Blood Type Inheritance Calculator
Every ABO and Rh type a child can have, with Punnett squares, and the reverse check.
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- Free preview: the blood groups a child or parent can have in full, with the first rows of each table (up to 3) and the first Punnett square; every other figure is hidden.
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Rh positive or Rh negative
Chance of each blood type
The parents’ hidden genes are not known, so each chance is a range: from the least to the most likely mix of genes they could carry.
| Blood type | Chance | Estimate |
|---|---|---|
| O+ | — | |
| O− | — | |
| A+ | — | |
| A− | — | |
| B+ | — | |
| B− | — | |
| AB+ | — | |
| AB− | — |
* Not possible under the usual inheritance; see the rare exceptions below.
Punnett squares
Parent 1’s two genes run down the side and parent 2’s along the top. Each of the four boxes is equally likely, a 1 in 4 chance; the ABO and Rh squares combine by multiplying (for example ½ × ¼ = ⅛).
Every pair of genes these parents can have
Rh positive or Rh negative
Why
| Other parent | Possible? |
|---|
* Not possible under the usual inheritance; see the rare exceptions below.
Parents who can have a group O child
| Parent 1’s group in the rows, parent 2’s in the columns | O | A | B | AB |
|---|
Parent 1’s group in the rows, parent 2’s along the top. Blood groups only: any pair can have an Rh negative child if both carry d, and an Rh positive child needs at least one Rh positive parent.
Rare exceptions, and why this is not a paternity test
- Bombay phenotype (hh): people who make no H antigen test as group O but can carry and pass on A or B genes, so two “O” parents can have an A or B child. It affects about 1 in 10,000 people in India and 1 in a million in Europe.
- cis-AB: a single gene that makes both A and B, so an AB parent can have an O child, or an O parent an AB child. It is most common in Korea and East Asia.
- Weak D and partial D: some Rh positive people make little D, and laboratories differ on whether to report them as Rh positive or negative.
- Illness: some infections and blood cancers can change how blood groups type, and blood groups can be typed or written down wrongly.
Blood types can show only that a person could be a biological parent, never that they are, and an “impossible” combination is not proof that they are not. Only a DNA test can establish parentage.
Blood group chart: parents and children
| Parents | Child can be | Child cannot be* |
|---|---|---|
| O × O | O | A, B, AB |
| O × A | O, A | B, AB |
| O × B | O, B | A, AB |
| O × AB | A, B | O, AB |
| A × A | O, A | B, AB |
| A × B | O, A, B, AB | — |
| A × AB | A, B, AB | O |
| B × B | O, B | A, AB |
| B × AB | A, B, AB | O |
| AB × AB | A, B, AB | O |
* Under the usual inheritance. Rh: two Rh negative parents have Rh negative children; any other pair can have either.
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For general information only, not medical advice. Consult a qualified health professional for advice about your situation.
How this tool is checked
- Sources
-
This guide lists 6 sources under ‘Sources’, among them:
- Dean L, Blood Groups and Red Cell Antigens
- A “new” blood group character related to the ABO system
- cis-AB: Yazer MH, Olsson ML, Palcic MM, The cis-AB blood group phenotype: fundamental lessons in glycobiology
- Tests
- 21 automated tests check its results.
- Found an error?
- Report a problem or write to support@mysmartcopilot.com, with what you entered and the result you expected.
About the Blood Type Inheritance Calculator
A blood type is two inherited traits: the ABO group (O, A, B or AB) and the Rh factor (positive or negative). Each parent passes on one of their two ABO genes and one of their two Rh genes, so a child’s blood type follows from the parents’ genes, not simply from their blood types. This calculator lists every blood type a child can have, with the chance of each and the Punnett squares behind it. In reverse, it shows which blood types the other parent can have, given a child’s type and, if you know it, one parent’s.
A blood test does not show which genes a person carries: group A can be AA or AO, and Rh positive can be DD or Dd. So the chances are ranges unless you know the parents’ hidden genes, and an optional estimate weights them by how common each gene is. Rare exceptions such as the Bombay phenotype are explained below, and blood types are never a paternity test.
Without a pass, the free preview shows the blood groups a child or parent can have in full, with the Rh factor, the first rows of each table, the first Punnett square and the first line of why; the chances of every blood type, the estimate, the other square, every gene pair and Copy result come with a Pro pass.
How to use it
- Choose The child’s possible types, then each parent’s blood group and Rh factor. Choose Not known for a parent whose type you do not know.
- If you know a parent’s hidden gene, for example because one of their own parents is group O, choose it (AO, BO or Dd). The hint under each list says when it is certain.
- Read the possible types and the chance of each. To see one estimate per type, choose population figures or type your own.
- Look at the Punnett squares, and pick a pair of genes to see how each combination arises.
- To check a child’s type against the parents, choose The parents’ possible types, then enter the child’s type and, if known, one parent’s type.
Examples
The child is group O: Rh positive (75–100%) or Rh negative (0–25%). Never A, B or AB.
A+, A−, O+ and O−, exactly 25% (1 in 4) each.
Any group: O 0–25%, A 0–50%, B 0–50%, AB 25–100%.
Group A or B, 50% each; never AB or O.
The other parent can be group O, A or B, Rh positive or negative, but not AB.
How blood types are inherited
The ABO gene has three common forms (alleles): A and B, which are codominant, and O, which makes neither antigen. Six gene pairs give the four groups: AA or AO is group A, BB or BO is group B, AB is group AB and OO is group O. The Rh(D) gene comes as D, which makes the D antigen, or d, usually a missing RHD gene; D is dominant, so DD and Dd are Rh positive and only dd is Rh negative. Textbooks also write the ABO alleles as Iᴬ, Iᴮ and i.
