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Blood Type Calculator

Predict baby's blood type from parents

Most Likely Blood Type

AB (56%)

Rh+

75%

Rh-

25%

Possible Child Blood Types

AB

56% chance

A

19% chance

B

19% chance

O

6% chance

Blood Type Probability

Type AB56%
Type A19%
Type B19%
Type O6%

Rh Factor Probability

Rh Positive (+)75%
Rh Negative (-)25%

Note: Rh+ parents can carry recessive Rh- genes

Example Calculations

1Parent A(Rh+) x Parent B(Rh+)

Inputs

Parent 1Type A, Rh+
Parent 2Type B, Rh+

Result

Most Likely Blood TypeAB (56% chance)
Type A chance19%
Type B chance19%
Type O chance6%
Rh+ probability75%
Rh- probability25%

Parent A has alleles [A, A, A, O] and Parent B has [B, B, B, O]. Out of 16 combinations: 9 produce AB, 3 produce A, 3 produce B, 1 produces O. Both Rh+ parents can carry recessive Rh-, giving 75% Rh+ and 25% Rh-.

2Parent O(Rh-) x Parent O(Rh+)

Inputs

Parent 1Type O, Rh-
Parent 2Type O, Rh+

Result

Child Blood TypeO (100% chance)
Impossible TypesA, B, AB
Rh+ probability50%
Rh- probability50%

Both Type O parents only carry O alleles [O, O], so all children will be Type O. One parent is Rh- (must be --) and one is Rh+ (could be +-), giving 50% chance of Rh+ and 50% Rh-.

Frequently Asked Questions

Q

How is blood type inherited?

Blood type is determined by genes inherited from both parents. Each parent contributes one allele. A and B are codominant, O is recessive. Type A can be AA or AO, Type B can be BB or BO, Type AB is AB, and Type O is OO.

  • Each person carries 2 alleles: one from each parent (e.g., AO, BO, AB, OO)
  • A and B are codominant – AB expresses both antigens on red blood cells
  • O is recessive – must receive O from both parents to be Type O
  • About 44% of the US population is Type O, 42% Type A, 10% Type B, 4% Type AB
Blood TypePossible GenotypesUS Population %
Type OOO only44%
Type AAA or AO42%
Type BBB or BO10%
Type ABAB only4%
Q

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

No. Two O blood type parents can only have O blood type children. Type O is recessive (OO genotype), so both parents can only pass O alleles.

  • Type O genotype is always OO – no hidden A or B alleles
  • Both parents contribute O, so every child receives OO
  • If a child of two O parents tests as A or B, paternity testing is warranted
  • Rare Bombay phenotype (h/h) can appear as Type O but carry A or B alleles
Q

Can AB parents have an O child?

No. An AB parent passes either A or B allele, never O. An O child requires both parents to pass O alleles, which an AB parent cannot do.

  • AB genotype has no O allele to pass to offspring
  • AB × AB parents can only produce A, B, or AB children
  • AB × O parents produce children who are either A or B (50/50)
  • The cis-AB variant (extremely rare) can occasionally produce unexpected results
Q

How does Rh factor inheritance work?

Rh+ is dominant over Rh-. Two Rh- parents always have Rh- children. Two Rh+ parents can have Rh- children if both are carriers (heterozygous).

  • About 85% of the population is Rh+ and 15% is Rh-
  • Rh+ can be homozygous (++) or heterozygous (+–)
  • Two Rh+ carriers (+–) have a 25% chance of an Rh– child
  • Rh– is most common in Caucasian populations (~17%) and rarest in Asian populations (~1%)
Q

What is Rh incompatibility?

If a Rh- mother carries a Rh+ baby, her body may produce antibodies against the baby's blood. This is managed with RhoGAM shots during pregnancy.

  • Affects ~15% of pregnancies where mother is Rh– and father is Rh+
  • RhoGAM injection given at 28 weeks and within 72 hours after delivery
  • First pregnancy is rarely affected – risk increases with subsequent pregnancies
  • Without treatment, hemolytic disease of the newborn can cause anemia and jaundice
  • RhoGAM costs $100–200 per injection and is covered by most insurance plans
Q

Can blood type prove paternity?

Blood type can only exclude paternity, not prove it. For example, if both parents are type O but the child is type A, the man is not the biological father. DNA testing is needed for definitive paternity.

  • Blood type can exclude about 30% of wrongly accused men
  • DNA paternity tests are 99.99% accurate and cost $100–500
  • Two Type A parents can have Type O children (if both carry AO genotype)
  • Court-admissible DNA tests require chain of custody and cost $300–500

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Last Updated: Mar 9, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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