Blood Type Inheritance Calculator | Probability of Each Blood Type for a Child from the Parents' Blood Types, Impossible Types, AO and BO Genotypes, Narrowing Down with Grandparents, Rh Negative Inheritance, the Other Parent's Blood Type from a Child and One Parent, and a Combination Chart
The Blood Type Inheritance Calculator answers questions like “Can parents with type A and type B have a type O child?” and “What blood type could the parents of a type O child be?” using Mendel's laws. Choose each parent's blood type (A, B, O, AB or unknown) to see the probability of each blood type for their child as a percentage, along with the types this couple cannot have. Two type A parents can be AA or AO, which changes the outcome, so the calculator estimates each parent's genotype from the blood type distribution of the population you choose (the United States, Japan, South Korea or China). If you know a genotype you can pick AA, AO, BB, BO or OO directly, and entering the grandparents' blood types narrows it down, for example “the maternal grandfather is type O, so the mother must be AO”. Rh positive and negative are included too, with the chance of an Rh negative child from two Rh positive parents and combined results such as A Rh+. Each possible genotype combination is shown as a 2×2 Punnett square. You can also work backwards from a child and one parent to the other parent's possible and impossible blood types. Charts list the child's blood types for all 10 parent combinations and all 21 genotype combinations, with notes on rare exceptions such as cis-AB and the Bombay phenotype.
Parents' blood types
Get the probability of each blood type for the child from the parents' blood types. Knowing the grandparents' blood types or a genotype narrows down the parents' genotypes.
Father
Blood type (ABO)
Rh
Estimated genotype: AO 84.2% · AA 15.8%
Rh: Dd 47.5% · DD 37.5% · dd 15%
Mother
Blood type (ABO)
Rh
Estimated genotype: BO 94.5% · BB 5.5%
Rh: Dd 47.5% · DD 37.5% · dd 15%
Blood type distribution (used to estimate genotypes)
A 40%, B 11%, O 45%, AB 3.9%, Rh− 15%
The child's blood type
The child could be type A, B, O or AB.
Rh
Child's genotype: AB 30.5% · AO 27.4% · BO 22.2% · OO 19.9%
Genotype combinations
Even with the same blood types, the child's type depends on the genotypes (AA or AO, for example). These are the possible combinations and how likely each is.
Father AO × Mother BO79.6%
| F \ M | B | O |
|---|---|---|
| A | AB | AO |
| O | BO | OO |
Type A 1/4 · Type B 1/4 · Type O 1/4 · Type AB 1/4
Father AA × Mother BO14.9%
| F \ M | B | O |
|---|---|---|
| A | AB | AO |
| A | AB | AO |
Type A 1/2 · Type AB 1/2
Father AO × Mother BB4.6%
| F \ M | B | B |
|---|---|---|
| A | AB | AB |
| O | BO | BO |
Type B 1/2 · Type AB 1/2
Father AA × Mother BB0.9%
| F \ M | B | B |
|---|---|---|
| A | AB | AB |
| A | AB | AB |
Type AB 1
ABOUT
About Blood Type Inheritance Calculator | Probability of Each Blood Type for a Child from the Parents' Blood Types, Impossible Types, AO and BO Genotypes, Narrowing Down with Grandparents, Rh Negative Inheritance, the Other Parent's Blood Type from a Child and One Parent, and a Combination Chart
The Blood Type Inheritance Calculator works out the chance of a child being type A, B, O or AB from the parents' blood types, and which types are impossible. It also estimates AO and BO genotypes, narrows them down with the grandparents' blood types, covers Rh positive and negative, works backwards from a child and one parent to the other parent, and charts every combination.
