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BloodTypeCalc.com

Baby Blood Type Calculator

What blood type could your baby have?

Enter both parents' ABO and Rh types to explore possible outcomes.

Two parents holding a newborn, with small ABO and Rh markers beside them
By BloodTypeCalc.com Editorial TeamPublished · Updated Suggest a correction

Enter both parents' blood types

Parent 1
Parent 2

Possible child blood types

Educational estimates only. A laboratory test is required to confirm blood type.

How it works

  1. 1. Enter parents' types

    Select each parent's ABO type and Rh factor.

  2. 2. We analyze inheritance

    The tool evaluates every possible genetic combination.

  3. 3. See possible outcomes

    View the blood types your baby could have, with probabilities.

Explore our other tools

This tool is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for medical concerns.

How blood type inheritance works

Your blood type is defined by two independent systems. The ABO system depends on which sugars sit on the surface of red blood cells: A antigen, B antigen, both (AB), or neither (O). The Rh system depends mainly on whether the RhD protein is present (Rh-positive) or absent (Rh-negative).

Each parent contributes one ABO allele and one Rh allele. A and B are co-dominant to each other and dominant over O; the D allele is dominant over d. That is why a type A person may carry a hidden O allele, and why two Rh-positive parents can have an Rh-negative child.

ABO type → possible genotypes

  • A → AA or AO
  • B → BB or BO
  • AB → AB
  • O → OO

Rh type → possible genotypes

  • Rh+ → DD or Dd
  • Rh− → dd

Read the complete ABO inheritance guide.

Example: type A parent and type O parent

If one parent is type A and the other is type O, the child will be type A or type O. If the A parent is AA, every child is type A. If the A parent is AO, each child has a 50% chance of A and 50% chance of O. Because we cannot tell AA from AO by blood type alone, the calculator reports type A as 50%–100% and type O as 0%–50%.

Type B and type AB are not expected in this pairing, because neither parent carries a B allele.

What this calculator can and cannot do

It can

  • Show which blood types are possible for a child under the standard ABO/Rh model
  • Give exact probabilities when the parents' genotypes are fully known
  • Give honest ranges when a parent could carry a hidden allele
  • Handle unknown parent inputs by showing every consistent outcome

It cannot

  • Determine or confirm anyone's actual blood type
  • Prove or disprove biological parentage
  • Account for rare variants such as Bombay phenotype, cis-AB, or weak D
  • Replace laboratory blood typing or advice from a healthcare professional

Reverse lookup

Know the child's type but not a parent's?

The parent calculator shows which blood types the other parent could have, given the child and one known parent.

Open the parent calculator

Frequently asked questions

Can two O parents have an A, B, or AB child?
Under the standard ABO model, no. Type O people carry two O alleles, so each passes an O allele to the child, and the child is type O. Very rare exceptions such as the Bombay phenotype exist, which is why laboratory testing is the only way to confirm a blood type.
Can two Rh-positive parents have an Rh-negative baby?
Yes. Rh-positive can be DD or Dd. If both parents are Dd, each has a 50% chance of passing the d allele, giving a 25% chance of an Rh-negative (dd) child.
Why does the calculator show a range like 0%–25%?
Because some blood types hide a second allele. A type A parent might be AA or AO; you can't tell from the phenotype alone. The calculator reports the minimum and maximum probability across every genotype combination that fits the parents' types.
Can this tell me whether someone is the biological parent?
No. Blood type can sometimes exclude a relationship under standard assumptions, but it can never confirm one. Only appropriate DNA testing can establish biological parentage.
Is my data stored?
No. All calculations run in your browser. Blood-type selections and results are never sent to our servers or included in analytics.

Keep learning

Blood type compatibility chartWho can donate to whom for red cells and plasma.Rh factor and pregnancyWhy Rh-negative status matters and how it is managed.All eight blood types explainedAntigens, antibodies, and inheritance for each type.

Sources

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

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