This blood type calculator predicts a child’s possible ABO blood types from the two parents’ blood types — combining every genotype the parents could carry, exactly as the inheritance rules allow.
| Child’s possible blood type | Likelihood |
|---|
Probabilities blend all genotypes consistent with each parent’s type (an A parent may be AA or AO — population-typical carrier rates are not distinguished, so treat these as “possible, with rough likelihood”). The Rh factor (+/−) is inherited separately: two Rh− parents almost always have Rh− children; otherwise + is likely but not guaranteed. This is educational genetics, never a paternity test.
How ABO Inheritance Works
Your blood type comes from one gene with three allele variants — A, B and O. A and B are both dominant over O (and codominant with each other), which produces four phenotypes from six genotypes: AA and AO read as type A; BB and BO as B; AB as AB; only OO gives type O. Every child receives one allele from each parent — the same mechanics as our Punnett Square Calculator, with the twist that a parent’s visible type hides their genotype (the A parent above might secretly carry O). This calculator is part of our Biology Calculators collection.
Worked Example (Verified)
Parents of type A and B — the most surprising pairing:
- If the A parent is AO and the B parent is BO, their children can be AB, A, B or O — 25% each
- Yes, two non-O parents can have an O child: each quietly carried the recessive O allele. Blood typing has “impossible” results only in a few combinations — an AB parent cannot have an O child, and an O parent cannot have an AB child.
The Possibility Table in Words
| Parents | Children can be | Children 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 × B | O, A, B, AB | — |
| AB × AB | A, B, AB | O |
Rare exceptions exist (the Bombay phenotype, cis-AB variants, chimerism) — one more reason real paternity and clinical questions belong to DNA testing and blood banks, not calculators.
Related Tools
- Punnett Square Calculator — the general inheritance engine
- Biology Calculators — the full collection
Frequently Asked Questions
Can two parents with type A blood have a type O child?
Yes — if both are AO carriers, each child has a 25% chance of OO. The calculator’s A × A result shows exactly this.
Can an AB parent have an O child?
No (barring extremely rare genetic exceptions). AB parents pass either A or B, never O, so their children are A, B or AB.
Which blood type is the universal donor?
O-negative for red cells — it lacks A, B and Rh antigens, so it can be given to anyone in an emergency. AB-positive is the universal recipient.
How is the Rh factor (+/−) inherited?
Rh+ is dominant. Two Rh− parents have Rh− children (essentially always); an Rh+ parent may carry a hidden − allele, so + × + or + × − pairs can have either.
Can this calculator prove paternity?
No. Blood types can only sometimes exclude a possible parent (the “cannot be” column) — and even exclusion has rare biological exceptions. Paternity requires DNA testing.
Is this blood type calculator free?
Yes — free, instant, no sign-up, for education only.