Blood Type Calculator
Predict your baby's possible blood types using Mendelian genetics.
If both parents are Rh-, baby will be Rh-. Otherwise, baby can be Rh+ or Rh-.
Blood Type Genetics Explained
Blood type is determined by the ABO gene on chromosome 9. Everyone inherits one allele from each parent. The A and B alleles are co-dominant (both express), while O is recessive.
How ABO Inheritance Works
Type A blood can be genetically AA or AO. Type B can be BB or BO. Type AB is always AB (one A from one parent, one B from the other). Type O is always OO (recessive O from both parents). This creates interesting possibilities — for instance, an A parent and B parent can have children of ALL four blood types.
The Rh Factor
The Rh factor (+ or -) is determined by a separate gene. Rh+ is dominant, so a person with one Rh+ allele and one Rh- allele will be Rh+. Rh incompatibility occurs when an Rh- mother carries an Rh+ baby. Modern medicine handles this with RhoGAM injections during pregnancy.
Blood Type Distribution
In the US: O+ (37%), A+ (36%), B+ (9%), AB+ (3%), O- (7%), A- (6%), B- (2%), AB- (1%). O- is the universal donor and AB+ is the universal recipient.
Punnett Square
A parent with type A (AO genotype) and type B (BO genotype) can produce: AB, AO, BO, or OO children.