Blood Type Calculator - Predict Your Child’s Blood Type

Our free blood type calculator helps you predict the possible blood types of your child based on the blood types of both parents. Using established genetics principles, this tool shows all possible combinations and their likelihood based on ABO and Rh inheritance patterns.

What is Blood Type?

Blood type (also called blood group) is a classification of blood based on the presence or absence of specific antigens on the surface of red blood cells. The two most important blood group systems are:

1. ABO system: Determines if you have A, B, AB, or O blood type
2. Rh system: Determines if you are Rh positive (+) or Rh negative (-)

Together, these create eight main blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-.

How Blood Type is Inherited

Blood type is determined by genes inherited from both parents. Each parent passes one of two ABO genes and one of two Rh genes to their child.

ABO Genes:

• A gene (IA): Dominant, produces A antigen
• B gene (IB): Dominant, produces B antigen
• O gene (i): Recessive, produces no antigen

Rh Genes:

• Positive (+): Dominant
• Negative (-): Recessive

Understanding Blood Type Genetics

ABO Blood Type Inheritance

Parent 1	Parent 2	Possible Child Blood Types
O × O		O only
O × A		O or A
O × B		O or B
O × AB		A or B (never O or AB)
A × A		O or A
A × B		O, A, B, or AB (all types possible)
A × AB		A, B, or AB (never O)
B × B		O or B
B × AB		A, B, or AB (never O)
AB × AB		A, B, or AB (never O)

Genotype vs Phenotype

Genotype is the actual genetic makeup (the genes you carry), while Phenotype is the observable trait (your blood type).

Possible Genotypes:

• Type A: AA or AO
• Type B: BB or BO
• Type AB: AB only
• Type O: OO only

Rh Factor Inheritance

The Rh factor follows simple dominant-recessive inheritance:

Parent 1 Rh	Parent 2 Rh	Child Rh+ Probability	Child Rh- Probability
+ × +		75-100%	0-25%
+ × -		50-100%	0-50%
- × -		0%	100%

Note: If both parents are Rh+, they can still have an Rh- child if both carry the recessive negative gene.

The Eight Main Blood Types

Type A (A+ and A-)

• Frequency: 34% of US population (A+), 6% (A-)
• Antigens: A antigens on red blood cells
• Antibodies: Anti-B antibodies in plasma
• Can donate to: A+, A-, AB+, AB- (A- is universal for A and AB recipients)
• Can receive from: A+, A-, O+, O- (A+ can also receive from A+ and O+)

Type B (B+ and B-)

• Frequency: 9% of US population (B+), 2% (B-)
• Antigens: B antigens on red blood cells
• Antibodies: Anti-A antibodies in plasma
• Can donate to: B+, B-, AB+, AB-
• Can receive from: B+, B-, O+, O-

Type AB (AB+ and AB-)

• Frequency: 3% of US population (AB+), 1% (AB-)
• Antigens: Both A and B antigens
• Antibodies: No anti-A or anti-B antibodies
• Can donate to: AB+ (AB+ only for AB+), AB- (AB types only)
• Can receive from: All blood types (AB+ is universal recipient)

Type O (O+ and O-)

• Frequency: 38% of US population (O+), 7% (O-)
• Antigens: No A or B antigens
• Antibodies: Both anti-A and anti-B antibodies
• Can donate to: All blood types (O- is universal donor)
• Can receive from: O+ and O- only

Blood Type Distribution by Ethnicity

Blood type frequencies vary significantly among different ethnic groups:

United States (Overall)

Blood Type	Percentage
O+	38%
O-	7%
A+	34%
A-	6%
B+	9%
B-	2%
AB+	3%
AB-	1%

By Ethnic Group

Caucasian:

• O+ (37%), A+ (33%), B+ (9%), AB+ (3%)
• O- (8%), A- (7%), B- (2%), AB- (1%)

African American:

