Blood Type Calculator
Predict a child's possible blood types based on the parents' ABO and Rh blood types using Punnett square genetics.
Parent 1
Parent 2
Possible Child Blood Types
ABO Probabilities
Rh Factor Probabilities
What Are Blood Types?
Blood types are determined by the presence or absence of specific antigens — proteins and sugars on the surface of red blood cells. The two most important blood group systems are the ABO system and the Rh system.
Your blood type is inherited from your parents and is determined by the genes you receive. Knowing your blood type is crucial for safe blood transfusions, organ transplantation, and understanding pregnancy compatibility.
The ABO Blood Group System
The ABO system was discovered by Karl Landsteiner in 1901 (earning him the Nobel Prize in 1930). It classifies blood into four types based on the presence of A and/or B antigens:
| Blood Type | Antigens on RBCs | Antibodies in Plasma | Possible Genotypes |
|---|---|---|---|
| Type A | A antigen | Anti-B | AA or AO |
| Type B | B antigen | Anti-A | BB or BO |
| Type AB | Both A and B antigens | Neither | AB only |
| Type O | Neither antigen | Both Anti-A and Anti-B | OO only |
The A and B alleles are codominant (both expressed when present together → AB), while O is recessive (only expressed when two O alleles are inherited).
The Rh Blood Group System
The Rh system determines whether you are Rh positive (+) or Rh negative (−), based on the presence of the RhD antigen:
- Rh+ (positive): RhD antigen is present. Genotype can be DD (homozygous) or Dd (heterozygous)
- Rh− (negative): RhD antigen is absent. Genotype is always dd (homozygous recessive)
The Rh+ allele (D) is dominant over Rh− (d). This means two Rh+ parents can have an Rh− child if both carry the recessive d allele (both are Dd).
How Blood Type Inheritance Works
Each person inherits one ABO allele from each parent. The combination determines the child's blood type. Since we don't know whether a Type A parent is AA or AO (or Type B is BB or BO), the calculator assumes equal probability of homozygous and heterozygous genotypes.
Type B parent → 50% chance BB, 50% chance BO
Type AB parent → always AB
Type O parent → always OO
Blood Type Compatibility for Transfusion
| Blood Type | Can Donate To | Can Receive From |
|---|---|---|
| O− | Everyone (Universal Donor) | O− |
| O+ | O+, A+, B+, AB+ | O+, O− |
| A− | A−, A+, AB−, AB+ | A−, O− |
| A+ | A+, AB+ | A+, A−, O+, O− |
| B− | B−, B+, AB−, AB+ | B−, O− |
| B+ | B+, AB+ | B+, B−, O+, O− |
| AB− | AB−, AB+ | A−, B−, AB−, O− |
| AB+ | AB+ only | Everyone (Universal Recipient) |
Blood Type Distribution Worldwide
| Blood Type | Approximate Frequency |
|---|---|
| O+ | 37.4% |
| A+ | 35.7% |
| B+ | 8.5% |
| AB+ | 3.4% |
| O− | 6.6% |
| A− | 6.3% |
| B− | 1.5% |
| AB− | 0.6% |
Rh Incompatibility in Pregnancy
When an Rh-negative mother carries an Rh-positive baby, her immune system may produce antibodies against the baby's RhD antigen. This is called Rh sensitization or hemolytic disease of the newborn (HDN). It typically doesn't affect the first pregnancy but can be dangerous in subsequent pregnancies.
Prevention involves administering Rh immunoglobulin (RhoGAM) at 28 weeks of pregnancy and within 72 hours of delivery. This prevents the mother from developing anti-D antibodies.
Frequently Asked Questions
Can two parents with Type O blood have a child with Type A or B?
No. Two Type O parents (both OO genotype) can only pass O alleles to their children. All children will be Type O. If a child has Type A or B, it may indicate that one parent is not the biological parent, or very rarely, a genetic mutation (Bombay phenotype).
Can two Type B parents have a Type O child?
Yes! If both Type B parents carry the O allele (genotype BO), each has a 50% chance of passing the O allele. The probability of the child being Type O is 25% (¼).
What blood type is the universal donor?
O-negative (O−) is the universal donor for red blood cell transfusions because O-negative blood cells lack A, B, and RhD antigens, so they won't trigger an immune reaction in any recipient.