Predict your child's possible blood types using ABO genetics and Rh factor inheritance. Includes compatibility chart, Rh incompatibility guide | Calculator4U
Predict possible blood types from parents.
The Blood Type Prediction Calculator uses the principles of Mendelian genetics to determine all possible blood types a child could inherit based on both parents' ABO blood types and Rh factors. Blood type is one of the most reliably inherited biological traits—governed by a straightforward dominance relationship between three alleles (A, B, and O) at a single gene locus, plus a separate dominant-recessive Rh factor—making prediction highly accurate once both parents' types are known.
Understanding blood type genetics has practical applications beyond curiosity. It is critical for pregnancy planning (where Rh incompatibility can cause serious complications), blood transfusions, and clinical health assessments. Each person carries two ABO alleles, inheriting one from each parent. The blood type expressed depends entirely on which alleles dominate.
The dominance hierarchy works as follows: A and B alleles are codominant (both expressed equally when paired together, producing type AB), while O is recessive to both A and B (only expressed when two O alleles are present). The practical result: Type A blood can conceal a hidden O allele (genotype AO), Type B can conceal a hidden O allele (genotype BO), but Type O always means OO and Type AB always means exactly one A and one B. This hidden recessive O allele is why two type-A parents can produce an O-type child—both parents were secretly carrying the AO genotype.
The Rh factor (positive or negative) follows similar dominant-recessive rules. Rh+ is dominant over Rh-, so a person with even one positive allele will test as Rh+. While two Rh+ parents can potentially have an Rh- child if both carry a hidden recessive negative allele, two Rh- parents can only pass on negative alleles, meaning they will only have Rh- children.
A and B are codominant; O is strictly recessive to both A and B.
| Parent 1 | Parent 2 | Possible Child Types |
|---|---|---|
| A | A | A, O |
| A | B | A, B, AB, O |
| A | O | A, O |
| B | B | B, O |
| B | O | B, O |
| AB | AB | A, B, AB |
| AB | O | A, B |
| O | O | O only |
Parents: Type A × Type B. Both individuals could dynamically pass down hidden alleles if they are AO and BO genotypes. Because of this, their potential pregnancy outcomes could yield any of the four major blood groups: Type A (inheriting AO), Type B (inheriting BO), Type AB (inheriting A from one, B from the other), or Type O (inheriting the recessive O from each parent).
| Mother Rh Status | Father Rh Status | Possible Child Rh | Incompatibility Risk? |
|---|---|---|---|
| Rh+ | Rh+ | Rh+ or Rh- | No risk |
| Rh+ | Rh- | Rh+ or Rh- | No risk |
| Rh- | Rh- | Rh- only | No risk |
| Rh- | Rh+ | Rh+ or Rh- | ⚠️ Potential — consult OB/GYN |
Rh incompatibility only poses a risk when an Rh-negative mother carries an Rh-positive baby (inherited from an Rh-positive father). The mother's immune system may recognize the Rh protein as foreign and develop antibodies against the baby's blood cells. While typically harmless during a first pregnancy, it can cause hemolytic disease of the newborn (HDN) in subsequent pregnancies. The RhoGAM injection, given at 28 weeks and within 72 hours of delivery, prevents this sensitization and has successfully reduced HDN cases by over 98% since 1968.
| Blood Type | % of US Population | Can Donate Red Cells To | Can Receive From |
|---|---|---|---|
| O+ | 37.4% | O+, A+, B+, AB+ | O+, O- |
| O- | 6.6% | All blood types (universal donor) | O- only |
| A+ | 35.7% | A+, AB+ | A+, A-, O+, O- |
| A- | 6.3% | A+, A-, AB+, AB- | A-, O- |
| B+ | 8.5% | B+, AB+ | B+, B-, O+, O- |
| B- | 1.5% | B+, B-, AB+, AB- | B-, O- |
| AB+ | 3.4% | AB+ only | All blood types (universal recipient) |
| AB- | 0.6% | AB+, AB- | AB-, A-, B-, O- |
Source: American Red Cross / Stanford Blood Center. O- is the universal red cell donor; AB+ is the universal recipient. AB- is the rarest blood type at 0.6% of the US population.
