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Punnett square · ABO + Rh

Blood Type Calculator (Child)

Calculate a child's possible blood types from the mother's and father's blood type using a Punnett square — including probability percentages and genotypes. Includes a parent compatibility check and a blood donation compatibility table.

3 modes in one tool ABO + Rh genetics Punnett square Updated: Jul 19, 2026
👩 Mother
👨 Father
Common combinations:
Enter the mother's, father's, and child's blood type to check whether this combination is biologically possible. (Not a paternity test.)
👩 Mother
👨 Father
👶 Child
Common combinations to check:
If you know the child's blood type and one parent's blood type, find the other parent's possible blood types.
👶 Child
🧑 Known parent
Common combinations:
⚙️ Display settings — Punnett square, genotype, percentages
Show Punnett squaresSeparate cross tables for ABO and Rh
Show genotypesThe parents' possible gene combinations (AA, AO, BB...)
Show probability percentagesThe likelihood of each blood type
Quick answer A child inherits one gene from each parent for both the ABO and Rh blood groups. A and B are dominant over O; A and B together make AB (codominant). Rh-positive is dominant over Rh-negative. For example, an A blood type mother and a B blood type father can have a child with any of the four ABO types: A, B, AB, or O.
4ABO blood types (A, B, AB, O)
8Total blood types (ABO × Rh)
O+Most common type (US)
O−Universal donor (emergency)
⚠️ Important — informational note: This tool is for informational purposes only; it is not a substitute for medical, legal, or professional advice. Results are a probabilistic estimate based on classical Mendelian inheritance — not a paternity test or medical diagnosis. Rare exceptions such as the Bombay phenotype, cis-AB, and rare gene mutations can break these rules. A laboratory test (and DNA test if needed) is required for a definitive result.
🩸 Blood Type Calculator — ToolPico ↗

What is a blood type calculator, and how does it work?

A complete guide to how a child's blood type is determined by the ABO and Rh systems, the Punnett square, and the difference between genotype and phenotype.

Blood type calculation predicts an unborn (or already-born) child's possible blood types from the mother's and father's blood types. Blood type is determined by two independent systems: the ABO system (A, B, AB, O) and the Rh factor (positive/negative). Both traits follow classical Mendelian inheritance — each parent randomly passes on one of their two genes (alleles) to the child. This tool crosses every possible gene combination (a Punnett square) to work out the result.

How is ABO blood type inherited?

Quick answerThe ABO system has three alleles: A, B, and O. A and B are dominant, O is recessive; when A and B occur together, both are expressed (codominant → AB). Everyone carries two alleles: type A can be genotype AA or AO, type B can be BB or BO, type AB is AB, and type O is OO. Each parent passes on one of these two alleles to the child.
  • The A gene and B gene are dominant: even a single copy shows up in the phenotype.
  • The O gene is recessive: it only shows up when paired with another O (OO). This is why an AO person looks like type A from the outside but can still pass on the O gene.
  • A and B are codominant: when inherited together, they form the AB blood type.

Because of this "hidden O gene," two type-A parents can have a type-O child (AO × AO → OO). The calculator's result accounts for every possible genotype hiding beneath a parent's visible (phenotype) blood type.

How is the Rh factor inherited, and what is Rh incompatibility?

Quick answerThe Rh factor is a separate gene: Rh+ (D) is dominant, Rh− (d) is recessive. An Rh+ person can be DD or Dd; an Rh− person is always dd. The child of two Rh− parents is always Rh−. Rh incompatibility becomes a concern when an Rh− mother carries an Rh+ baby, and requires monitoring during pregnancy.

Rh incompatibility can arise when an Rh-negative mother's immune system produces antibodies against her Rh-positive baby's blood; today it is largely prevented with an anti-D (Rhogam) injection. This tool only shows the probability — always consult your doctor for prenatal care.

Can a child's blood type differ from both parents'?

Quick answerYes, and it's completely normal. For example, if the mother is AO and the father is BO, both can pass on the O gene, so the child can be O. Likewise, A×B parents can produce a child of type A, B, AB, or O — all four are possible. A blood type that differs from the parents' does not by itself imply a question of paternity.

Child's blood type by parents' blood type (combination table)

All 16 mother × father ABO combinations and the child's possible blood types for each. (Rh is calculated separately; two Rh− parents always have an Rh− child.)

ABO inheritance — mother × father → child's possible types
Mother × FatherChild's possible ABO types

Popular blood type combinations

Related mini calculators: donation, Rh risk, genotype

The three most common blood-type questions, solved in one click. Everything below runs entirely in your browser.