• O+ (47%), A+ (24%), B+ (18%), AB+ (4%)
• O- (4%), A- (2%), B- (1%), AB- (<1%)

Hispanic:

• O+ (53%), A+ (29%), B+ (9%), AB+ (2%)
• O- (4%), A- (2%), B- (1%), AB- (<1%)

Asian:

• O+ (39%), A+ (27%), B+ (25%), AB+ (7%)
• O- (<1%), A- (<1%), B- (<1%), AB- (<1%)

Blood Type and Health Associations

Research has found correlations between blood type and certain health conditions:

Type A

Higher risk for:

• Stomach cancer
• Cardiovascular disease
• Type 2 diabetes
• Stress-related conditions

Lower risk for:

• Malaria
• Pancreatic cancer

Type B

Higher risk for:

• Pancreatic cancer
• Ovarian cancer
• Memory problems

Lower risk for:

• Heart disease
• Stomach cancer

Type AB

Higher risk for:

• Blood clots
• Stroke
• Heart disease
• Memory loss and cognitive impairment

Lower risk for:

• High blood pressure during pregnancy

Type O

Higher risk for:

• Peptic ulcers
• Cholera
• Plague
• Bleeding disorders

Lower risk for:

• Heart disease
• Blood clots
• Stroke
• Pancreatic cancer
• Stomach cancer

Note: Blood type is just one of many factors influencing health. Lifestyle, diet, genetics, and environment play much larger roles.

Blood Type Compatibility

Blood Donation Compatibility

Understanding compatibility is crucial for safe blood transfusions:

Universal Donor: O- (can donate red blood cells to anyone) Universal Recipient: AB+ (can receive red blood cells from anyone)

Complete Compatibility Chart

Recipient	Can Receive From
O-	O- only
O+	O-, O+
A-	O-, A-
A+	O-, O+, A-, A+
B-	O-, B-
B+	O-, O+, B-, B+
AB-	O-, A-, B-, AB-
AB+	All blood types

Plasma Donation Compatibility

Plasma compatibility is the reverse of red blood cell compatibility:

Universal Plasma Donor: AB (can donate plasma to anyone) Universal Plasma Recipient: O (can receive plasma from anyone)

Rh Factor and Pregnancy

Rh Incompatibility

Rh incompatibility occurs when an Rh- mother carries an Rh+ baby (inherited from Rh+ father):

First Pregnancy:

• Usually no problems
• Mother may develop anti-Rh antibodies during delivery

Subsequent Pregnancies:

• Antibodies can attack Rh+ babies
• Can cause hemolytic disease of the newborn (HDN)
• Symptoms: anemia, jaundice, brain damage

Prevention: RhoGAM

RhoGAM (Rh immunoglobulin) prevents Rh sensitization:

• Given at 28 weeks of pregnancy
• Given within 72 hours after delivery of Rh+ baby
• Also given after miscarriage, abortion, or amniocentesis
• Highly effective (prevents sensitization in 99% of cases)

When RhoGAM is Needed

Mother	Father	Baby	RhoGAM Needed?
Rh-	Rh+	Rh+	Yes
Rh-	Rh+	Rh-	No
Rh-	Rh-	Rh-	No
Rh+	Any	Any	No

Rare Blood Types

Some blood types are extremely rare:

Rh-null (Golden Blood)

• Rarest blood type in the world
• Lacks all Rh antigens
• Fewer than 50 people worldwide
• Can donate to anyone with rare blood types
• Can only receive from other Rh-null donors

Other Rare Types

• A- Bombay: Less than 0.0001% of population
• B- Bombay: Extremely rare
• AB-: Only 1% of US population
• Duffy-null: Common in people of African descent (up to 70%)

Blood Type Myths and Facts

Myth: Blood Type Determines Personality

Reality: The blood type personality theory (popular in Japan and Korea) has no scientific basis. Personality is shaped by genetics, environment, and experiences - not blood antigens.