Blood type is inherited through Mendelian genetics — each parent passes one of their two ABO alleles (A, B, or O) to the child, and the combination determines the child's blood type. A and B alleles are codominant (both expressed, producing type AB when paired), while O is recessive to both (only expressed as type O when two O alleles are inherited). Type A blood can carry a hidden O allele (genotype AO); Type B can carry BO; Type AB is always exactly one A plus one B; Type O is always OO. The Rh factor (+ or −) is inherited separately, with Rh+ dominant over Rh−.
No — two O blood type parents can only have O blood type children. Type O requires the OO genotype, meaning O parents carry only O alleles and can only pass O to their children. Every child will be OO (type O). If a child born to two O-type parents tests as A, B, or AB, the explanation is either a laboratory error, an extremely rare genetic mutation at the ABO locus, a blood chimera condition (very rare), or a question about biological parentage. This principle is so reliable it has been used as evidence in paternity disputes for over a century.
An AB child requires inheriting one A allele from one parent and one B allele from the other. Parent combinations that can produce an AB child: A×B (if A parent carries AO and B parent carries BO, both A and B alleles can be passed), AB×A, AB×B, AB×AB. Combinations that cannot produce AB: O×O, A×O, B×O, AB×O (this produces A and B children but not AB — the AB parent's O from the other parent pairs with the O to make an A or B child, never AB). AB×O can never produce an O child either.
Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby (possible when the father is Rh-positive). During delivery, miscarriage, or procedures like amniocentesis, fetal blood can enter the mother's circulation, causing her immune system to develop anti-Rh antibodies. These antibodies pose no risk in the first affected pregnancy but in subsequent Rh-positive pregnancies they cross the placenta and attack fetal red blood cells — causing hemolytic disease of the newborn (HDN), which ranges from mild anemia to severe complications. Prevention is nearly 100% effective: Rh-negative pregnant women receive a RhoGAM injection at 28 weeks gestation and within 72 hours of any delivery, miscarriage, or invasive procedure. RhoGAM has reduced HDN incidence by over 98% since its introduction in the US in 1968. All Rh-negative women who are pregnant or planning pregnancy should confirm this protocol with their OB/GYN.
O-negative (O−) is the universal red blood cell donor — it can be transfused to any patient regardless of blood type, making it the default used in emergency situations before a patient's blood type is confirmed. Only 6.6% of the US population has O− blood, making it chronically in short supply. AB-positive (AB+) is the universal recipient for red blood cells — AB+ individuals can receive red cells from any blood type. AB blood plasma (regardless of Rh factor) is the universal plasma donor — used in trauma centers. O+ is the most common blood type at 37.4% of the US population and can be transfused to any Rh-positive recipient. The American Red Cross reports that someone in the US needs blood every 2 seconds — knowing your blood type and donating if eligible is a direct lifesaving action.
Yes — ABO blood type distribution varies significantly by ethnicity and geographic ancestry. Type O is most prevalent in Native American and Indigenous populations (nearly 100% in some groups), Central and South American populations (70–80%), and African populations (50–60%). Type A is most prevalent in European populations (40–45%), particularly Scandinavian and Eastern European. Type B is most common in Asian and South Asian populations (25–30%). Type AB is rare across all populations, highest in parts of Japan and Korea at 10–11%. In the US overall, O+ is most common (37.4%), followed by A+ (35.7%), with AB− the rarest at just 0.6%. These distributions reflect ancient population migrations, genetic bottlenecks, and possibly disease resistance advantages in specific environments.
Blood type does not meaningfully affect personality or determine compatible romantic partners, despite persistent cultural beliefs — particularly in Japan and South Korea where "blood type personality" theory (ketsueki-gata) remains popular. Multiple large-scale studies including a 2014 Japanese study of 10,000+ participants found no significant personality differences by blood type. The "blood type diet" (popularized by Dr. Peter J. D'Adamo in 1996) has no credible scientific backing — a 2013 systematic review in the American Journal of Clinical Nutrition found no evidence that blood type diets produce health benefits. Blood type does have legitimate medical relevance: it determines transfusion compatibility, influences Rh pregnancy risk, and some studies suggest modest associations between blood types and susceptibility to certain infections (O types show some resistance to severe malaria; A types may have slightly higher COVID-19 clotting risk). These associations are real but modest — blood type is not destiny.