GeneCalc

Blood Type Calculator

Punnett square genetics — which blood types are possible (and impossible) for your child.

Parent 1 type

Parent 1 Rh

Parent 2 type

Parent 2 Rh

Possible child blood types

AB+, AB-, A+, A-, B+, B-, O+, O-

What you entered

Parent 1: A+Parent 2: B+

1
Parent 1 possible alleles (A+)
AA or AO= Type A
2
Parent 2 possible alleles (B+)
BB or BO= Type B
3
Possible ABO outcomes (Punnett square)
Cross all allele combinations= AB, A, B, O
4
Possible Rh outcomes
+ × += Rh+, Rh-
5
Possible child blood types
ABO × Rh combinations= AB+, AB-, A+, A-, B+, B-, O+, O-

Result

Possible types: AB+, AB-, A+, A-, B+, B-, O+, O-

Parents with blood types A+ and B+ can have children with blood types: AB+, AB-, A+, A-, B+, B-, O+, O-.

Possible child blood types by parents' types

A and B are co-dominant and O is recessive, so two parents can produce a type neither of them has. Rh positive is dominant over Rh negative.

Parent 1	Parent 2	Possible child types	Impossible
A+	O+	A+, A-, O+, O-	B and AB
A+	B+	Any type	None
O-	O-	O- only	A, B, AB, and any Rh+
AB+	O+	A+, A-, B+, B-	AB and O
B+	B-	B+, B-, O+, O-	A and AB
AB+	AB+	A+, A-, AB+, AB-, B+, B-	O

Two type A parents can have a type O child if both carry a recessive O allele, and two AB parents can never have a type O child. Rare exceptions such as the Bombay phenotype fall outside this model, so never use it to draw conclusions about parentage. General wellness information only, not medical advice. Discuss any health decision with a qualified clinician.

ABO blood type genetics

Blood type is determined by two alleles inherited from your parents. A and B are codominant (both expressed if present), while O is recessive (only expressed when paired with another O). This is why two type-A parents can have a type-O child — both may carry a hidden O allele.

The Rh factor adds another layer

The + or − in your blood type refers to the Rh(D) antigen. Rh+ is dominant — two Rh+ parents can have an Rh− child if both carry the recessive allele, but two Rh− parents cannot have an Rh+ child. This has important implications for pregnancy (Rh incompatibility).

Frequently asked questions

Can two parents with type A blood have a type O child?

Yes — if both parents carry a hidden O allele (genotype AO). Each parent has a 50% chance of passing the O allele, so there's a 25% chance the child is OO (type O). If either parent is AA (homozygous), all children will be type A. You can't tell AA from AO just from a standard blood test.

What is the rarest blood type?

AB negative is the rarest (< 1% of population). O positive is the most common (~37%). Distribution varies by ethnicity: type B is more common in Asian populations, type O in Indigenous American populations. The full rarity order (US): O+ (37%), A+ (36%), B+ (9%), O− (7%), A− (6%), AB+ (3%), B− (2%), AB− (<1%).

What is Rh incompatibility in pregnancy?

If an Rh− mother carries an Rh+ baby, her immune system may produce antibodies against Rh+ blood cells. This rarely affects a first pregnancy but can cause hemolytic disease in subsequent Rh+ pregnancies. Prevention: an RhoGAM injection at 28 weeks and after delivery. All Rh− mothers should discuss this with their doctor.