Blood Type Calculator
HealthEstimate the probability of a baby's ABO and Rh blood type from both parents' blood types, using standard Punnett square genetics. Not a substitute for lab testing.
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%
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.
How to use this Baby Blood Type calculator
- Select Parent 1's blood type (ABO) — A, B, AB, or O.
- Select Parent 2's blood type (ABO).
- Select each parent's Rh factor — Positive or Negative.
- Read the ABO probability breakdown and Rh Positive probability instantly.
- Remember this is a probability estimate — actual blood type is confirmed only through laboratory testing.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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