If you’ve ever wondered what blood type really means or what blood type your baby might have, this blood type calculator is the simplest way to find out. By entering the parents’ blood groups, you can instantly see all possible blood types for your child.

In this guide, you’ll also find an easy-to-read table explaining how different blood groups affect blood transfusion compatibility between donors and recipients.

Expecting a baby? You might also find our pregnancy weight gain calculator helpful.

We strive to make all Omni Calculators accurate and reliable, but please note that this tool cannot replace professional medical advice or diagnosis.

What Determines Your Blood Type?

There are four major blood groups: A, B, AB, and O. Each group is defined by specific antigens located on the surface of your red blood cells. These antigens—and the antibodies in your blood plasma—determine your blood type.

Your blood type is inherited genetically. Each person receives two alleles, one from each parent, for the blood-group gene:

• Type A: AA or AO

• Type B: BB or BO

• Type AB: AB

• Type O: OO

Alleles A and B are dominant; O is recessive. This means only people with OO alleles will have type O blood.

The calculator also includes the Rh system, which identifies blood as Rh+ or Rh-, depending on whether the Rh(D) antigen is present. The negative Rh allele is recessive, so two Rh- parents will always have Rh- children.

💡 Rh- mothers often require immunoglobulins to prevent hemolytic disease in the fetus or newborn. For dosing information, see our IVIG calculator.

What Blood Type Will My Baby Have?

Your child inherits one allele from each parent. For example, if your blood type is A and your partner’s is AB, here’s what happens:

1. Your blood type A can genetically be AA or AO.

2. You can pass down either A (75%) or O (25%).

3. Your partner with type AB passes down A (50%) or B (50%).

By combining the possibilities, your child’s potential genotypes and blood types are:

• AA: 37.5%

• AB: 37.5%

• AO: 12.5%

• BO: 12.5%

So the predicted blood types are:

• A: 50%

• B: 12.5%

• AB: 37.5%

For Rh factor:

• Both Rh+: 93.75% Rh+, 6.25% Rh-

• Both Rh-: 100% Rh-

• One Rh+, one Rh-: 75% Rh+, 25% Rh-

Of course, the calculator does all of this instantly for you—no manual math needed 😊.

Blood Transfusion Compatibility

Because of the antigen–antibody system, not all blood types are compatible. Our blood donor calculator can help you determine safe donor–recipient pairings, but here are the basic rules:

• AB: Universal recipient, but can donate only to AB.

• A or B: Can receive from the same type or O; can donate to their type and AB.

• O: Universal donor but can receive only O.

• Rh+: Can donate only to Rh+, but can receive Rh+ or Rh-.

• Rh-: Can donate to both Rh+ and Rh- but can receive only Rh-.

A full compatibility table is included below for easy reference.

Can a Child Have a Different Blood Type Than Both Parents?

Yes. For example, parents with AB+ and O+ blood types can have children with either A or B, but usually not AB or O.

What Are the Rarest Blood Types?

Some of the rarest blood groups include B-, AB+, and AB-. Here’s how common each blood type is in the population:

FAQs

What blood type will a child have if both parents are B+?

The child may be B or O, and most likely Rh+. If both parents carry the Rh- allele, the child may also be Rh-.

Which blood type can donate to everyone?

O- is the universal donor. It has no antigens that could trigger a reaction in other blood types.

Can two B-type parents have a child with O blood?

Yes—if both parents carry the BO genotype.

How do I determine my child’s possible blood types?

1. Write down both parents’ blood types.

2. Identify possible genotypes (AA/AO, BB/BO, AB, or OO).

3. Combine one allele from each parent.

4. Convert the genotype combinations into blood types.