Can two A-type parents have an O-type child?

Yes, if both parents are heterozygous (I^A i). Each parent has a 50% chance of passing the recessive i allele, giving a 25% chance that the child inherits ii (type O).

Can two O-type parents have a non-O child?

No. Type O parents are always genotype ii. They can only donate i alleles, so every child must be ii (type O).

Why can AB parents never have an O child?

AB parents have genotype I^A I^B — they carry no recessive i allele. Every child receives either I^A or I^B, making type O (ii) impossible.

How is Rh factor probability calculated?

Rh+ individuals can be RR (homozygous) or Rr (heterozygous carrier). Rh- individuals are always rr. When both parents are Rh+, the tool considers both RR and Rr possibilities, so a 25% Rh- child probability can occur if both parents are Rr carriers.

What does the probability percentage mean?

It is the weighted average probability, across all genotype combinations consistent with each parent's phenotype, that a randomly conceived child will have that particular blood type.

Does this cover rare blood group systems?

No. Only the standard ABO and Rh(D) systems are modeled. Rare variants, weak-D expression, and other systems (Kell, Duffy, Kidd, MNS) are outside the scope of this tool.

What is the full reference matrix?

The reference matrix shows the most likely child blood type (by highest probability) for all 64 parent blood type combinations in a single table. Click any cell to load that parent pair instantly.

Blood Type Probability Calculator

Select both parents' blood types to see a probability breakdown of every blood type their child could inherit, with a full visual reference matrix.

Parent 1

Selected: —

Parent 2

Selected: —

Try an example:

Select both parents' blood types above to see child blood type probabilities.

Child Blood Type Probabilities

Percentages are averaged over all genotype combinations consistent with each parent's blood type.

Genotype Breakdown

Blood Type	ABO Genotypes	Rh Genotypes	Probability

Note: This tool models the standard ABO and Rh(D) systems only. Rare allelic variants, weak-D phenotypes, and other blood group systems (Kell, Duffy, Kidd, etc.) are not included. For clinical or paternity decisions, consult a certified laboratory.

Full Reference Matrix

Shows the most probable child blood type for all 64 parent combinations. Click any cell to load that pair above.

Summary

The Blood Type Probability Calculator applies Mendelian genetics to predict the likelihood of each possible child blood type given both parents' ABO and Rh(D) types. ABO is controlled by three codominant alleles (I^A, I^B, i), while Rh is a dominant/recessive pair (R dominant over r). Because a single phenotype can correspond to multiple genotypes — for example, type A can be I^A I^A or I^A i — the calculator enumerates every valid parental genotype pairing, runs a full Punnett cross, and averages the resulting offspring frequencies to compute an unbiased probability for each child blood type. All calculation runs entirely in your browser with no data sent to any server.

How it works

Select Parent 1's blood type by clicking an ABO type button (A, B, AB, or O) and an Rh button (+ or -).
Select Parent 2's blood type the same way.
The calculator lists every ABO genotype consistent with each parent's phenotype.
ABO and Rh alleles are crossed independently using Punnett square logic for all genotype combinations.
Offspring genotypes are converted to phenotypes (e.g., I^A i = type A), counted, and averaged across all parental pairings.
Results are shown as percentage probabilities for each possible child blood type, sorted from most to least likely.

Use cases

Estimate possible blood types for a future child based on parental blood types.
Understand why two type-A parents can have a type-O child (heterozygous carrier scenario).
Confirm that two O-type parents can only produce O-type children.
Learn why AB parents cannot have an O-type child.
Study Mendelian genetics principles with a real-world inheritance example.
Assist nursing and medical students reviewing ABO and Rh genetics.
Quickly check all 64 parent-pair scenarios using the full reference matrix.
Verify blood type incompatibility scenarios in genetics coursework.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu