Blood Type Calculator
Use this blood type calculator to see the possible ABO and Rh blood types a child could inherit from two parents.
Updated October 22, 2026
Medical Disclaimer: This calculator gives a general estimate for education only and cannot diagnose a condition. Share your result with your doctor or the clinician who ordered your test, and do not start, stop or change any medicine based on it. Read our full Medical Disclaimer.
How Blood Type Inheritance Is Calculated
Blood type is determined by two separate genetic systems inherited independently of each other, ABO type and Rh factor. Both follow standard, well-established Mendelian inheritance patterns, which makes it possible to work out every blood type a child could possibly inherit from two known parents, even without knowing either parent's exact underlying genotype¹.
What This Calculator Measures
This shows every ABO and Rh combination a child could inherit from two parents, with the probability of each, based on standard genetics. It's an educational tool for understanding inheritance patterns, not a way to determine or confirm parentage.
The Formula
The ABO gene has three alleles: A and B are codominant, O is recessive. A person's genotype (e.g. AO, BO, AA, AB, OO) isn't directly knowable from phenotype alone for type A or B, someone with type A blood could be genotype AA or AO, and someone with type B could be BB or BO¹. This calculator presents all genotype possibilities consistent with each stated phenotype, then crosses them using a standard Punnett square.
Each child receives one of the three ABO alleles from each parent, which gives six possible genotypes and four possible blood types³.
Rh factor works separately: the D antigen present (+) is dominant over absent (−), and Rh is inherited independently of ABO type². It's calculated on its own, then combined with the ABO result to give the full range of possible blood types.
How This Calculator Computes Your Result
Enter each parent's ABO type and Rh factor. We expand each parent's stated type into every genotype consistent with it, cross all combinations, and return every possible offspring blood type along with its probability.
Possible Child Blood Types by Parent Type
This table shows the ABO results the calculator gives for each pair of parents. The percentages assume each possible genotype of a type A or type B parent is equally likely, as the calculator does.
Parents | Possible child types | Not possible |
O and O | O (100%) | A, B, AB |
O and A | A (75%), O (25%) | B, AB |
O and B | B (75%), O (25%) | A, AB |
O and AB | A (50%), B (50%) | O, AB |
A and A | A (93.8%), O (6.3%) | B, AB |
A and B | AB (56.3%), A (18.8%), B (18.8%), O (6.3%) | None |
A and AB | A (50%), AB (37.5%), B (12.5%) | O |
B and B | B (93.8%), O (6.3%) | A, AB |
B and AB | B (50%), AB (37.5%), A (12.5%) | O |
AB and AB | AB (50%), A (25%), B (25%) | O |
How Rh Factor Is Passed On
Rh is worked out separately and then combined with the ABO result. Being Rh-negative usually means having no working RHD gene, most often because the whole gene is missing⁴, so an Rh-negative parent can only pass on an Rh-negative copy.
Rh+ and Rh+: the child can be Rh+ or Rh−. The calculator gives 93.8% Rh+ and 6.3% Rh−.
Rh+ and Rh−: the child can be Rh+ or Rh−, 75% and 25% in the calculator.
Rh− and Rh−: the child can only be Rh−.
About 15% of white people, 8% of Black people and 1% of Asian people are Rh D-negative⁴. Rh also matters in pregnancy: problems can occur when a mother is Rh-negative and her fetus is Rh-positive, and treatment can be given to prevent them⁶. An ob-gyn can explain whether this applies to you.
Why the Percentages Are Estimates
A type A parent can be AA or AO, and a type B parent BB or BO, and a blood type alone cannot tell which¹. The calculator gives each option equal weight. In most populations, though, O is the most common ABO allele, so a type A or B parent is more often AO or BO than AA or BB, and the real chance of an O child is usually higher than the table shows. For example, under standard inheritance a type A parent whose own mother or father is type O must have inherited an O allele, so that parent is AO, and the real chance of an O child can be higher than the table shows.
Rare Exceptions
Standard inheritance explains almost every family, but not all. People with the Bombay phenotype inherit two inactive copies of the H gene, so they cannot make the H antigen that A and B antigens are built from, and their red cells carry no A or B antigen³. The cis-AB variant works the other way: a single allele can make both A and B antigens, which can explain results such as an O child born to an AB mother⁵.
Because exceptions like these exist, and because millions of unrelated people share each blood type, a blood type result can never confirm or rule out who a child's parent is.
Blood Type Chart: Parents to Child
Every ABO blood type a child could inherit from each pair of parent types.
| Parent 1 | Parent 2 | |||
|---|---|---|---|---|
| Type A | Type B | Type AB | Type O | |
| Type A | A, O | A, B, AB, O | A, B, AB | A, O |
| Type B | A, B, AB, O | B, O | A, B, AB | B, O |
| Type AB | A, B, AB | A, B, AB | A, B, AB | A, B |
| Type O | A, O | B, O | A, B | O |
Use the arrow keys to move between cells.
Rh factor is inherited separately: two Rh-negative parents can only have an Rh-negative child; any other pair can have an Rh-positive or Rh-negative child.
A Note on Accuracy
This shows possible outcomes based on standard inheritance patterns, not a guarantee, and cannot determine parentage. It should never be used or interpreted as a paternity test. Rare exceptions to standard ABO inheritance exist (e.g. the Bombay phenotype), this calculator covers the standard case, not every documented genetic exception.
Frequently Asked Questions
Can this calculator determine paternity?
No. This is a genetics education tool showing possible inherited blood types based on standard Mendelian inheritance. It cannot determine parentage and should never be used or interpreted as a paternity test.
Why does it show probabilities instead of one answer?
A parent's exact genotype often can't be determined from their blood type alone, type A could be genotype AA or AO, type B could be BB or BO¹, so the calculator shows the full range of possible offspring outcomes with their probabilities.
What does it mean if a blood type isn't listed as possible?
Some combinations are biologically impossible given the parents' types, for example, two type O parents cannot have a type A or B child, since type O carries no A or B allele to pass on.
Does this cover every genetic exception?
No. Rare exceptions to standard ABO inheritance exist, such as the Bombay phenotype. This calculator covers the standard case taught in genetics education, not every documented exception.
Sources
The ABO Blood Group, Dean, NCBI Bookshelf, 2005
Blood Types Tutorial: The Rh Factor, The Biology Project, University of Arizona, 1997
The ABO Blood Group, Dean, Blood Groups and Red Cell Antigens, NCBI Bookshelf, 2005
The Rh Blood Group, Dean, Blood Groups and Red Cell Antigens, NCBI Bookshelf, 2005
The Cis-AB Blood Group Phenotype: Fundamental Lessons in Glycobiology, Yazer, Olsson & Palcic, Transfusion Medicine Reviews, 2006
The Rh Factor: How It Can Affect Your Pregnancy, ACOG, 2024