A, 82.6% | A, 81.2% |
| A and B parents | A, B, AB and O | none | AB, 30.7% | AB, 29.7% |
| A and AB parents | A, B and AB | O | A, 50% | A, 50% |
| A and O parents | A and O | B and AB | A, 58.3% | A, 56.7% |
| B and B parents | B and O | A and AB | B, 77.5% | B, 77.4% |
| B and AB parents | A, B and AB | O | B, 50% | B, 50% |
| B and O parents | B and O | A and AB | B, 52.6% | B, 52.4% |
| AB and AB parents | A, B and AB | O | AB, 50% | AB, 50% |
| AB and O parents | A and B | AB and O | A or B, 50% each | A or B, 50% each |
| O and O parents | O | A, B and AB | O, 100% | O, 100% |
By ordinary inheritance. Each pair’s page gives the rare exceptions, such as the Bombay phenotype and cis-AB, with every Punnett square behind its figures.
How the chances are worked out
A blood type does not give the genotype: type A is AA or AO, and type B is BB or BO. The calculator weighs each by Hardy-Weinberg proportions, which need the allele frequencies of a population. Blood services publish the share of each type instead, so the frequencies come from Bernstein’s method: r = √O, p = 1 − √(O + B) and q = 1 − √(O + A), adjusted so the three add to 1, and d is the square root of the Rh negative share.
| Quantity | US | England |
|---|---|---|
| Type O, published share | 44% | 50% |
| Type A, published share | 42% | 36% |
| Type B, published share | 10% | 11% |
| Type AB, published share | 4% | 3% |
| Rh negative, published share | 15% | 26% |
| Allele A frequency, p | 0.265 | 0.219 |
| Allele B frequency, q | 0.0726 | 0.0727 |
| Allele O frequency, r | 0.662 | 0.708 |
| Allele d frequency | 0.387 | 0.510 |
| Type A person who is AO | 83.3% | 86.6% |
| Type B person who is BO | 94.8% | 95.1% |
| Rh positive person who is Dd | 55.8% | 67.5% |
US figures: Stanford Blood Center’s estimates for the US population (“Blood Types”, read October 9, 2026; general estimates for teaching, taken from the AABB Technical Manual, 18th edition). England figures: NHS Blood and Transplant’s shares of donors in England (“Blood types”, read October 9, 2026; accurate at February 2026 and rounded to whole numbers).
The values are facts and free to use; this table’s selection and presentation are © 2026 ScienceQuest.
Both are national figures, not broken down by ancestry, and England’s are blood donors rather than the whole population, so treat every percentage as an estimate. Known genotypes or grandparents’ types give firmer answers, and the calculator takes both.
Rh factor
Rh is inherited separately from ABO. Two Rh positive parents have an Rh negative child 7.79% of the time on US figures and 11.4% on England’s, an Rh positive and an Rh negative parent 27.9% and 33.8%, and two Rh negative parents only Rh negative children, by ordinary inheritance.
Work out your own family
The blood type calculator takes both parents’ full types, Rh included, with grandparents’ types or a known genotype, and draws the weighted square. The Punnett square calculator crosses any genotypes, and the Hardy-Weinberg calculator shows where genotype frequencies come from.