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Baby blood type calculator

Choose the mother’s blood type and the father’s, and we will show which blood types their child can have, which the child cannot inherit, and the chance of each.

Reviewed against international medical sources · Last reviewed: 17 October 2026 · Sources

This tool gives general guidance based on published rules, which differ by country and change over time. It does not replace a medical assessment. The doctor at the donation centre always makes the final decision. In an emergency, call your local emergency number.

How does a child inherit a blood type?

Each trait is set by two genes, one from the mother and one from the father. The ABO blood groups have three versions of the gene: A, B and O. A and B are stronger than O, so someone with AO is type A, someone with BO is type B, and type O only appears in someone who inherited O from both parents. Type AB carries both A and B.

Blood type inheritance chart for parents and child

The ABO groups a child can have for every pair of parents’ groups. It does not matter which parent is which.

Parents’ groups Possible for the child Not expected in ordinary inheritance
O × O O ABAB
O × A OA BAB
O × B OB AAB
O × AB AB OAB
A × A OA BAB
A × B OABAB None
A × AB ABAB O
B × B OB AAB
B × AB ABAB O
AB × AB ABAB O

And how is Rh inherited?

The Rh factor (positive or negative) is another gene, independent of ABO. The positive gene (D) is stronger than the negative one (d). A positive parent may carry DD or Dd, while a negative parent always carries dd. When both parents are negative, the child is always negative.

Parents’ groups Possible for the child Not expected in ordinary inheritance
Rh+ × Rh+ Rh+Rh- None
Rh+ × Rh- Rh+Rh- None
Rh- × Rh- Rh- Rh+

The highlighted row is the pair of parents you entered. Rare genetic variants (such as the Bombay phenotype or cis-AB) can differ from this chart.

ABO and Rh blood type inheritance chart for children from both parents
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Quick rules

  • Two type O parents can only have a type O child.
  • Two type A parents can have an A or an O child, and cannot have a B or AB child.
  • If one parent is AB, the child cannot be type O.
  • If one parent is O and the other is AB, the child is A or B only.
  • Two Rh negative parents cannot have an Rh positive child.

Why does knowing the blood type matter?

Knowing your blood type helps in emergencies, when donating, and in pregnancy. See who your type can give to and receive from in the blood type compatibility chart. Blood type compatibility chart.

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Frequently asked questions

Can two type A parents have a type O child?

Yes, if both carry AO, the child inherits O from each with a 25% chance. They cannot have a B or AB child.

Can an A parent and a B parent have a type O child?

Yes, if the mother is AO and the father is BO, the chance of inheriting O from both is 25%. They can also have an A, B or AB child.

What is the rarest blood type?

AB negative is among the rarest. The rarer the type, the more each donor of that type matters.

Is this enough to know my child’s blood type?

No. These are predictions from inheritance. Your child’s actual blood type is found with a simple blood test by a doctor.

When is Rh checked in pregnancy?

Doctors usually ask for the mother’s blood type and Rh at the start of pregnancy. Ask your doctor about the right schedule for you.

Sources

This tool is based on the published guidelines below. Some rules differ between countries, and the donation centre in your country has the final word.

  1. Blood typing MedlinePlus (US National Library of Medicine)
  2. Rh incompatibility MedlinePlus (US National Library of Medicine)
  3. Blood Types Explained American Red Cross

Content and links last reviewed: 17 October 2026. How we write the tools

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