Blood type calculator
The blood groups a child can inherit, gene by gene.
- Possible groups
- A, O
Output
The child can be: A, O The child cannot be: B, AB By the parents’ genes: AA × OO: A 100% AO × OO: A 50%, O 50% Rare variants such as cis-AB and the Bombay phenotype break these rules: a blood group never proves or rules out parentage — only a DNA test does.
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Example
Example: an O+ mother and an AB− father — which groups can the child have?
Mode: Both parents’ groups. Parent’s blood group O with Rh positive; other parent’s blood group AB with Rh negative.
- An O parent is always OO and passes on O; an AB parent passes on A or B. So the one pairing, OO × AB, gives A 50 % and B 50 %.
- An Rh+ parent may carry the Rh− gene, so the child can be Rh+ or Rh−.
| Parents | Child can be | Child cannot be |
|---|---|---|
| O × O | O | A, B, AB |
| A × O | A, O | B, AB |
| B × O | B, O | A, AB |
| A × A | A, O | B, AB |
| A × B | A, B, AB, O | — |
| AB × O | A, B | AB, O |
| AB × A | A, B, AB | O |
| AB × AB | A, B, AB | O |
The child can be A+, A−, B+ or B−, and not AB or O, under the usual rules. Rare variants such as cis-AB and the Bombay phenotype break them, so a blood group never proves or rules out parentage.
How it works
- Choose both parents’ blood groups, and their Rh factor if you know it.
- See the groups the child can and cannot have, and for each pairing of the parents’ genes the share of each group.
- Or choose “one parent’s group and the child’s” to see which groups the other parent can have.
Frequently asked questions
- How is blood type inherited?
- Each parent passes one of their two ABO genes. A is AA or AO, B is BB or BO, AB is AB and O is OO; A and B are dominant over O. So two A parents who are both AO can have an O child, one time in four.
- Why no single percentage?
- Because a blood test shows the group, not the genes behind it: an A parent may be AA or AO. The calculator gives the shares for each possible pairing instead of guessing which one your family has.
- How is Rh inherited?
- Rh positive is dominant: an Rh+ parent may carry the Rh− gene. Two Rh− parents have Rh− children; any other pairing can have either.
- Can blood type prove who the father is?
- No. Rare variants such as cis-AB and the Bombay phenotype break the usual rules, so a blood group can neither prove nor rule out parentage. Only a DNA test can.
- Can two O parents have a child with blood type A?
- Not under the usual ABO rules: O parents are both OO and can only pass on O, so the calculator lists O alone. Rare exceptions such as the Bombay phenotype are why only a DNA test settles parentage.
- Can an AB parent have an O child?
- Not under the usual rules: an AB parent passes on A or B, never O. With an O partner the child is A or B; with an A, B or AB partner, A, B or AB. The rare cis-AB variant is the known exception.
- Is anything uploaded?
- No. It is worked out in your browser, and nothing you type leaves your computer.
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