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Blood Type Calculator

Health

Estimate the probability of a baby's ABO and Rh blood type from both parents' types, using standard Punnett square genetics. Not a substitute for lab testing.

Reviewed by the thecalcu.com team · Last updated July 25, 2026

Probability Type A

0.00%
Probability Type B
0.00%
Probability Type AB
0.00%
Probability Type O
100.00%
Probability Rh Positive
0.00%

This calculator computes your Probability Type A, Probability Type B, Probability Type AB, Probability Type O, Probability Rh Positive from the values you enter.

Inputs
Parent 1 Blood Type (ABO)Parent 2 Blood Type (ABO)Parent 1 Rh FactorParent 2 Rh Factor
Outputs
Probability Type AProbability Type BProbability Type ABProbability Type OProbability Rh Positive

What is a Baby Blood Type?

The Blood Type Calculator estimates the probability of a baby's ABO blood type and Rh factor from both parents' blood types, using standard Punnett square genetics. Unlike many other trait predictors, blood type follows well-understood single-gene inheritance, making this a more scientifically grounded estimate.

This is an educational and family curiosity tool, not a substitute for actual blood type testing. See also the Baby Eye Color Calculator for a related, though more simplified, genetics prediction tool.

Why Use a Blood Type Calculator?

Expecting parents are often curious about their baby's possible blood type, and because ABO and Rh genetics follow clear, well-established inheritance rules, this calculator can give a genuinely informative probability breakdown rather than just a rough guess.

Who Should Use This Calculator?

  • Expecting parents curious about their baby's possible blood type combinations.
  • Students learning genetics as a clear, real-world example of Punnett square inheritance.
  • Family members exploring how blood type can sometimes differ from what parents' own types might suggest.
  • Educators demonstrating dominant/recessive inheritance with a practical example.

What Insights Does the Blood Type Calculator Give You?

The calculator returns four ABO probabilities, Probability Type A, B, AB, and O, showing the full breakdown across possible outcomes. It also returns Probability Rh Positive, calculated independently since Rh factor is controlled by a separate gene from ABO type.

How to use this Baby Blood Type calculator

  1. Select Parent 1's blood type (ABO), A, B, AB, or O.
  2. Select Parent 2's blood type (ABO).
  3. Select each parent's Rh factor, Positive or Negative.
  4. Read the ABO probability breakdown and Rh Positive probability instantly.
  5. Remember this is a probability estimate, actual blood type is confirmed only through laboratory testing.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The calculator enumerates all possible hidden genotypes behind each parent's phenotype (e.g., type A could be AA or AO, weighted equally), then works through every possible allele combination in a Punnett square style calculation to determine the probability of each resulting ABO type. Rh factor is calculated the same way, independently, since it's controlled by a separate gene.

Worked example, Parent 1 is type A, Parent 2 is type O:

Parent 1 possible genotypes: AA (50%) or AO (50%). Parent 2: OO (100%).

Combining alleles: if Parent 1 is AA, child is always AO (type A). If Parent 1 is AO, child is 50% AO (type A) and 50% OO (type O).

Result: Type A ≈ 75%, Type O ≈ 25%, Type B ≈ 0%, Type AB ≈ 0%

Frequently Asked Questions

Can you really predict a baby's blood type from parents' blood types?
Blood type follows well-understood single-gene genetics (ABO and Rh systems), making this a more scientifically grounded prediction than many other trait predictors, though the exact probabilities depend on the parents' hidden genotypes, which this calculator estimates using a standard simplifying assumption.
Why does this calculator show a probability instead of one exact answer?
A parent with blood type A could genetically be AA or AO (since A is dominant over O), and without knowing which, the calculator assumes both possibilities are equally likely, this is why the result is a probability distribution rather than one certain answer.
How is the ABO probability calculated?
The calculator considers all possible hidden genotypes behind each parent's blood type (weighted equally when more than one is possible), then works through a Punnett square-style calculation across all possible allele combinations to determine the probability of each resulting blood type.
How is Rh factor calculated separately?
Rh factor follows the same dominant/recessive genetics pattern as ABO type, so it's calculated the same way, considering possible hidden genotypes behind each parent's Rh status and working through the allele combinations independently from the ABO calculation.
Why are ABO type and Rh factor calculated separately?
ABO blood type and Rh factor are controlled by different genes inherited independently of each other, so their probabilities are calculated separately and then combined (for example, A positive) to describe a complete blood type.
Can two parents with type O blood have a child with type A blood?
No, type O is genetically recessive (OO), so two type O parents can only pass O alleles to their child, always resulting in a type O child under standard ABO genetics.
Can two parents with type A blood have a child with type O blood?
Yes, if both parents carry a hidden O allele (genotype AO rather than AA), since each parent could pass either allele, there's a chance both pass their O allele, resulting in a type O child even though both parents appear as type A.
Is this calculator a substitute for actual blood type testing?
No, this calculator gives a probability estimate for educational and family curiosity purposes only. Confirming an actual blood type requires a laboratory blood test, not a genetics-based prediction.
What if a calculated blood type doesn't match what parents expect?
Unexpected results can arise from hidden heterozygous genotypes (like AO or BO) not reflected in a parent's own blood type, the calculator's probability distribution reflects exactly this kind of hidden genetic variation.
How does this relate to the Baby Eye Color Calculator?
Both are genetics-based prediction tools for expecting parents, but the [Baby Eye Color Calculator](/baby-eye-color-calculator/) uses a simplified approximation since eye color involves multiple genes, while this blood type calculator uses the more precise single-gene Punnett square approach appropriate for ABO and Rh genetics.
Also known as
baby blood type calculatorblood type genetics calculatorABO inheritance calculatorPunnett square blood type