Myth: You Should Eat Based on Your Blood Type

Reality: The “Blood Type Diet” lacks scientific evidence. No peer-reviewed studies support the claim that blood type should dictate dietary choices. Balanced nutrition is important for everyone regardless of blood type.

Myth: O- is the Rarest Blood Type

Reality: While O- is the universal donor, AB- is actually rarer (1% vs 7% of US population). Rh-null is the true rarest blood type worldwide.

Myth: Blood Type Can’t Change

Reality: While extremely rare, blood type can change after:

• Bone marrow or stem cell transplant
• Certain cancers or infections
• Rare medical conditions

How to Find Your Blood Type

Medical Testing

1. Blood donation: Free and helps others
2. Doctor’s office: Request during routine blood work
3. Home testing kits: Available online ($10-30)
4. Hospital records: Check previous medical records

Home Blood Type Test

Home testing kits typically include:

• Lancet for finger prick
• Test card with antibodies
• Instructions
• Results in 5-10 minutes

Accuracy: 95-99% when done correctly

Why Knowing Matters

• Emergency situations requiring blood transfusions
• Pregnancy planning (Rh factor considerations)
• Blood or organ donation
• Medical procedures or surgeries
• Family genealogy and genetics research

Frequently Asked Questions

Can two parents with type O have a child with type A or B?

No, this is genetically impossible. Two type O parents (genotype OO) can only pass O genes to their children, resulting in only type O children. If this occurs, non-paternity or a genetic mutation may be involved.

Can two parents with type A have a child with type O?

Yes, if both parents have genotype AO (not AA). Each parent would pass the O gene to the child, resulting in genotype OO (type O).

What is the rarest blood type?

Rh-null (golden blood) is the rarest, found in fewer than 50 people worldwide. Among common types, AB- is the rarest in the US population at approximately 1%.

Is O negative really the universal donor?

Yes, for red blood cell transfusions. O- blood lacks A, B, and Rh antigens, so it won’t trigger an immune response in recipients. However, for plasma transfusions, AB is the universal donor.

Can blood type change over time?

Normally, no. Blood type is determined by genes and remains constant throughout life. The only exceptions are bone marrow/stem cell transplants, where you may adopt the donor’s blood type, or extremely rare medical conditions.

Why is Rh negative less common?

The Rh- factor is recessive and requires two copies of the negative gene. The Rh+ allele is dominant and more common in most populations. Rh- frequency varies by ethnicity (highest in Basque people at 30-35%, lowest in Asians at <1%).

Do siblings always have the same blood type?

No. Siblings can have different blood types because each parent passes one of their two genes randomly to each child. Siblings share 50% of their DNA on average but can inherit different combinations of ABO and Rh genes.

Can you determine paternity with blood type?

Blood type can only exclude paternity, not confirm it. For example, if the mother is type O and the child is type AB, a man with type O cannot be the father. However, DNA testing is required for definitive paternity determination.

Conclusion

Understanding blood type genetics helps you predict your child’s possible blood types and appreciate the complexity of human heredity. This free blood type calculator provides quick estimates based on parental blood types using established genetic principles.

Remember that blood typing requires actual laboratory testing for medical accuracy. The calculator shows theoretical possibilities based on genetics but cannot account for rare genetic variations or mutations.

If you’re pregnant or planning to become pregnant, discuss Rh factor compatibility with your healthcare provider to ensure proper prenatal care.

Knowing your blood type and your family’s blood types can be valuable for medical emergencies, blood donation, and understanding your genetic heritage. Consider donating blood regularly - you could save a life!

Find your local blood donation center:

• American Red Cross: redcrossblood.org
• America’s Blood Centers: americasblood.org

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Medical Disclaimer: This calculator is for educational and informational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Blood type predictions are based on theoretical genetics and may not account for rare genetic variations. Always consult with healthcare professionals for medical decisions, especially regarding pregnancy and Rh compatibility. Actual blood typing requires laboratory testing.