How to use Blood Type Inheritance Calculator | Probability of Each Blood Type for a Child from the Parents' Blood Types, Impossible Types, AO and BO Genotypes, Narrowing Down with Grandparents, Rh Negative Inheritance, the Other Parent's Blood Type from a Child and One Parent, and a Combination Chart
- 1Under “Child's blood type from parents”, choose the father's and mother's blood types. Choose “Unknown” if you don't know one
- 2If you know a genotype (AO, BO and so on), use the genotype link to pick it. If you know the grandparents' blood types, add them with “Narrow down with the grandparents' blood types”
- 3If you know the Rh types, choose Rh+ or Rh−
- 4Read the probability of each blood type for the child, the types that cannot occur, and the table of possible genotype combinations
- 5To work out a parent from a child, open “Parent's blood type from a child” and choose the child's and the known parent's blood types
Great for
- Find the chance of each blood type for the child of a type A and a type B parent
- Talk with your family about what blood type your baby might be before the birth
- Check which blood types are possible and impossible for the parents of a type O child
- Use your parents' blood types to narrow down whether you are AO or AA
- Find the chance of an Rh negative child from two Rh positive parents
- Check Mendel's laws and blood type inheritance with Punnett squares in a biology class
- See all 10 parent combinations and the child's blood types in one chart
Good to know
- Blood type is set by three gene variants, A, B and O, and you inherit one from each parent. A and B are dominant over O, and A and B are codominant, so AA and AO are type A, BB and BO are type B, OO is type O and AB is type AB.
- When only a parent's blood type is known, you can't tell whether they are AA or AO. The calculator uses the blood type distribution of the population you choose to get gene frequencies (Hardy–Weinberg) and estimates the genotype from them. With US figures, about 16% of type A people are AA and 84% AO; with Japanese figures about 20% are AA.
- Entering the grandparents' blood types narrows down a parent's genotype. If either parent of a type A mother is type O, she must have inherited an O, so she is AO.
- For Rh, D (Rh+) is dominant over d (Rh−), so only dd is Rh negative. Two Rh positive parents who are both Dd have a 1 in 4 chance of an Rh negative child. About 15% of people in the US are Rh negative, compared with about 0.5% in Japan.
- ABO and Rh are separate genes, so the probabilities are multiplied to give combined results such as A Rh+.
- Rare exceptions are not included: cis-AB (an AB and an O parent can have an AB or O child), the Bombay phenotype (carries A or B genes but tests as type O) and weak subtypes.
- Blood type alone cannot establish or rule out parentage. If a result doesn't match, a sample mix-up or an unclear test as a newborn are also possible.
- Your entries are saved only in this browser and are never sent to a server.
Questions this tool answers
Use Blood Type Inheritance Calculator | Probability of Each Blood Type for a Child from the Parents' Blood Types, Impossible Types, AO and BO Genotypes, Narrowing Down with Grandparents, Rh Negative Inheritance, the Other Parent's Blood Type from a Child and One Parent, and a Combination Chart for searches like these:
- Find my child's possible blood types from the parents' blood types
- Find which blood types this couple cannot have
- Work out a parent's blood type from the child's
- Estimate whether a type A or B person is AA or AO
- Narrow down a parent's genotype with the grandparents' blood types
- Find the chance of an Rh negative baby
- See a chart of blood type combinations
FAQ
- What blood type will the child of a type A and a type B parent be?
- Any of A, B, O or AB is possible. Estimating the genotypes from US blood type figures, the chances are roughly AB 31%, A 27%, B 22% and O 20%. If the parents are AO and BO, each of the four types has a 1 in 4 chance; if they are AA and BB, the child is always AB.
- Can two type A parents have a type O child?
- Yes. If both parents are AO, there is a 1 in 4 chance of OO (type O). Using US blood type figures, the chance of a type O child from two type A parents is about 18%. Two type B parents can also have a type O child.
- Can an AB parent and an O parent have an AB or O child?
- Not with ordinary inheritance: the child is type A or type B, half and half. However, a parent with the rare cis-AB type, where A and B sit on the same gene, can have an AB or O child.
- What blood types can the parents of a type O child be?
- A type O child inherits an O from each parent, so each parent must be type A (AO), type B (BO) or type O. An AB parent cannot have a type O child, apart from rare exceptions such as cis-AB. If one parent is type A, the other parent is most likely type O, using US figures about 67%.
- How can I find out whether I am AA or AO?
- A standard blood test only shows type A; telling AA from AO needs a genetic test. However, if either of your parents or any of your children is type O, you must be AO. In this calculator, entering your parents' blood types as the grandparents narrows down the estimate.
- Can two Rh positive parents have an Rh negative child?
- Yes. If both parents are Dd (Rh positive but carrying the Rh negative gene), there is a 1 in 4 chance of an Rh negative child. Using US figures the chance for two Rh positive parents is about 7.8%, and about 28% if one parent is Rh negative.
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