Baby blood type calculator
Choose each parent's blood type and Rh factor to see which blood types the baby can have. It follows the standard ABO and Rh inheritance rules, and shows how the chances change with genes a parent can carry without it showing.
Baby's blood type (ABO)
- APossible50%–100%
- BNot possible
- ABNot possible
- OPossibleup to 50%
Baby's Rh factor
- Rh positivePossible75%–100%
- Rh negativePossibleup to 25%
Possible full blood types
- A+
- A−
- O+
- O−
Based on standard ABO and Rh inheritance. The ranges cover every hidden gene combination. Rare variants can break these rules.
How hidden genes change the chances
A blood test shows each parent's type, not which two gene copies they carry. Each row below is one possible combination, with the baby's chances for that row.
| Parent 1 carries | Parent 2 carries | A | B | AB | O |
|---|---|---|---|---|---|
| A/A | O/O | 100% | – | – | – |
| A/O | O/O | 50% | – | – | 50% |
Every parent combination
| Parents | Baby can be | Baby can't be |
|---|---|---|
| A × A | A, O | B, AB |
| A × B | A, B, AB, O | – |
| A × AB | A, B, AB | O |
| A × O | A, O | B, AB |
| B × B | B, O | A, AB |
| B × AB | A, B, AB | O |
| B × O | B, O | A, AB |
| AB × AB | A, B, AB | O |
| AB × O | A, B | AB, O |
| O × O | O | A, B, AB |
Rh factor combinations
| Parents | Rh positive | Rh negative |
|---|---|---|
| Rh positive × Rh positive | 75%–100% | up to 25% |
| Rh positive × Rh negative | 50%–100% | up to 50% |
| Rh negative × Rh negative | – | 100% |
How to use it
- Pick each parent's ABO blood type: A, B, AB or O.
- Add each parent's Rh factor if you know it. If you don't, leave it on “Don't know”.
- Read which blood types are possible. The ranges show how the chances shift with hidden genes a blood test can't see.
How the ABO blood type is inherited
Everyone has two copies of the ABO gene, one from each parent, and passes one of them on to each child. There are three common versions: A, B and O. A and B show up whenever they are present, while O only shows when a person has two O copies.
That's why a blood test doesn't tell the whole story. Type A can mean two A copies or one A and a hidden O, and type B works the same way. Type AB always means one A and one B, and type O always means two O copies. The calculator works through every hidden combination, which is where the ranges come from.
How the Rh factor is inherited
The Rh factor (RhD) is inherited separately from the ABO type. Rh positive shows up with a single copy, so an Rh-positive parent may carry a hidden negative copy. Rh-negative parents have two negative copies.
Two Rh-negative parents have an Rh-negative baby. An Rh-positive and an Rh-negative parent can have a baby of either type, and so can two Rh-positive parents if both carry a hidden negative copy.
Rh negative in pregnancy
If the mother is Rh negative and the baby is Rh positive, her immune system can make antibodies against the baby's blood cells. This usually matters for later pregnancies rather than the first, and it is largely preventable.
Antenatal care checks the mother's blood group early in pregnancy. Where the baby may be Rh positive, Rh-negative mothers are offered anti-D immunoglobulin injections to stop antibodies forming. Ask your midwife or doctor what applies to you.
When the rules don't fit
- Rare inherited variants can break the usual rules. With cis-AB, A and B are passed on together from one parent, so an AB parent and an O parent can have an AB or O baby.
- People with the rare Bombay phenotype test as type O but can still pass on A or B, so parents who look like type O can have an A or B baby.
- Blood typing and records can also be wrong, so an unexpected result is worth rechecking.
- Blood type alone can't reliably prove or rule out who a child's parents are. Only a DNA test can do that.
Frequently asked questions
How do I work out my baby's blood type?
Each parent passes on one of their two ABO gene copies. Pick both parents' blood types above and the calculator lists every type the baby can have. For example, parents with types A and O can have an A or O baby, but not B or AB.
Can two O parents have a baby with a different blood type?
Not with standard inheritance. Two O parents can only pass on O, so the baby is type O. Rare variants such as the Bombay phenotype are the exception.
Can a baby have a blood type neither parent has?
Yes. Parents with types A and B can have an O baby if both carry a hidden O copy, or an AB baby. Two type A parents can also have an O baby.
Does the baby get the mother's or the father's blood type?
Neither one in particular. The baby gets one ABO copy and one Rh copy from each parent, so the blood type can match the mother's, the father's, both or neither.
Can blood type show who the father is?
No. Blood type only shows whether a combination fits the usual rules, and rare variants or testing errors can make a real family look impossible. Only a DNA test can confirm parentage.
How common is each blood type?
It depends on where your family comes from. In the UK, for example, about 48% of people are group O and about 85% are RhD positive, according to the NHS.