🩸Blood donation compatibility
Who can a given blood type donate to, and receive from? (Red blood cell / whole blood compatibility.)
🤰Rh incompatibility risk
Based on the mother's and father's Rh status, is there a chance of Rh incompatibility during pregnancy?
🧬Genotype solver
Which gene combinations (genotypes) can produce a given visible blood type (phenotype)?

Blood type reference tables

Citable data: Rh inheritance, transfusion (donation) compatibility, US blood type distribution, and genotype-phenotype matches.

Rh factor inheritance (Rh+ dominant, Rh− recessive)
Mother Rh × Father RhChild's possible Rh
Rh− × Rh−Rh− only (100% certain)
Rh+ × Rh−Rh+ or Rh−
Rh− × Rh+Rh+ or Rh−
Rh+ × Rh+Rh+ or Rh− (if both parents carry Dd)

Rh incompatibility risk only arises with an Rh− mother + Rh+ baby; it can be prevented with anti-D (Rhogam). Doctor follow-up during pregnancy is essential.

Transfusion / blood donation compatibility (red blood cells)
TypeCan donate toCan receive from
O Rh−Everyone (universal donor)O Rh− only
O Rh+O+, A+, B+, AB+O+, O−
A Rh−A−, A+, AB−, AB+A−, O−
A Rh+A+, AB+A+, A−, O+, O−
B Rh−B−, B+, AB−, AB+B−, O−
B Rh+B+, AB+B+, B−, O+, O−
AB Rh−AB−, AB+AB−, A−, B−, O−
AB Rh+AB+ onlyEveryone (universal recipient)

This table summarizes red blood cell compatibility; plasma compatibility runs the other way. The actual transfusion decision is made by a clinician after cross-matching.

Approximate blood type distribution in the United States
Blood typeApprox. share
O+~37%
A+~36%
B+~9%
AB+~3%
O−~7%
A−~6%
B−~2%
AB−~1%

Approximate, rounded figures; exact shares vary slightly by source. About 82-85% of the US population is Rh positive.

Genotype → phenotype (visible blood type) mapping
GenotypeVisible (phenotype) blood type
AA or AOType A
BB or BOType B
ABType AB
OOType O
DD or DdRh positive (+)
ddRh negative (−)

Phenotype is the visible blood type; genotype is the underlying gene combination. Because A and B are dominant, AO and AA both show up as type A.

Add this calculator to your site (embed code)

Embed the blood type calculator on your own website for free. Copy the code below into your HTML — the tool runs in a simplified view and links back to this page as its source.

The embedded tool has a fixed layout; you can adjust the height value to fit your site. No ads or personal data, runs entirely client-side.

Blood type and genetics glossary

Short definitions of the core terms used in blood type inheritance.

ABO systemThe system that classifies blood types as A, B, AB, and O, based on antigens on the surface of red blood cells.
Rh factorWhether the D antigen is present on red blood cells — positive (+) if present, negative (−) if absent.
Allele (gene)A version of a gene for a given trait. The ABO system has A, B, and O alleles.
GenotypeThe specific gene combination a person carries (e.g. AO, BB, dd). Invisible, but it's what gets passed to a child.
PhenotypeThe visible expression of a genotype — the blood type actually seen in a lab test (A, B, AB, O).
DominantAn allele that shows up in the phenotype even with a single copy. A, B, and Rh+ (D) are dominant.
RecessiveAn allele that only shows up with two copies. O and Rh− (d) are recessive.
CodominantWhen two alleles are both expressed together. A and B together produce the AB blood type.
Punnett squareA grid that crosses parental alleles to show the possible genotypes of the offspring.
HomozygousCarrying two copies of the same allele (AA, BB, OO, DD, dd).
HeterozygousCarrying two different alleles (AO, BO, AB, Dd). Also called a "carrier."
Universal donor / recipientO Rh− can donate to anyone (universal donor); AB Rh+ can receive from anyone (universal recipient).
Rh incompatibilityA mismatch between an Rh− mother and an Rh+ baby; prevented with an anti-D injection.
Bombay phenotypeAn extremely rare condition where a person types as O but genetically carries A/B genes, breaking the usual rules.

In-depth guides

Detailed answers to the most common blood type questions.

Which parents can have an O Rh-negative child?

For a child to be type O, both parents must be able to pass on an O gene. This means the parents can be type O (OO) themselves, or they can appear as type A or B while secretly carrying O (AO, BO). For example, AO × BO parents can produce an O child.

For an Rh-negative child, both parents must carry at least one d (Rh−) gene. The child of two Rh-negative parents is always Rh-negative; even two Rh-positive parents can have a 25% chance of an Rh-negative child if both happen to be Dd carriers.

Which combinations can produce an AB blood type child?

For an AB child, one parent must pass on the A gene and the other the B gene. The combinations that make this possible are A × B, A × AB, B × AB, and AB × AB. AB is possible in these cases, but not guaranteed — for example, AO × BO parents can produce an AB child or an O child.

