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BloodTypeCalc.com

Parent Blood Type Calculator

Explore possible blood types for the other parent

Enter the child's blood type and one parent's blood type.

By BloodTypeCalc.com Editorial TeamPublished Suggest a correction
A family of three holding hands, framed by leaves
Child's blood type
Known parent

Find possible parent types

Results are based on standard inheritance of ABO and Rh factors. Rare genetic variations are not included.

FAQ

Common questions

How does the parent blood type calculator work?
It checks every genotype the known parent could have against every genotype a candidate parent could have. If any combination could produce the child's blood type under standard ABO and Rh inheritance, that candidate type is listed as possible.
Can blood type determine who the parent is?
No. Blood type can only exclude some possibilities under standard assumptions. It can never confirm a biological relationship. DNA testing is the only appropriate method for determining parentage.
What are the limitations of blood type testing?
It ignores rare variants such as Bombay phenotype, cis-AB, and weak D, and it depends on the entered blood types being correct. Because A, B, and Rh-positive types can hide a recessive allele, many combinations remain possible, so the tool answers 'could this type work?' rather than 'how likely is it?'

What this tool tells you

This is a possibility check. For each of the eight common blood types, it asks whether at least one standard genotype combination between that type and the known parent could produce the child's type. If yes, the type is listed as possible. If no, it is listed as excluded.

It does not rank possibilities, estimate a likelihood of parentage, or account for rare variants and laboratory error. A result that excludes a type is a reason to double-check the recorded blood types, not a conclusion about a relationship.

Example

A type O child with a type A known parent: the known parent must be AO (carrying an O allele), and the other parent must also carry an O allele. That means the other parent could be A, B, or O, but not AB, because AB people have no O allele to pass on.

Forward calculation

Know both parents' types?

Use the baby calculator to see every possible blood type for a child, with probabilities.

Open the baby calculator

Related reading

ABO inheritance explainedAlleles, genotypes, and Punnett squares.Rh factor explainedHow Rh-positive and Rh-negative are inherited.All blood typesReference pages for the eight common types.

Sources

Information on this page is paraphrased from the following authoritative sources.

  1. Blood typing(opens in a new tab)MedlinePlus, U.S. National Library of Medicine
  2. Facts About Blood and Blood Types(opens in a new tab)American Red Cross