Blood Type Inheritance Calculator
Blood type inheritance calculator — choose both parents’ ABO group and Rh factor to see every blood type their child can have, and which are genetically impossible, based on standard ABO and Rh inheritance. An educational genetics tool. Runs in your browser.
Blood Type Inheritance Calculator
Parent 1
Parent 2
How to Use the Blood Type Calculator
Set parent 1
Choose the first parent’s ABO group and Rh factor.
Set parent 2
Choose the second parent’s ABO group and Rh factor.
See possible types
The grid highlights every blood type the child could have.
Note the impossible
See which ABO types are ruled out for this couple.
How Blood Type Passes Down
Few pieces of biology are as satisfyingly logical as blood type inheritance, which is why it appears in almost every school genetics class. Your blood group is governed by two independent systems. The ABO system rests on three alleles — A, B and O — of which A and B are co-dominant and O is recessive; each parent passes one allele, and the pair a child inherits fixes their group. The Rh system is simpler still: positive is dominant, so a person is Rh-negative only if they carry two negative alleles. This calculator works both systems at once. Choose each parent’s ABO group and Rh factor and it highlights every blood type their child could have, while greying out the ones that are genetically impossible.
That impossible list is where the tool earns its keep, because the rules produce some firm, counter-intuitive certainties. Two type-O parents can have only type-O children, since O is the only allele either can pass. A type-AB parent can never have a type-O child, because AB carries no O allele to give. And if both parents are Rh-negative, every child will be Rh-negative, whereas a single Rh-positive parent leaves both possibilities open. The eight-cell grid makes these patterns visible at a glance, turning an abstract Punnett-square exercise into something you can simply read off.
A few honest caveats matter. The calculator shows which outcomes are possible, not their exact probabilities, because a visible blood group does not always reveal the hidden genotype — a type-A parent might be AA or AO, and only that detail would set the odds. It also covers the standard ABO and Rh systems, not rare exceptions like the Bombay phenotype or unusual subgroups. Most importantly, while a blood type can sometimes rule a parentage pairing out, it can never confirm one, since common blood types are shared by billions of people; real questions of parentage need a DNA test. Treat this as an educational illustration of heredity, not a medical, transfusion or legal tool — and rest assured the whole calculation happens in your browser, with nothing you select ever leaving your device.
Blood type can rule a parent out, but never rule one in — the genetics shows what’s impossible, not what’s certain.
10 Facts About Blood Types
The ABO system has alleles A, B and O.
A and B are co-dominant; O is recessive.
Two type-O parents can only have a type-O child.
Rh-positive is dominant over Rh-negative.
Type O-negative is the universal red-cell donor.
Type AB-positive is the universal plasma recipient.
An AB parent and an O parent cannot have an O child.
Rh incompatibility in pregnancy is managed with anti-D.
Blood type frequencies vary widely by population.
This tool runs in your browser — nothing is uploaded.
Frequently Asked Questions
- Blood type is set by two systems. In the ABO system, each parent passes one of two alleles — A, B or O — and the combination the child inherits determines their group. In the Rh system, a child is Rh-positive if they inherit at least one positive (D) allele. This calculator combines both to show every blood type a child of the chosen parents could have.
- Type O is recessive, meaning an O person carries two O alleles and can only pass on O. If both parents are type O, the only alleles available to the child are O and O, so the child must also be type O. It is one of the clearest rules in blood-type genetics.
- No. A type-AB parent carries one A allele and one B allele, so they can only pass on A or B, never O. Because a type-O child needs an O allele from both parents, an AB parent rules out a type-O child regardless of the other parent’s group. The calculator flags exactly these impossible combinations.
- Rh-positive is dominant over Rh-negative. A person is Rh-negative only if they carry two negative alleles. So a child can be Rh-negative only if both parents pass a negative allele — which means if both parents are Rh-negative, all their children will be Rh-negative, while if either parent is Rh-positive the child could be either.
- It tells you which types are possible and which are impossible, rather than exact percentages. That is because a parent’s visible blood group does not always reveal their underlying genotype — a type-A parent could be AA or AO — so the precise odds depend on information the blood type alone does not give. The set of possible outcomes, however, is certain.
- Only in a limited, negative way. If a child’s blood type is impossible for an alleged parent pairing, that can rule the pairing out. But it can never confirm parentage, because many people share the same common blood types. For any real question of parentage, a proper DNA test is the only reliable answer.
- If an Rh-negative mother carries an Rh-positive baby, her immune system can react to the baby’s blood, a condition called Rh incompatibility or haemolytic disease of the newborn. It is routinely prevented today with anti-D (Rho(D) immunoglobulin) injections. This is why blood typing is a standard part of antenatal care.
- O-negative red blood cells lack A, B and Rh-D antigens, so they can be given to almost anyone in an emergency, making O-negative the universal red-cell donor. At the other end, AB-positive individuals can receive red cells from any group and are the universal recipient. Plasma compatibility runs the opposite way, with AB the universal plasma donor.
- No. It is an educational genetics tool that illustrates how ABO and Rh types are inherited. It does not account for rare blood subgroups, the Bombay phenotype or other exceptions, and it should never be used for medical, transfusion or parentage decisions. Always rely on laboratory testing and professional advice for those.
- Completely free, with no account or limit. It works offline once the page has loaded and collects no data — your selections never leave your device.
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