Each parent passes on one of their two alleles of each gene, each with a 1 in 2 chance, so a Punnett square has four equally likely boxes. The ABO gene is on chromosome 9 and RHD on chromosome 1, so they are inherited independently and their chances multiply: a 1 in 2 chance of group O and a 1 in 4 chance of Rh negative make a 1 in 8 chance of O−.
Why the chances are ranges, and the estimate
Two group A parents have no O child if either of them is AA, and a 1 in 4 chance with each pregnancy if both are AO. A blood test cannot tell these apart, so the calculator shows the lowest and highest chance over the genes the parents could carry. Family history settles it: a group A person with a group O or B parent, or with an O or B child, must be AO, and an Rh positive person with an Rh negative parent or child must be Dd.
The optional estimate weights each parent’s possible genes by how common they are, from a population’s blood group percentages, assuming Hardy–Weinberg proportions (gene pairs in the ratio p², 2pq, q²). Gene frequencies come from the group percentages by Bernstein’s method: O = √(% O), A = 1 − √(% B + % O), B = 1 − √(% A + % O). With Dean’s figures for Caucasians, for example, about 83% of group A people carry an O gene and about 56% of Rh positive people carry d. These are averages for a whole population, not facts about one family; use your own country’s figures where you have them.
Rare exceptions
- Bombay phenotype. People with no working H gene (hh) cannot make the H antigen that A and B are built on, so they test as group O whatever ABO genes they carry and can pass on A or B. It was first described in Bombay (Mumbai) and affects about 1 in 10,000 people in India and about 1 in a million in Europe.
- cis-AB. A rare ABO allele makes one enzyme with both A and B activity, so both antigens come from a single parent: an AB parent can have an O child, and an O parent can have an AB child. It is the most frequent ABO subgroup in Korea and is more frequent in East Asia than elsewhere.
- Weak D and partial D. Some people make less D antigen, or part of it, and laboratories differ on whether to report them as Rh positive or Rh negative, so the same person can be reported both ways.
- Illness and errors. Some infections can make group A blood test like group B for a while, blood cancers can weaken A and B antigens, and a blood type can be typed or written down wrongly.
Not a paternity test
Blood types can show only that someone could be a biological parent, never that they are: millions of people share each blood type. And because of the exceptions above, an “impossible” combination is not proof that someone is not a parent either; it is a reason to recheck the blood types. Only a DNA test can establish parentage.
Sources
- Dean L, Blood Groups and Red Cell Antigens, NCBI Bookshelf: the ABO blood group (inheritance, phenotype frequencies, acquired and weakened antigens), the Hh blood group (the Bombay phenotype), the Rh blood group (D-negative frequencies, weak and partial D) and hemolytic disease of the newborn.
- The first description of the Bombay phenotype: Bhende YM, Deshpande CK, Bhatia HM et al., A “new” blood group character related to the ABO system, The Lancet.
- cis-AB: Yazer MH, Olsson ML, Palcic MM, The cis-AB blood group phenotype: fundamental lessons in glycobiology; Chun S et al., Cis-AB, the blood group of many faces.
- Weak D: Sandler SG et al., College of American Pathologists work group, It’s time to phase in RHD genotyping for patients with a serologic weak D phenotype.
- Blood group terminology: the ISBT Working Party on Red Cell Immunogenetics and Blood Group Terminology, whose numbers make ABO system 001, Rh 004 and H 018.
- Hardy–Weinberg proportions: OpenStax Biology 2e, 19.1 Population Evolution.
Limitations
- Only the ABO and RhD groups are covered, not the other blood group systems (Kell, Duffy, MNS and dozens of others).
- Rare variants (Bombay, cis-AB, weak and partial D, weak A and B subgroups) are explained but not calculated.
- The estimate uses whole-population figures and assumes Hardy–Weinberg proportions. The listed figures are Dean’s for three broad groups and describe no particular country; your own country’s figures, or the family’s blood types, give a better answer.
- Each pregnancy is independent: a 1 in 4 chance does not mean one child in every four.
Privacy
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Frequently asked questions
What do I get without a pass?
Without a pass, Blood Type Inheritance Calculator shows the blood groups a child or parent can have in full, with the first rows of each table (up to 3) and the first Punnett square; every other figure is hidden. Until you unlock it, the result can’t be copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Can two group O parents have a group A or B child?
Not under the usual inheritance: O parents can pass on only O genes, so their children are group O. The rare exception is the Bombay phenotype, in which a parent who tests as O carries A or B genes. A blood type that was typed or written down wrongly can also explain it, so recheck the blood types first.
Can two Rh positive parents have an Rh negative baby?
Yes, if both carry the d gene (both are Dd). Then each child has a 1 in 4 chance of being Rh negative. If either parent is DD, all their children are Rh positive.
I am O+ and my partner is A+. What blood type will our baby have?
Group O or A, Rh positive or negative. Group O is 0–50% likely (it needs your partner to carry O), group A 50–100%, and Rh negative 0–25% (it needs both of you to carry d). Enter your types above to see every combination.
Can an AB parent have an O child?
Normally not, because an AB parent passes on either A or B. The rare exception is cis-AB, where one gene carries both A and B, so the other gene can be O.
Why does the Rh factor matter in pregnancy?
If an Rh negative mother carries an Rh positive baby (with D from the father), she can make anti-D antibodies, usually around the birth of a first Rh positive baby. In a later pregnancy they can cross the placenta and attack an Rh positive baby’s red cells (haemolytic disease of the newborn). Antenatal care screens for this and gives preventive treatment, so ask your midwife or doctor.
Can blood types prove who the father is?
No. They can only show that a man could be the father, and because of rare exceptions even an “impossible” combination is not proof. Only a DNA test can establish parentage.