Blood Type Calculator
Select each parent's blood type (A, B, AB, or O) and Rh factor (positive or negative). The calculator shows all possible blood types for their child.
Parent 1
Parent 2
Possible Child Blood Types
Parents
A+ × B+ → 8 possible combinations
Blood Type Calculator — Predict Your Baby's Blood Type
Blood type is determined by genetics — the combination of ABO genes and Rh factors inherited from both parents. This calculator shows all possible blood types a child could have based on the parents' blood types and Rh status. It's useful for expectant parents, biology students, and anyone curious about blood type inheritance.
How Blood Type Inheritance Works
Blood type is controlled by the ABO gene system. Each parent contributes one of two alleles:
- Type A carries either AA or AO alleles
- Type B carries either BB or BO alleles
- Type AB carries one A and one B allele
- Type O carries two O alleles (OO)
A and B are codominant (both expressed together), while O is recessive (only expressed when no A or B is present).
Each parent donates one allele. The child receives one allele from each parent.
Blood Type Inheritance Chart
| Parent 1 | Parent 2 | Possible Child Types |
|---|---|---|
| A | A | A, O |
| A | B | A, B, AB, O |
| A | AB | A, B, AB |
| A | O | A, O |
| B | B | B, O |
| B | AB | A, B, AB |
| B | O | B, O |
| AB | AB | A, B, AB |
| AB | O | A, B |
| O | O | O |
Rh Factor Inheritance
The Rh factor (positive or negative) is determined separately by the RHD gene:
- Rh positive (+) is dominant — a person can be ++ or +−
- Rh negative (−) is recessive — a person must be −−
| Parent 1 | Parent 2 | Possible Child Rh |
|---|---|---|
| + (could be ++ or +−) | + (could be ++ or +−) | +, − |
| + (could be ++ or +−) | − | +, − |
| − | − | − only |
Blood Type Frequency in the US Population
| Blood Type | Frequency | Can Donate To | Can Receive From |
|---|---|---|---|
| O+ | 37.4% | O+, A+, B+, AB+ | O+, O− |
| O− | 6.6% | All types (universal) | O− |
| A+ | 35.7% | A+, AB+ | A+, A−, O+, O− |
| A− | 6.3% | A+, A−, AB+, AB− | A−, O− |
| B+ | 8.5% | B+, AB+ | B+, B−, O+, O− |
| B− | 1.5% | B+, B−, AB+, AB− | B−, O− |
| AB+ | 3.4% | AB+ | All types (universal) |
| AB− | 0.6% | AB+, AB− | A−, B−, AB−, O− |
Why Knowing Your Blood Type Matters
- Medical emergencies: Receiving the wrong blood type in a transfusion can be fatal. Knowing your type speeds up emergency care.
- Pregnancy: Rh-negative mothers carrying Rh-positive babies may develop antibodies (Rh incompatibility). This is managed with RhoGAM injections.
- Blood donation: O− is the universal donor type and always in high demand. AB+ is the universal recipient.
- Health research: Some studies suggest blood type may influence susceptibility to certain diseases, including cardiovascular disease and some infections.
Frequently Asked Questions
What blood type will my baby have?
It depends on both parents' blood types. For example, if one parent is A and the other is B, the child could be A, B, AB, or O. Use the calculator above to see all possibilities based on your specific combination.
Can two type O parents have a non-O child?
No. If both parents are type O (genotype OO), they can only pass O alleles to their children. All children will be type O.
What is the rarest blood type?
AB negative (AB−) is the rarest blood type, found in only about 0.6% of the U.S. population. The rarest Rh-null type ('golden blood') is found in fewer than 50 people worldwide.
Can a child have a different blood type than both parents?
Yes. For example, if both parents are type A (genotype AO), they can have a child with type O (genotype OO) — even though neither parent is type O themselves.
What is Rh incompatibility?
Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby. The mother's immune system may produce antibodies against the baby's blood cells. This is prevented with RhoGAM injections during pregnancy.
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