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Free horse color calculator and foal color predictor for the three base coats: bay, black, and chestnut. Enter sire and dam Extension (E/e) and Agouti (A/a) genotypes to see Mendelian probabilities — ideal for breeding planning when you have test results or educated genotype guesses.
Last updated: May 25, 2026
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This cross yields 3 base colors across 16 Punnett combinations.
Sire Ee Aa (Bay) × Dam Ee Aa (Bay)
9 of 16 combinations · example genotype EE AA
Brown/reddish body with black points (mane, tail, lower legs). Most common base in many breeds.
4 of 16 combinations · example genotype ee AA
Red/chestnut/sorrel with no black points; also called sorrel in some stock breeds.
3 of 16 combinations · example genotype EE aa
Solid black coat on E_ aa horses; may sun-fade to brown in summer.
Genetics recap
Extension (E/e): E is dominant; at least one E → black pigment possible. ee → chestnut regardless of Agouti.
Agouti (A/a): only visible on E_ horses. A restricts black to points (bay); aa allows solid black body.
Default: heterozygous bay × heterozygous bay (Ee Aa × Ee Aa) — the classic teaching cross.
56%
9 of 16 combinations · e.g. EE AA
25%
4 of 16 · both parents must pass e
19%
3 of 16 · needs a from both parents
Bay × Bay (Ee Aa × Ee Aa)
Bay 56% · Chestnut 25% · Black 19%
Chestnut × Chestnut (ee × ee)
Chestnut 100%
Black × Black (EE aa × EE aa)
Black 100%
Bay × Chestnut (EE AA × ee aa)
Bay 100%
Black × Bay (EE aa × Ee Aa)
Bay 50% · Black 50%
Brown/reddish body with black points (mane, tail, lower legs)
Solid black pigment when Agouti does not restrict black to points
Red/chestnut/sorrel base; Agouti has no visible effect without black pigment
A bay coat does not prove EE or AA — many bays are Ee Aa and can produce chestnut or black foals.
| Visible coat | Common genotypes | Breeding note |
|---|---|---|
| Bay | Ee Aa, EE AA, EE Aa, Ee AA | Many bays are Ee Aa — can throw chestnut or black foals |
| Black | EE aa, Ee aa | Ee aa black horses can produce bay foals if mate carries A |
| Chestnut | ee AA, ee Aa, ee aa | All chestnuts are ee; Agouti genotype is hidden but still inherited |
| Gene | Typical effect |
|---|---|
| Cream (CR) | Dilutes red → palomino; black+bay → buckskin; double cream → cremello/perlino |
| Dun (D) | Primitive markings, lighter body; buckskin dun on bay base |
| Gray (G) | Progressive white hair; born colored, grays over time |
| Champagne (CH) | Dilutes pigment; gold champagne on chestnut base |
| Silver (Z) | Dilutes black pigment; flaxen mane on black-based |
| Tobiano / Overo / Sabino | White spotting patterns — separate from base color |
| Leopard Complex (LP) | Appaloosa spotting — independent inheritance |
| Frame Overo (O) | Pattern + lethal white risk when homozygous — test before breeding |
Horse base coat color follows Mendelian inheritance at two loci. Extension (E/e) switches black pigment on or off at the base level. Agouti (A/a) patterns black on E_ horses into bay vs solid black. The calculator enumerates every allele combination from both parents — 4 Extension outcomes × 4 Agouti outcomes = 16 equally likely foal genotypes.
ee __ → Chestnut
E_ A_ → Bay (AA or Aa)
E_ aa → Black
Agouti is epistatic to Extension only in the sense that ee masks Agouti visually — but Agouti alleles still segregate in chestnut lines.
Most likely: Bay at 56% — but 25% chestnut and 19% black are real outcomes.
Contrast: Chestnut × Chestnut → Chestnut 100%; Bay (EE AA) × Chestnut → Bay 100%.
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