Blood Type Calculator
Choose both parents' blood types to see which ABO and Rh blood types a child could inherit — and which are impossible.
Blood type is inherited from both parents. The ABO type comes from the A, B and O gene versions (alleles), and the Rh factor (the + or −) is inherited separately. Because a parent can carry a hidden O or Rh− allele, this tool shows every type a child could have.
How blood type is inherited
Each parent passes one ABO allele and one Rh allele. A and B are dominant over O; Rh positive is dominant over Rh negative. So two type-A parents can still have a type-O child if both carry an O allele, and two Rh-positive parents can have an Rh-negative child.
| Parent type | Alleles it can pass |
|---|---|
| A | A or O |
| B | B or O |
| AB | A or B |
| O | O only |
Worked example
Parent 1 is A and Parent 2 is B:
| Parent 1 can pass | A or O |
| Parent 2 can pass | B or O |
| Possible child ABO types | A, B, AB or O |
Frequently asked questions
Can two type-O parents have a non-O child?
No. Type O can only pass an O allele, so two O parents can only have an O child.
Can two Rh-positive parents have an Rh-negative baby?
Yes, if both parents carry a hidden Rh-negative allele. Rh positive is dominant, so carriers still show as positive.
Can this prove parentage?
No. Blood type can sometimes rule a parent out, but it can never confirm parentage. Only DNA testing can do that.
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For general information and education only — not medical advice or a paternity test. Rare genetic exceptions exist. Consult a healthcare professional for medical questions.