Blood Type Inheritance Calculator (ABO/Rh)
Find out what blood types your children could inherit. Enter both parents' ABO genotype and Rh factor to see probabilities (A, B, AB, O, +/−).
CalcVita. (2026). Blood Type Inheritance Calculator (ABO/Rh). CalcVita. Retrieved July 3, 2026, from https://calcvita.com/en/calculators/blood-type-inheritance
How to use the blood type inheritance calculator
Select the ABO genotype and Rh factor genotype for each parent. The calculator uses the Punnett square method to compute the exact probability of each possible blood type in your children. For blood types A and B, the genotype matters: AA or AO give different results. For AB and O, only one genotype is possible.
ABO blood type genetics
ABO blood type is determined by three alleles: I^A (A antigen), I^B (B antigen), and i (no antigen). I^A and I^B are codominant; i is recessive. Genotypes: AA or AO → type A; BB or BO → type B; AB → type AB; OO → type O. The ABO gene is located on chromosome 9.
Rh factor genetics
The Rh (RhD) factor is controlled by the RHD gene on chromosome 1. DD = homozygous Rh+; Dd = heterozygous Rh+ (carrier of one Rh− allele); dd = Rh−. ABO and Rh genes are on different chromosomes, so they are inherited independently (independent assortment).
Why genotype matters for ABO
Two parents with blood type A could each be AA or AO. Their children's blood types depend on which combination is true: AA × AA → 100% A; AA × AO → 100% A; AO × AO → 75% A, 25% O; AO × OO → 50% A, 50% O. Knowing the genotype gives exact predictions instead of ranges.
Scientific References
- Dean L. (2005). Blood Groups and Red Cell Antigens. Chapter 2: Blood group antigens are surface markers on the red blood cell membrane. NCBI Bookshelf NBK2261. National Center for Biotechnology Information.
- Landsteiner K. (1900). Zur Kenntnis der antifermentativen, lytischen und agglutinierenden Wirkungen des Blutserums und der Lymphe. Zentralbl Bakteriol 27:357–362.
- Landsteiner K. (1901). Über Agglutinationserscheinungen normalen menschlichen Blutes. Wien Klin Wochenschr 14:1132–1134. (Nobel Prize work, 1930)
- Landsteiner K, Wiener AS. (1940). An agglutinable factor in human blood recognized by immune sera for rhesus blood. Proc Soc Exp Biol Med 43:223–224.
- Yamamoto F, Clausen H, White T, Marken J, Hakomori S. (1990). Molecular genetic basis of the histo-blood group ABO system. Nature 345(6272):229–233. PMID: 2333095
- Wagner FF, Flegel WA. (2000). RHD gene deletion occurred in the Rhesus box. Blood 95(12):3662–3668. PMID: 10845898
- How is ABO blood type inherited?
- ABO blood type is determined by the ABO gene, which has three main alleles: I^A (produces A antigen), I^B (produces B antigen), and i (produces no antigen). Each person inherits one allele from each parent. I^A and I^B are codominant, meaning both are expressed equally in AB individuals. The i allele is recessive — only people with two copies (ii genotype) have blood type O. This is why two type-A parents who are both carriers of i can have a type-O child.
- What does ABO genotype mean?
- Your ABO blood type phenotype (A, B, AB, or O) is what shows on a blood test. Your genotype is the actual pair of alleles you carry: type A can be AA (homozygous) or AO (heterozygous), type B can be BB or BO, type AB is always AB, and type O is always OO. The genotype determines which blood types you can pass to your children. If you don't know your exact genotype, consider having a genetic test or asking about your family's blood type history.
- How is the Rh factor inherited?
- The Rh factor (RhD antigen) is controlled by the RHD gene. Having at least one D allele makes you Rh positive (Rh+); having two d alleles makes you Rh negative (Rh−). Like ABO, Rh inheritance follows Mendelian genetics. Two Rh+ parents who are both heterozygous (Dd × Dd) have a 25% chance of an Rh− child. An Rh+ parent (DD) crossed with Rh− (dd) always produces Rh+ children. Two Rh− parents (dd × dd) will always have Rh− children.
- Can two O blood type parents have an A or B child?
- No. Type-O parents have the genotype OO (two recessive i alleles). They can only pass an i allele to their children, so all children will also be OO (type O). If a child of two type-O parents has type A or B blood, this may indicate a testing error, a very rare mutation, or non-paternity. This is one reason blood type alone cannot definitively establish parentage.
- What is an Rh-incompatible pregnancy?
- Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby (which can happen if the father is Rh+). The mother's immune system may produce anti-D antibodies that can cross the placenta and destroy fetal red blood cells — a condition called hemolytic disease of the newborn (HDN). The first pregnancy is usually unaffected since sensitization occurs at delivery. Subsequent Rh-positive pregnancies carry higher risk. Rh immunoglobulin (RhoGAM) given to the mother prevents sensitization and is a routine part of prenatal care.
- Why can't this calculator give exact percentages for all parents?
- Exact probabilities depend on the parents' genotypes, not just their phenotypes. For blood type A, the parent could be AA (homozygous) or AO (heterozygous) — these give different probabilities for children. This calculator asks you to specify the genotype (AA vs. AO, BB vs. BO) so it can compute exact Punnett square probabilities. If you don't know your genotype, a DNA or genetic test can clarify it, or you can estimate based on your family's blood type history.
Suggested article
Blood Type Inheritance: How ABO and Rh Factor Are Passed to Your Children
Your blood type is determined by the ABO gene and the Rh factor — two independent genetic systems. Understanding how they're inherited helps predict which blood types your children may have using the Punnett square method.
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