What this calculator does
Child blood type probability works out possible ABO and Rh blood types of a child from both parents, classic Mendelian genetics. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaPunnett square over ABO alleles (A, B dominant; O recessive) and Rh alleles (D dominant; d recessive), assuming independent assortment
The inputs explained
| Field | What to enter |
|---|---|
| Parent 1 ABO genotype | Choose from Type A (homozygous AA), Type A (carries O), Type B (homozygous BB), Type B (carries O), Type AB, Type O. |
| Parent 2 ABO genotype | Choose from Type A (homozygous AA), Type A (carries O), Type B (homozygous BB), Type B (carries O), Type AB, Type O. |
| Parent 1 Rh genotype | Choose from Rh+ (homozygous DD), Rh+ (carries d), Rh− (dd). |
| Parent 2 Rh genotype | Choose from Rh+ (homozygous DD), Rh+ (carries d), Rh− (dd). |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with parent 1 abo genotype
Every other input is held at the calculator’s starting values. Select any row to load that scenario.
How the answer changes with parent 1 abo genotype
| Parent 1 ABO genotype | Most likely blood type | Possible blood types |
|---|---|---|
| Type A (homozygous AA) | AB+ (25.0%) | 4 |
| Type A (carries O) | AB+ (12.5%) | 8 |
| Type B (homozygous BB) | B+ (50.0%) | 2 |
| Type B (carries O) | B+ (37.5%) | 4 |
| Type AB | B+ (25.0%) | 6 |
| Type O | B+ (25.0%) | 4 |