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Predict a child's possible ABO and Rh blood types from both parents with Punnett squares and percentages, find a parent's type, and check donor charts.
The Blood Type Calculator predicts which ABO and Rh blood types a child can have from the blood types of both parents. Each type is translated into the gene pairs that can produce it — type A can be AA or AO, Rh-positive can be DD or Dd — and every combination is crossed in a Punnett square. When a parent's genotype is not known, the possibilities are weighted either by typical allele frequencies or equally, and you can set a known genotype to get exact odds. A second mode works backwards from a child and one parent to the other parent's possible types, and a third shows red-cell and plasma donor compatibility. Results are educational, not a medical or paternity test.
Open Blood Type Calculator on AltFTool — it loads instantly in your browser.
In Child's blood type, choose Parent 1's ABO group (A, B, AB or O) and Rh positive or Rh negative, then do the same for Parent 2.
If you know a genotype such as AO or Dd, pick it under ABO genotype or Rh genotype; otherwise leave Not known and choose the weighting.
Read the percentage bars for the eight blood types, the Not possible list and the ABO and Rh Punnett squares, then press Copy.
Use Find a parent's type for the reverse question, or Donor compatibility to see the red blood cell and plasma chart for your type.
Every possible child type gets a probability, and impossible types are listed separately, using genotype weighting you can see and change.
The ABO and Rh crosses are drawn for every genotype pairing, labelled with how likely each pairing is, so you can follow the genetics.
Enter a child's type and one parent's type to see which types the other parent could have and the chance each pairing gives that child.
An 8 × 8 compatibility grid for red blood cells and for plasma, plus who you can give to and receive from.
| Parents | Child can be | Child cannot be |
|---|---|---|
| O × O | O | A, B, AB |
| O × A | A, O | B, AB |
| O × B | B, O | A, AB |
| O × AB | A, B | O, AB |
| A × A | A, O | B, AB |
| A × B | A, B, AB, O | — |
| A × AB | A, B, AB | O |
| B × B | B, O | A, AB |
| B × AB | A, B, AB | O |
| AB × AB | A, B, AB | O |
Rh: two Rh− parents have only Rh− children; any pairing with an Rh+ parent can produce Rh+ or, if both carry d, Rh− children.
The ABO type is set by one gene with three common versions: A, B and O. Each parent passes one copy to the child. A and B are both dominant (codominant) over O, so AO is type A, BO is type B, AB is type AB, and only OO is type O. The Rh factor is a separate gene where Rh-positive (D) is dominant over Rh-negative (d).
Under normal inheritance, no. Two type O parents both have the genotype OO, so they can only pass on O alleles, and every child is type O. Very rare exceptions exist, such as the Bombay phenotype, where a person tests as O but carries A or B genes, so an unexpected result calls for retesting rather than conclusions.
Yes. If both parents carry one Rh-negative allele (genotype Dd), each child has a 1 in 4 chance of inheriting d from both and being Rh-negative. Two Rh-negative parents (dd × dd), however, can only have Rh-negative children. Rh is inherited independently of the ABO group, so the two are calculated separately and then combined.
Any ABO type is possible — A, B, AB or O — because an A parent may carry O and a B parent may carry O. Rh-negative is also possible if both parents carry d. The exact percentages depend on the parents' hidden genotypes; the calculator shows them under the weighting you choose, or exactly when you select known genotypes.
A type A person might be AA or AO, and this is not visible from a blood test. Equal weighting treats both as 50% likely. Allele-frequency weighting uses how common each allele is in a population, which makes AO far more likely than AA because O is the most common allele. If you know the genotype, choose it and the uncertainty disappears.
It cannot prove paternity, because millions of people share each blood type. A type combination that the standard model rules out can suggest that someone is not a biological parent, but rare genetic variants and lab errors also cause mismatches. Only DNA testing is accepted for establishing parentage.
For red blood cells, O-negative is the universal donor: it carries no A, B or RhD antigens, so it can be given to any patient in an emergency. For plasma the roles reverse — AB plasma contains no anti-A or anti-B antibodies, so AB is the universal plasma donor.
AB-positive is the universal recipient for red blood cells, because it already has A, B and RhD antigens and makes no antibodies against them. In practice hospitals still prefer to give blood of the same type and always cross-match donor and patient samples before a transfusion.
It can. If an Rh-negative mother carries an Rh-positive baby, her immune system may make antibodies against Rh-positive cells, which can affect a later pregnancy. This is routinely prevented with anti-D immunoglobulin injections, so Rh-negative mothers are tested and monitored during prenatal care.
A blood test is the only reliable way. Your doctor may already have it on record from pregnancy or surgery, blood donation centres tell donors their type, and home finger-prick kits are available. Your parents' blood types can narrow down the possibilities but cannot tell you your type for certain.
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