SwiftTools

Blood Type Calculator

Want to know what blood type your future baby might have? Enter the biological parents' blood types to reveal all genetically possible (and impossible) combinations.

MBiological Mother

FBiological Father

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How Blood Genetics Works

Human blood type is largely determined by two distinct genetic systems working at the same time: the ABO system and the Rh system. You inherit alleles (versions of genes) from both your biological mother and father.

Dominant vs Recessive Genes

In the ABO system, the A and B genes are dominant, while the O gene is recessive.

  • If you inherit an A gene from mom and an O gene from dad, your blood type will be A, because A overpowers O. We call this blood type A, but your genotype is actually AO.
  • Because O is recessive, the only way a person can have Type O blood is if they inherited an O gene from both parents (Genotype OO).
  • If you inherit an A gene from one parent and a B from the other, they share dominance. You will have Type AB blood.

Understanding the Rh Factor (+ or -)

The Rhesus (Rh) factor indicates the presence of a specific protein on the surface of your red blood cells. If you have it, you are Rh positive (+). If you lack it, you are Rh negative (-).

Genetically, positive (+) is a dominant trait, while negative (-) is recessive. Therefore:

  • Two Rh Negative parents will always have an Rh Negative child.
  • Two Rh Positive parents will usually have an Rh Positive child but can have an Rh Negative child if both happen to carry a hidden negative gene.

Frequently Asked Questions

How is a child's blood type determined?
A child's blood type is entirely genetic, inherited from both the biological mother and the biological father. Genes determine both the ABO group (A, B, AB, or O) and the Rhesus (Rh) factor (positive or negative).
Can a child have a different blood type than both parents?
Yes! Because parents carry both dominant and recessive alleles, it is very common. For example, if a mother is Type A (carrying an A and an O allele) and a father is Type B (carrying a B and an O allele), they could have a child with Type A, Type B, Type AB, or Type O blood.
How does the Rh factor (+ or -) work?
The Rh positive (+) gene is dominant over the Rh negative (-) gene. If both parents are Rh negative, their child MUST be Rh negative. If both parents are Rh positive, their child will likely be positive, but could still be negative if both parents carry a hidden recessive negative allele.
Are blood type calculators 100% accurate?
They are 100% scientifically accurate at telling you what is genetically possible or impossible via standard Mendelian inheritance. However, they cannot tell you exactly which one of the possibilities the child will actually have until they are born and tested.

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