Chances of blue/gray, green/hazel or brown eyes from the parents’ eye colors, using published data on the HERC2 gene variant that matters most, with its limits spelled out
How Eye Color Is Inherited
School charts often treat brown as dominant and blue as recessive, like a Punnett square with one gene. That is a useful first approximation, but eye color is polygenic. The biggest single influence is a variant in the HERC2 gene, rs12913832, which controls how much the neighbouring OCA2 gene is switched on in the iris. Sturm and colleagues found that this one variant predicted eye color better than anything they had tested before, and that the blue-associated allele lowers OCA2 activity. The IrisPlex forensic test uses six such variants and reports over 90% accuracy for blue and brown, but intermediate colors such as green and hazel remain the hardest to predict.
What the Data Show
Sturm et al. (2008) recorded genotype and eye color for 3,168 adolescent twins and siblings, mostly of northern European origin. Summed over a second, modifying variant (OCA2 R419Q):
Even two copies of the blue-associated allele give green or hazel eyes in about a quarter of people, and one copy splits between green/hazel and brown. That is why a single-gene chart can’t give certainty.
How the Calculator Works
- From a parent’s eye color, it estimates their likely genotype using the table (for example, most blue-eyed people in the study were C/C).
- Each parent passes one copy at random, so the chance of passing the blue-associated allele is P(C/C) + ½ P(C/T).
- Combine the two parents for the child’s genotype, then apply the table’s color shares for each genotype.
- If a parent knows their genotype from a DNA test, choose it to replace step 1.
Results for Every Parent Combination
Two brown-eyed parents still have about a 1-in-6 chance of a blue-eyed child in this model, because many brown-eyed people carry one blue-associated copy. To see the one-gene version of the same idea, try the Punnett square calculator with Bb × Bb.
Common Mistakes
- Treating a chart as a prediction. These are population averages from one study, not a forecast for a particular baby.
- Assuming two blue-eyed parents can’t have a brown-eyed child. It is rare (about 4% here) but other genes make it possible.
- Judging too early. The American Academy of Pediatrics’ HealthyChildren.org says it takes about a year for the pigment cells to finish their work, so a newborn’s eye color is not final.
- Applying the numbers everywhere. The data come from people of mainly northern European ancestry; in populations where brown eyes are almost universal, the odds are very different.
What This Calculator Does Not Cover
It uses one gene variant and three color groups. It does not model the other known eye-color genes, gray versus blue, eye-color changes in childhood, or conditions such as albinism and heterochromia (a baby with one brown and one blue eye should be checked by a doctor, HealthyChildren.org advises). A child’s eye color is not evidence of parentage.
Frequently Asked Questions
Can two blue-eyed parents have a brown-eyed baby?
Yes, though it is uncommon. In this model, based on Sturm et al. (2008), about 4% of children of two blue-eyed parents have brown eyes, because eye color depends on more than one gene.
Is brown eye color dominant?
Roughly. The brown-associated version of the HERC2 variant usually wins, but eye color is polygenic, so the simple dominant/recessive picture is an approximation.
What gene controls eye color?
Mostly OCA2, switched on or off by a variant in the neighbouring HERC2 gene (rs12913832). Several other genes adjust the shade.
What are the chances of a blue-eyed baby with one brown-eyed and one blue-eyed parent?
About 33% in this model, with about 33% green/hazel and 34% brown.
When do babies’ eyes change color?
Mostly in the first year. HealthyChildren.org (American Academy of Pediatrics) says change slows after about 6 months, but final color isn’t reliable to call before the first birthday.
Can a DNA test predict eye color?
Better than parents’ colors alone. Forensic tests like IrisPlex use six variants and report over 90% accuracy for blue and brown, but green and hazel are harder.
How to Use This Calculator
- Choose each parent’s eye color — brown, blue or gray, or green or hazel.
- Add genotypes if you know them — from a consumer DNA test reporting rs12913832; otherwise leave Unknown.
- Calculate — the chance of blue/gray, green/hazel and brown eyes.
- Read the caveats — the result is an estimate from one gene in one population.
📚 Sources & References- [1] Sturm RA, Duffy DL, Zhao ZZ, et al. A single SNP in an evolutionary conserved region within intron 86 of the HERC2 gene determines human blue-brown eye color. Am J Hum Genet 2008;82(2):424-431 (via PubMed, PMID 18252222). doi.org
- [2] Walsh S, Liu F, Ballantyne KN, et al. IrisPlex: a sensitive DNA tool for accurate prediction of blue and brown eye colour in the absence of ancestry information. Forensic Sci Int Genet 2011;5(3):170-180 (via PubMed, PMID 20457092). doi.org
- [3] Sturm et al. 2008, full text with Table 4, PubMed Central PMC2427173 (accessed October 2026). pmc.ncbi.nlm.nih.gov
- [4] HealthyChildren.org (American Academy of Pediatrics). David Hill, MD. What Color Will My Baby’s Eyes Be? (updated July 29, 2021). www.healthychildren.org
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Editorial Standards — Every calculator is built from peer-reviewed formulas and official data sources, editorially reviewed for accuracy, and updated regularly.
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