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

Yes. Blood type A can be genotype I^A I^A (homozygous) or I^A i (heterozygous carrier). If both parents are I^A i, each parent can pass on the recessive i allele, giving a 25% chance of an ii (type O) child.

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

No. Type O parents are always genotype ii. They can only pass i alleles to their children, so all children will be ii (type O).

Why can AB parents not have an O child?

AB parents carry one I^A and one I^B allele — they have no recessive i allele to pass on. Every child must receive either I^A or I^B, so type O (ii) is impossible.

How does Rh factor inheritance work?

The Rh factor is controlled by a single gene with a dominant allele (Rh+, written R) and a recessive allele (Rh-, written r). Rh+ individuals may be RR or Rr. Rh- individuals are always rr. Two Rh+ parents who are both carriers (Rr) have a 25% chance of an Rh- child.

What does "probability" mean in the results?

The probability shown is the percentage chance that a randomly conceived child will have that blood type, averaged across all possible parental genotype combinations consistent with the selected blood types.

Does this tool cover rare blood type variants or subgroups?

No. The tool models the standard ABO and Rh(D) system only. Rare variants, weak D, and other blood group systems (Kell, Duffy, Kidd, etc.) are not included.

Is it possible to determine a child's exact blood type in advance?

Not always. Unless both parents are genotypically confirmed (e.g., via genetic testing), multiple genotypes may be consistent with a given blood type. The calculator shows all possibilities and their likelihoods.

Blood Type Inheritance Calculator

Select both parents' ABO and Rh blood types to see every possible blood type their children can inherit, with probabilities.

Select Parents' Blood Types

Parent 1

ABO type

Rh factor

Selected: —

Parent 2

ABO type

Rh factor

Selected: —

Examples:

Select both parents' blood types on the left to see possible child blood types.

Possible Child Blood Types

Genotype Breakdown

Blood Type	ABO Genotypes	Rh Genotypes	Probability

Note: Probabilities are calculated by averaging over all possible genotype combinations consistent with each parent's blood type (accounting for both homozygous and heterozygous possibilities). This tool models the standard ABO and Rh(D) system only.

Summary

The Blood Type Inheritance Calculator uses Mendelian genetics to predict which ABO and Rh blood types a child can inherit from their parents. ABO blood type is controlled by three alleles (I^A, I^B, and i), while the Rh factor is determined by a dominant/recessive allele pair (Rh+ dominant over Rh-). Because both parents may carry hidden recessive alleles, the tool evaluates all possible parental genotype combinations and calculates the probability of each child blood type. All computation runs entirely in your browser — no data is sent to any server.

How it works

Select Parent 1's ABO blood type (A, B, AB, or O) and Rh factor (+ or -).
Select Parent 2's ABO blood type and Rh factor.
The tool enumerates all possible parental genotype combinations for each parent's blood type.
ABO and Rh alleles are crossed independently using Punnett square logic.
Resulting child genotypes are converted to blood type phenotypes (e.g., I^A I^B = AB).
Probabilities are averaged across all parental genotype combinations and displayed as a percentage for each possible child blood type.

Use cases

Predict possible blood types for a future child based on parents' blood types.
Understand why two O-type parents always have O-type children.
Determine whether an AB+ child is possible from specific parent combinations.
Learn Mendelian inheritance in a real-world, relatable context.
Assist medical students studying ABO genetics and Rh factor inheritance.
Explore how carrier status (e.g., A with hidden recessive i) affects offspring probabilities.
Check compatibility in genetics coursework or exam scenarios.

Frequently Asked Questions

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