A type-O parent (OO) can only pass on the O gene, so if either parent is type O, the child cannot be AB. The one exception is the very rare condition known as cis-AB.

Is blood type proof of paternity? (exceptions)

Blood type cannot prove paternity — it can only rule out some possibilities. For example, a type-O child born to a type-AB parent is not genetically expected — but even this can be misleading in rare cases like the Bombay phenotype.

A child's blood type appearing consistent with the parents does not mean no one else could be the father, because the same blood type is common across the population. Only a DNA test can give a definitive answer. This tool is not a medical or legal decision-making tool.

Frequently asked questions

What blood type will a child have based on the parents' blood types?
In the ABO system, a child inherits one gene (allele) from each parent. A and B genes are dominant, and the O gene is recessive; A and B together form AB (codominant). For example, if the mother is type A and the father is type B, the child can be A, B, AB, or O. If both parents are type O, the child will only be type O. The Rh factor is inherited the same way from each parent, and Rh-positive is dominant.
What blood type will a child have if both parents are O Rh-negative?
If both parents are O Rh-negative (OO, dd), the child will always be O Rh-negative. Since type O is recessive, two O parents can only pass on the O gene; since Rh-negative is also recessive, the child of two Rh-negative parents is always Rh-negative. This is one of the rare cases where the result is 100% certain.
Which parent combinations can produce an AB blood type child?
For an AB child, one parent must pass on the A gene and the other the B gene. The combinations A×B, A×AB, B×AB, and AB×AB can all produce an AB child. Combinations like O×O, A×O, or B×O cannot produce an AB child (aside from the very rare cis-AB exception), because a type-O parent doesn't carry an A or B gene.
How is blood type inherited? (What is a genotype?)
Every person carries two ABO alleles. Type A can be genotype AA or AO, type B can be BB or BO, type AB is AB, and type O is OO. The mother and father each randomly pass on one of these two alleles to the child. An AO person appears as type A but can still pass on the O gene — what matters for inheritance is the underlying genotype, not the visible type.
What is Rh incompatibility?
Rh incompatibility can occur when an Rh-negative mother carries an Rh-positive baby. The mother's immune system may produce antibodies against the baby's Rh-positive blood, which can pose a risk in later pregnancies. Today it is largely prevented with an anti-D (Rhogam) injection. This tool only shows the probability — always consult your doctor during pregnancy.
Can a child's blood type be different from both parents'?
Yes. For example, if the mother is AO and the father is BO, both can pass on the O gene and the child ends up type O — meaning a mother who is A and a father who is B can have an O child. Even two type-A parents (AO × AO) can have an O child. A blood type that differs from the parents' is genetically normal and does not by itself suggest a question of paternity.
Can two type-O parents have a type-A child?
No. The genotype of type O is OO, carrying only the O gene. Since two type-O parents can only pass on the O gene, the child will always be type O; A, B, or AB is not possible. A type-A child requires at least one parent to carry the A gene. The extremely rare Bombay phenotype is the one visible exception to this rule.
Does a blood type calculator replace a paternity test?
No. Blood type can only rule out or support a possibility; it cannot prove paternity. Even if a child's blood type looks consistent with the parents, that does not mean no one else could be the father. Rare exceptions such as the Bombay phenotype, cis-AB, and rare mutations can also break the usual rules. A definitive result requires a DNA (paternity) test; this tool is not a medical or legal diagnostic tool.
Can I download or save my blood type calculator result?
Yes. After calculating a result, click the "Download result" button next to Share and Copy link to save a CSV/text summary file with the parents' and child's blood types, probabilities, and genotypes. The file is generated entirely in your browser — nothing is uploaded to a server.

Methodology & sources

🧪Reviewed by ToolPico Editorial Team — genetics & health content reviewed for accuracy against classical Mendelian inheritance references. Last reviewed: Jul 19, 2026.
ToolPico's Blood Type Calculator is a free, independent tool. The calculation engine applies the principles of classical Mendelian inheritance and the Punnett square: in the ABO system, the A, B, and O alleles are modeled with A and B dominant, O recessive, and A/B codominant; in the Rh system, D (Rh+) is dominant and d (Rh−) is recessive. When a parent's visible blood type leaves the genotype ambiguous, the tool assumes the possible genotypes are equally likely, and notes that the true ratio depends on the parent's actual genotype. Probability percentages are computed by crossing every possible gene combination.

Sources: general medical genetics and inheritance principles (ABO and Rh blood group systems). Population blood type distribution figures are approximate. Last updated: July 19, 2026. Results are for informational purposes only; a qualified laboratory and physician evaluation is required for diagnosis, paternity, or medical decisions.
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