Baby Blood Type Calculator
Enter both parents' blood types to see which ABO and Rh types your baby could have, which are not possible, and the chance of each. Add grandparents if you know them to make the result more exact.
Accuracy: high
Enter both parents' blood types
Choose each parent's ABO group and Rh factor (for example A+ or O−). You can find it on a blood donor card, a pregnancy blood test or your medical records.
ABO and Rh blood groups follow well-understood inheritance rules, so the list of possible and not possible types is reliable for almost all families. Exact chances can depend on hidden genes, which is why some are shown as a range.
Your baby could have
Not possible (under standard inheritance)
Chance of each blood type
Chance in every case Extra chance if a parent carries a hidden gene
One parent is Rh-negative and your baby could be Rh-positive. If the birth parent is Rh-negative and the baby is Rh-positive, the pregnancy needs a little extra care (called Rh incompatibility). It is well managed today, usually with a blood test and an Rh immune globulin injection. Please ask your doctor or midwife about it.
Punnett square
Each parent passes on one ABO gene (A, B or O) and one Rh gene (D = Rh+, d = Rh−). The 16 squares are 16 equally likely combinations. Where a parent's genes are uncertain, switch between the possibilities to see how the result changes.
🔒 Calculated on your device. Nothing you entered was sent or saved.
Share your result
A picture of your result, made inside your browser. It is only shared if you choose to send or save it.
Understanding your result
- Possible and not possible types follow standard ABO and Rh inheritance. This part is reliable for almost every family.
- A single percentage, such as 50%, means the chance is the same whatever hidden genes the parents carry.
- A range, such as 0%–25%, means the chance depends on a hidden gene. A type A parent can be AA or AO, and an Rh-positive parent can be DD or Dd. The low number is the chance if no hidden gene is passed on; the high number is the chance if the parents carry it.
- The Punnett square shows all 16 equally likely gene combinations for one set of parent genes. Switch the buttons above the square to see each possibility.
How the blood type calculator works
- Possible genes for each parent. Type O = OO, A = AA or AO, B = BB or BO, AB = AB. Rh-positive = DD or Dd, Rh-negative = dd.
- Grandparents narrow it down. Each parent got one gene from their mother and one from their father. A type A parent with a type O or B parent must be AO. An Rh-positive parent with an Rh-negative parent must be Dd.
- Every combination is checked. For each possible set of parent genes, the calculator builds the Punnett square: each parent passes one ABO gene and one Rh gene, giving 16 equally likely combinations.
- The result is the full range. A type is "possible" if it appears in any combination. Its chance is shown from lowest to highest across the combinations, so we never invent a single number the genetics cannot support.
The full rules are on our methodology page.
The genetics of baby blood type
ABO: three versions of one gene
The ABO gene has three common versions, called alleles: A, B and O. Every person has two copies, one from each parent. A and B are codominant, so a person with one of each is type AB. O is recessive, so a person is type O only with two O copies. This is why two type A parents (both AO) can have a type O baby.
Rh factor: a separate gene
The "+" or "−" in your blood type is the RhD factor, which is inherited separately from ABO. Having at least one working RHD gene (D) makes you Rh-positive. In many people of European ancestry, Rh-negative blood comes from a missing RHD gene, and about 15% of white people are Rh-negative (Dean, NCBI).
Parent blood type chart
This chart shows every ABO combination of parents and the possible types for their baby. Ranges depend on hidden O genes.
| Parents | Baby could be | Not possible |
|---|---|---|
| O × O | O (100%) | A, B, AB |
| O × A | O (0%–50%), A (50%–100%) | B, AB |
| O × B | O (0%–50%), B (50%–100%) | A, AB |
| O × AB | A (50%), B (50%) | O, AB |
| A × A | O (0%–25%), A (75%–100%) | B, AB |
| A × B | O (0%–25%), A (0%–50%), B (0%–50%), AB (25%–100%) | — |
| A × AB | A (50%), B (0%–25%), AB (25%–50%) | O |
| B × B | O (0%–25%), B (75%–100%) | A, AB |
| B × AB | A (0%–25%), B (50%), AB (25%–50%) | O |
| AB × AB | A (25%), B (25%), AB (50%) | O |
| Parents' Rh factors | Baby Rh+ | Baby Rh− |
|---|---|---|
| Rh+ × Rh+ | 75%–100% | 0%–25% |
| Rh+ × Rh− | 50%–100% | 0%–50% |
| Rh− × Rh− | Not possible | 100% |
Accuracy and limitations
- Possible and not possible types are reliable under standard inheritance, which covers almost all families.
- Rare variants can break the usual rules, for example the Bombay blood type and other unusual ABO or RhD variants.
- Exact chances often depend on hidden genes that a blood type cannot show, so we give ranges instead of guesses.
- The calculator covers ABO and RhD only, not other blood group systems such as Kell or Duffy.
- It is not a paternity test, a medical test or a substitute for prenatal blood tests.
Frequently asked questions
Can two O parents have an A or B baby?
Under standard inheritance, no. Two type O parents can only pass on O genes, so their children are type O. Very rare exceptions exist, such as the Bombay blood type, where a person tests as O but carries A or B genes. A wrong blood test entry is a more common explanation. If this matters for your family, ask a doctor or genetic counselor rather than relying on a calculator.
Can two Rh-positive parents have an Rh-negative baby?
Yes. A parent can be Rh-positive while carrying one hidden Rh-negative gene (Dd). If both parents carry one and both pass it on, the baby is Rh-negative. When both parents are Dd, the chance is 25% (1 in 4). If either parent has no hidden Rh-negative gene, the chance is 0%.
Can a baby have a different blood type from both parents?
Yes. For example, an A parent and a B parent can have an O baby (if both carry a hidden O) or an AB baby. A baby's blood type comes from one gene from each parent, so the combination can differ from either parent.
Why are some chances shown as a range?
Because a blood type does not always reveal both genes. Type A can be AA or AO, and Rh-positive can be DD or Dd. We show the lowest and highest chance across these possibilities instead of guessing. Adding grandparents' blood types can narrow or remove the range.
Can this calculator prove or rule out paternity?
No. It is an educational tool. Blood types can hint that a result is unexpected, but rare blood group variants and lab or memory errors exist. Only accredited DNA testing can answer paternity questions.
What happens if the mother is Rh-negative and the baby is Rh-positive?
This is called Rh incompatibility. The birth parent's body may make antibodies that can affect a later Rh-positive pregnancy. Mayo Clinic notes that an Rh immune globulin injection can prevent these antibodies, so talk with your doctor or midwife. It is routinely checked and managed in pregnancy care.
Scientific sources
- Dean L. The ABO blood group. In: Blood Groups and Red Cell Antigens, chapter 5. National Center for Biotechnology Information (US); 2005.
- Dean L. The Rh blood group. In: Blood Groups and Red Cell Antigens, chapter 7. National Center for Biotechnology Information (US); 2005.
- American Red Cross. Blood types explained.
- Mayo Clinic. Rh factor blood test.