About the Baby Eye Color Calculator
This baby eye color calculator estimates the probability that a child will have brown, green (including hazel) or blue (including grey) eyes. Choose each parent’s eye color and, if you know them, the grandparents’ eye colors — grandparents matter because a brown-eyed parent may silently carry a blue or green allele they inherited from their own mother or father.
It is a fun, genetics-based estimate for expecting parents, curious relatives and biology students learning about dominant and recessive traits. The results update the odds using simple probability (Bayes’ rule): for example, a brown-eyed parent with a blue-eyed parent of their own must carry a blue allele, which raises the chance of a light-eyed baby.
Real eye color is shaped by many genes (HERC2/OCA2 does most of the work, with a dozen or more others fine-tuning it), so any calculator is a simplification. This one uses the classic two-gene teaching model and assumes each allele is equally common in the population. Babies are often born with blue or grey eyes that darken over the first year, so final color usually settles by around age 1–3.
How to use the baby eye color calculator
- 1Choose Parent 1’s and Parent 2’s eye colors — hazel counts as green and grey as blue.
- 2If you know them, add each grandparent’s eye color; leave “Unknown” otherwise.
- 3Read the most likely eye color and the percentage for each color.
- 4Try different grandparent colors to see how a hidden recessive allele changes the odds.
Formula and method
The calculator uses the two-gene teaching model of eye color. At the first gene (bey2, on the HERC2/OCA2 region) the brown allele is dominant over blue; at the second (gey) the green allele is dominant over blue. Anyone with at least one brown allele has brown eyes; otherwise one or two green alleles give green/hazel eyes, and two blue alleles at both genes give blue eyes.
Each parent starts with Hardy–Weinberg genotype odds (every allele assumed equally common). If grandparents are given, their genotypes are conditioned on their eye colors and passed down with Mendelian 50/50 inheritance to form the parent’s odds, which are then conditioned on the parent’s own eye color (Bayes’ rule). Finally the two parents’ genotype odds are combined to give each possible child genotype, and those are grouped into eye colors.
- B / b
- Brown (dominant) and blue alleles at the bey2 gene
- G / g
- Green (dominant) and blue alleles at the gey gene
- Evidence
- The parent’s own eye color and any known grandparent colors
Worked examples
Brown-eyed and blue-eyed parents
A brown-eyed parent carries a hidden blue allele two times in three under the model, and passes it on half the time, so the baby has a 1 in 3 chance of not getting brown. That third is split evenly between green and blue: about 66.7% brown, 16.7% green, 16.7% blue.
Two brown-eyed parents, one has a blue-eyed mother
Parent 1 must carry a blue allele because their mother had blue eyes, so they pass it on half the time. Parent 2 is a carrier with probability 2/3 and passes it on a third of the time. The baby is non-brown with probability ½ × ⅓ = 1/6. Because the blue-eyed grandmother also passed Parent 1 a blue allele at the green gene, that sixth splits into about 10.4% green and 6.3% blue, leaving 83.3% brown.
Two blue-eyed parents
In the two-gene model two blue-eyed parents can only pass on blue alleles, so the prediction is 100% blue. In reality other genes make a darker-eyed child possible but uncommon.
Frequently asked questions
Can two blue-eyed parents have a brown-eyed baby?+
It is rare but possible. Simple dominant/recessive models say no, but eye color is influenced by many genes, so occasionally two blue-eyed parents have a child with green, hazel or even brown eyes.
Is brown eye color dominant?+
In the simplified model brown is dominant over green and blue, and green is dominant over blue. That is why brown-eyed parents can have blue-eyed children when both carry a hidden blue allele.
When do babies’ eyes change color?+
Many babies of European ancestry are born with blue or grey eyes. Pigment (melanin) builds up over the first 6–12 months, and most children’s eye color is settled by about age 1, though subtle changes can continue until around 3.
Why do grandparents’ eye colors matter?+
A brown-eyed parent might carry a blue or green allele without showing it. If one of their parents had blue eyes, they almost certainly carry one, which raises the odds that the baby will have lighter eyes.
How accurate is an eye color calculator?+
Treat it as an educational estimate. It captures the main pattern of inheritance but not every gene involved, and it assumes each allele is equally common, while real frequencies vary between populations.