Question 1

How do I calculate my baby's blood type from parents?

Accepted Answer

Select both parents' ABO blood types (A, B, AB, or O) and Rh factors (positive or negative) in the calculator. It uses Punnett square genetics to show all possible child blood types with their probability percentages. For example, if one parent is Type A and the other is Type B, the child could be Type A, B, AB, or O depending on whether the parents carry recessive alleles.

Question 2

Can two parents with Type O blood have a child with a different blood type?

Accepted Answer

No. Two Type O parents can only have children with Type O blood. Type O is genotype 'ii' (two recessive alleles), so both parents can only pass the 'i' allele to their child, resulting in genotype 'ii' (Type O). This is one of the definitive rules of blood type inheritance.

Question 3

What is a Punnett square and how does it apply to blood types?

Accepted Answer

A Punnett square is a grid diagram used in genetics to predict the possible genotypes of offspring. For blood types, you list one parent's possible alleles along the top and the other parent's along the side, then fill in each cell with the combined genotype. Since ABO has three alleles (A, B, O) with codominance between A and B, and dominance over O, the Punnett square helps visualize all possible combinations and their resulting blood types.

Question 4

Can blood type be used for a paternity test?

Accepted Answer

Blood type can exclude a potential father but cannot confirm paternity. For example, if both parents are Type O (genotype ii), the child must also be Type O. If the child is Type A or B, the stated father is excluded. Similarly, a Type AB father cannot have a Type O child, since he must pass either an A or B allele. However, blood type exclusion is limited — many combinations are compatible with multiple potential fathers. DNA testing is the standard method for confirming biological parentage.

Question 5

What is the Rh factor and why does it matter?

Accepted Answer

The Rh factor is a protein (D antigen) on the surface of red blood cells. Rh-positive (Rh+) means the protein is present, and Rh-negative (Rh-) means it's absent. The D allele is dominant, so a person needs only one D allele to be Rh+. It matters especially during pregnancy: if an Rh-negative mother carries an Rh-positive baby, her body may produce antibodies against the baby's blood cells (Rh incompatibility), which can be managed with RhIg (RhoGAM) injections.

Question 6

What is the rarest blood type?

Accepted Answer

AB-negative is the rarest blood type, found in less than 1% of the global population. In the United States, approximately 1% of people have AB- blood. The most common blood type worldwide is O-positive, found in about 39% of people globally.

Question 7

Can two Rh-positive parents have an Rh-negative child?

Accepted Answer

Yes. If both parents are heterozygous Rh-positive (genotype Dd), each has a 50% chance of passing the recessive 'd' allele. There's a 25% chance their child will be dd (Rh-negative). This calculator accounts for this by showing the probability breakdown when both parents are Rh+.

Question 8

What does universal donor and universal recipient mean?

Accepted Answer

Type O-negative is called the 'universal donor' because O- red blood cells lack A, B, and D antigens, making them safe to transfuse to almost anyone in emergencies. Type AB-positive is the 'universal recipient' because AB+ individuals have A, B, and D antigens on their cells and no anti-A, anti-B, or anti-D antibodies, so they can receive red blood cells from any blood type.

Question 9

Why does this calculator show probability ranges instead of a definitive blood type?

Accepted Answer

Because blood type phenotype (what you observe) doesn't reveal the full genotype. A person with Type A blood could be genotype AA (homozygous) or AO (heterozygous). Without genetic testing, we can't know which. This calculator considers all possible genotype combinations equally likely and calculates the weighted probability of each possible child blood type.

P1 ↓ / P2 →	B	B
A	AB(AB)	AB(AB)
A	AB(AB)	AB(AB)

P1 ↓ / P2 →	B	O
A	AB(AB)	AO(A)
A	AB(AB)	AO(A)

P1 ↓ / P2 →	B	B
A	AB(AB)	AB(AB)
O	BO(B)	BO(B)

P1 ↓ / P2 →	B	O
A	AB(AB)	AO(A)
O	BO(B)	OO(O)

P1 ↓ / P2 →	D	D
D	DD(+)	DD(+)
D	DD(+)	DD(+)

Blood Type Calculator

Probability Breakdown

Genotype Probabilities

Punnett Squares

Transfusion Compatibility

How Blood Type Inheritance Works

Punnett Square for Blood Types

Blood Type Distribution Worldwide

Blood Type Compatibility for Transfusions

Frequently Asked Questions

Embed Blood Type Calculator

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Type	Chance	Donates To	Receives From
AB+	53%	AB+	O-O+A-A+B-B+AB-AB+
A+	18%	A+AB+	O-O+A-A+
B+	18%	B+AB+	O-O+B-B+
O+	5.9%	O+A+B+AB+	O-O+
AB-	3.5%	AB-AB+	O-A-B-AB-
A-	1.2%	A-A+AB-AB+	O-A-
B-	1.2%	B-B+AB-AB+	O-B-
O-	<1%	O-O+A-A+B-B+AB-AB+	O-

P1 ↓ / P2 →	D	d
D	DD(+)	Dd(+)
d	Dd(+)	dd(-)