Blood Type Calculator (Parent to Child)

Pick both parents' ABO group and Rh factor to see which blood types their child could have, with Punnett squares and estimated odds.

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Results will appear here once you enter your values.

How blood type is inherited

Your ABO blood group comes from one gene with three common versions (alleles): A, B and O. You carry two copies, one from each parent. A and B are both dominant over O, and A and B together are codominant, so they show up side by side as type AB.

  • Type A can be AA or AO.
  • Type B can be BB or BO.
  • Type AB is always AB.
  • Type O is always OO.

The Rh factor works the same way with a dominant D allele (Rh positive) and a recessive d (Rh negative). Rh-positive people are DD or Dd; Rh-negative people are dd.

Each parent passes on one allele at random, which is what a Punnett square lays out. For an AO parent and a BO parent, the four equally likely combinations are AB, AO, BO and OO, so that couple could have a child of any ABO type.

Reading the results and the odds

A blood type alone doesn't tell you a person's genotype: a type A parent might be AA or AO. The calculator therefore lists every child type that is possible for some combination of the parents' genotypes, and marks the rest as not expected.

The percentages go one step further and assume each genotype that fits a parent's blood type is equally likely. Real odds shift with family history and population: in many populations most type A people are AO, which makes a type O child more likely than an even split would suggest. Treat the percentages as illustrations, and the possible/not possible column as the reliable part.

Useful patterns:

  • Two type O parents normally have only type O children.
  • An AB parent and an O parent have A or B children, never AB or O.
  • Two Rh-negative parents normally have only Rh-negative children.
  • Two Rh-positive parents can have an Rh-negative child if both carry d.

Exceptions and what blood type can't tell you

  • Blood type is not a paternity test. Many unrelated people share a blood type, and rare variants can break the usual rules. Parentage questions need DNA testing.
  • cis-AB. A rare allele carries both A and B activity on one chromosome, so an AB parent can have an AB child with an O partner.
  • Bombay phenotype. People who lack the H antigen test as type O even when they carry A or B alleles, and can pass those alleles on.
  • Weak and partial D. Some Rh variants type differently depending on the test used.
  • Pregnancy. If a mother is Rh negative, her care team checks for Rh incompatibility with lab tests; this chart is not a substitute.

The ABO and Rh systems are described in detail in the NCBI Bookshelf reference Blood Groups and Red Cell Antigens.

Frequently Asked Questions

Common questions about the Blood Type Calculator (Parent to Child)

Normally no. Two type O parents both carry OO and can only pass on O. Very rare exceptions such as the Bombay phenotype can cause a parent to test as O while carrying A or B.

Sources & References

The ABO blood group. In: Dean L. Blood Groups and Red Cell Antigens. NCBI Bookshelf

ABO alleles, dominance, codominance of A and B, and rare variants such as cis-AB and the Bombay phenotype.
→Source: National Center for Biotechnology Information (NIH)

The Rh blood group. In: Dean L. Blood Groups and Red Cell Antigens. NCBI Bookshelf

Rh (D) inheritance and weak/partial D variants.
→Source: National Center for Biotechnology Information (NIH)

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