Find out which blood types a child can inherit. Choose the mother's and father's ABO group and Rh factor to see every possible blood type with its probability, the Punnett squares behind it, and which types are impossible.
Last updated:
Unknown genotypes
A person with type A can be AA or AO; this choice sets how likely each is.
Enter your values to see the result.
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How to use the Blood Type Calculator
Choose the mother's blood type, for example A+.
Choose the father's blood type.
Pick how to weight unknown genotypes: realistic population frequencies, or every possible genotype equally likely.
Press Calculate blood types to see possible types, probabilities and impossible types.
Study the Punnett squares and the genotype table to see where each result comes from.
ABO blood type inheritance chart
Parents
Possible child ABO groups
Not possible
O × O
O
A, B, AB
O × A
O, A
B, AB
O × B
O, B
A, AB
O × AB
A, B
O, AB
A × A
A, O
B, AB
A × B
A, B, AB, O
none
A × AB
A, B, AB
O
B × B
B, O
A, AB
B × AB
A, B, AB
O
AB × AB
A, B, AB
O
Rh factor inheritance
Parents
Possible child Rh
Rh+ × Rh+
Rh+ or Rh− (Rh− only if both carry d)
Rh+ × Rh−
Rh+ or Rh− (Rh− only if the positive parent carries d)
Rh− × Rh−
Rh− only
The full blood type combines both genes, which are inherited independently: P(child is A−) = P(A) × P(Rh−). Blood typing for medical purposes must always be done by a laboratory.
Frequently asked questions
How is blood type inherited?
Each parent passes one ABO allele (A, B or O) and one Rh allele (D for positive, d for negative). A and B are co-dominant and both dominate O, so AO is type A, BO is type B, AB is type AB and only OO is type O. Rh-positive is dominant, so only dd is Rh-negative.
Can two O parents have an A or B child?
Not under standard ABO inheritance: two type O parents (OO × OO) can only pass on O alleles, so their children are type O. Very rare exceptions exist, such as the Bombay phenotype and cis-AB, which is why a blood type mismatch is never proof on its own about parentage.
Can two Rh-positive parents have an Rh-negative baby?
Yes. If both parents carry a hidden negative allele (Dd), each child has a 1 in 4 chance of being dd, which is Rh-negative.
Why are the percentages different from other charts?
Many charts only list which types are possible. To give probabilities you must guess each parent's hidden genotype, for example whether a type A parent is AA or AO. This calculator either weights those by approximate population allele frequencies (A 22%, B 16%, O 62%, Rh-negative 39%) or treats them as equally likely; you can switch between the two.
What is Rh incompatibility?
If an Rh-negative mother carries an Rh-positive baby, her immune system can make antibodies that affect a later Rh-positive pregnancy. It is routinely checked during prenatal care and prevented with anti-D immunoglobulin, so talk to your doctor or midwife.
What blood types can A+ and B+ parents have?
Any of the 8 types: AB, A, B or O, each positive or negative, because both parents may carry hidden O and Rh-negative alleles. AB+ is the single most likely result.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.