Child Blood Type Probability Calculator
Pick the known blood types of two parents to estimate possible child blood types (ABO + Rh).
This tool provides genetics-based probabilities, not certainties for any one child.
How this blood type calculator works
This calculator estimates the possible blood types of a child based on the blood types of two parents. It combines both major systems:
- ABO group (A, B, AB, or O)
- Rh factor (positive “+” or negative “-”)
You enter each parent’s known blood type, and the calculator generates probability estimates for the child’s blood type outcomes, such as A+, O-, AB+, and others.
Quick genetics refresher: ABO system
ABO blood type is controlled by two inherited alleles, one from each parent. The most common allele combinations are:
- A type: AA or AO
- B type: BB or BO
- AB type: AB
- O type: OO
A and B are dominant over O. That means a person with AO appears as type A, and a person with BO appears as type B. Type O appears only with OO.
Rh factor basics
Rh factor is usually simplified into positive or negative. A positive Rh can come from ++ or +- genotypes, while negative Rh is --. Since + is dominant, having at least one + allele generally gives Rh positive blood.
What the result percentages mean
The percentages represent a model-based probability across possible parental genotype combinations for the selected phenotypes. In plain language: they show what is possible and how likely each outcome is in theory, not a guaranteed prediction for a specific family.
- 0% means that blood type is not genetically possible in this model.
- Higher percentages mean that outcome is more likely.
- Real-world population genetics can shift exact odds.
Example scenarios
Example 1: O- and O-
If both parents are O-, the child will be O- in standard inheritance modeling because both parents can only pass O and Rh negative alleles.
Example 2: AB+ and O-
This pairing can produce A or B blood groups (but not AB or O in basic ABO inheritance), and Rh may be positive or negative depending on Rh alleles.
Important limitations
- This is an educational calculator and does not replace medical testing.
- Rare genetic variants (for example, weak D or unusual antigen expression) are not modeled here.
- For clinical decisions (pregnancy, transfusion, diagnosis), always rely on laboratory blood typing and professional guidance.
Why people use a blood type calculator
A blood type calculator is useful for classroom learning, family curiosity, and understanding inheritance patterns. It can also help explain why certain blood types are impossible or highly likely in parent-child combinations.
If you are trying to confirm identity, paternity, or medical compatibility, formal testing is essential. Blood type alone is never a complete identifier.