Eye Color Gene Calculator

What colour eyes will a baby have? This calculator estimates the odds for brown, blue, green and hazel eyes from both parents’ eye colours, and if you know each parent’s genotype (BB, Bb or bb) it runs that exact cross instead and draws the Punnett square. One honest note before you start: real eye colour is shaped by many genes working together, mainly OCA2 and HERC2. This is a simplified one-gene teaching model, so treat the percentages as an illustration of how inheritance odds work, not as a genetic prediction.

Quick Answer

How to use the eye color gene calculator

Choose each parent's eye colour, add genotypes only if you genuinely know them, then click Predict Eye Color. Results stay hidden until you do.

1. Pick both eye colours: brown, blue, green or hazel for each parent. On its own, this runs colour mode.
2. Add genotypes if known: BB, Bb or bb for each parent. Genotype mode switches on only when both are set. If one is left on Unknown, the tool quietly uses the colours instead, and the result panel tells you which mode ran.
3. Read the bars: each bar is one colour's share, shown to one decimal place. Colours at 0% get no bar. The most likely colour is named underneath.
4. Check the Punnett square: in genotype mode it shows all four allele pairings, tinted amber when the pairing carries a B allele and blue when it is bb.

Exactly what model this calculator runs

It runs two lookups, not a genetic simulation. Knowing which one produced your result is the difference between reading the page honestly and over-trusting it.

Genotype mode. There are only five distinct outcomes across all nine crosses. Any cross involving a BB parent returns 100% brown. Bb by Bb returns 75% brown, 18.75% blue and 6.25% green. Bb by bb returns 50% brown, 37.5% blue and 12.5% green. bb by bb returns 75% blue and 25% green. Hazel is always zero in this mode, because the model's bb outcomes are split between blue and green only. The split itself is a modelling choice baked into the tool: a strict classroom Punnett square would call every bb child one colour, while this tool divides bb children 75/25 or 50/25 between blue and green depending on the cross.

Colour mode. With genotypes unknown, the tool reads a fixed table for the colour pairing, printed in full further down this page. Brown pairings lean brown, blue pairings lean blue, and green sits between them, following the classroom dominance ladder: brown over green and blue, green over blue. Hazel breaks the ladder. Any pairing that includes a hazel-eyed parent, including hazel with hazel, returns the same 35% brown, 10% blue, 25% green and 30% hazel split. That flat treatment is the crudest part of the model, and it is disclosed here because the table below makes it obvious anyway.

Worked example: Bb brown-eyed parent by bb blue-eyed parent

Set Parent 1 to Brown with genotype Bb and Parent 2 to Blue with genotype bb, exactly as the calculator is pre-filled, and click Predict Eye Color.

Each parent passes one allele at a time. The four equally likely pairings are Bb, Bb, bb and bb, so half the children in the model are Bb and half are bb. The tool maps Bb children to brown and splits the bb half between blue and green in a 75/25 ratio, which gives Brown 50.0%, Blue 37.5%, Green 12.5%, most likely Brown. The Punnett square under the bars shows the four pairings, with the two Bb cells tinted amber and the two bb cells tinted blue.

Each row is a real run of this calculator, displayed the way the tool displays it, to one decimal place. Note the display rounding: the stored 18.75% and 6.25% in the Bb by Bb cross appear as 18.8% and 6.3%.

Full parent-pair probability table (colour mode)

These are the exact percentages the calculator returns in colour mode, with both genotypes set to Unknown. The order of the parents does not matter.

Read the hazel rows carefully: they are identical by design in this tool, not a copying error in the table. If your pairing involves hazel, the model has nothing more specific to say, which is one more reason to treat colour mode as a rough illustration.

Why real eye colour genetics is more complicated

Real eye colour is polygenic, and the one-gene ladder used here is a classroom simplification of a much richer system. The U.S. National Library of Medicine's MedlinePlus Genetics primer, Is eye color determined by genetics?, explains that most eye-colour genes control the production, transport or storage of melanin, the pigment in the front layers of the iris. Brown eyes carry a large amount of melanin there; blue eyes carry very little.

Two neighbouring genes on chromosome 15 do most of the work. OCA2 produces the P protein, which helps melanosomes mature and store melanin. A regulatory segment inside HERC2, around the variant rs12913832, switches OCA2 up or down, and that single switch is the strongest known predictor of blue versus brown eyes. It is still not the whole story: MedlinePlus lists ASIP, IRF4, SLC24A4, SLC24A5, SLC45A2, TPCN2, TYR and TYRP1 as further contributors, and research cohorts keep finding smaller modifiers around the main switch.

That is why the exceptions exist. Two blue-eyed parents can, rarely, have a brown-eyed child, because other genes can restore enough melanin production even when the main switch points to blue. Eye colour also sits on a continuum rather than in four tidy boxes, and it can shift in infancy as melanin builds up. If you want the general probability ideas behind crosses like these, our compound probability calculator combines independent events step by step, the coin flip probability calculator covers the same 50/50 logic as a single allele draw, and the conditional probability calculator shows how odds change once part of the outcome is known.

Disclaimer: This tool illustrates a simplified one-gene model of eye colour inheritance for educational purposes. Real eye colour is polygenic and influenced by many genes plus developmental factors. Results are not medical advice and cannot predict, diagnose or confirm anything about a real child.

What other calculators miss

Most baby eye colour tools ask for two colours, return a chart, and present it with more confidence than the science supports. The review behind this page found the same gaps repeatedly:

• Colour-only tools with no genotype route (CareForCuties and similar chart pages): helpful grandparent discussion, but the calculator itself never lets you enter a known genotype, so a Bb parent and a BB parent get the same answer.
• Single-outcome Punnett tools (Calculator.city eye genetics pages): a clean BB/Bb/bb square that returns only brown or blue. Correct classroom maths, but no green or hazel outcomes and no colour-mode table for parents who do not know their genotypes.
• Elaborate allele-chain tools (punnettsquare.org): a six-allele dominance chain with downloadable squares. Richer than this page's model, and worth knowing about, but harder for a first-time reader to audit, and still a simplification presented without a full published table.
• The gap this page fills: both routes on one page, the exact model stated in plain language including its weakest points (the flat hazel rows, the missing hazel in genotype mode, the single-genotype ignore rule), the Punnett square drawn for your cross, and the complete colour table published so any result can be checked without running the tool.

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