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Free horse color calculator & foal color genetics predictor. Calculate potential foal coat colors based on parent genetics using Extension and Agouti genes. Our calculator uses Mendelian inheritance to predict bay, black, and chestnut probabilities for your breeding program with detailed genetic explanations and probability breakdowns.
Last updated: February 2, 2026
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E = black pigment, e = red pigment
A = bay pattern, a = no restriction (black)
E = black pigment, e = red pigment
A = bay pattern, a = no restriction (black)
Based on parent genetics, this cross can produce 3 different base colors with varying probabilities.
Genotype: Ee Aa
Brown/reddish body with black points (mane, tail, lower legs). Most common color.
Genotype: ee Aa
Reddish-brown throughout, no black points. Also called sorrel in some breeds.
Genotype: Ee aa
Pure black throughout, may fade to brown in sun. Less common than bay.
Genetics Explained:
Extension Gene: Extension gene (E/e) controls whether a horse produces black or red pigment. E is dominant (black), e is recessive (red/chestnut).
Agouti Gene: Agouti gene (A/a) restricts black pigment to points (mane, tail, legs). Only visible on black-based horses (E_). A is dominant, a is recessive.
Base Colors: The three base colors are Bay (E_ A_), Black (E_ aa), and Chestnut (ee __). All other colors are modifications of these.
Breeding Notes:
Important Note:
This calculator predicts base coat colors only (Bay, Black, Chestnut). Additional genes for dilutions (Cream, Dun, Champagne), patterns (Tobiano, Appaloosa), and white markings are not included. For precise breeding predictions, consider genetic testing through UC Davis or Animal Genetics.
Genotype
E_ A_
Brown body with black points (mane, tail, legs)
Genotype
E_ aa
Pure black throughout, no brown shading
Genotype
ee __
Reddish-brown throughout, no black pigment
Function
Pigment Type
E = black pigment, e = red pigment (recessive)
Function
Pattern Control
A = bay pattern, a = allows solid black
Pattern
Dominant/Recessive
Each parent passes one copy of each gene
For Ee Aa (bay) × Ee Aa (bay) breeding:
Bay
56%
Chestnut
25%
Black
19%
Our horse color calculator uses Mendelian genetics to predict foal coat colors based on parent genotypes for the Extension and Agouti genes. These two genes determine the three base horse colors: bay, black, and chestnut. The calculator creates a Punnett square combining all possible allele combinations from each parent to determine color probabilities.
Extension Gene (E/e):
E = dominant, produces black pigmente = recessive, produces red pigmentEE or Ee = black-based colorsee = chestnut (always)Agouti Gene (A/a):
A = dominant, restricts black to points (bay)a = recessive, allows solid blackOnly affects black-based horses (E_)E_ A_ = BayE_ aa = Blackee __ = Chestnut (agouti irrelevant)Each parent contributes one allele per gene. The calculator evaluates all 16 possible combinations (4 Extension × 4 Agouti) to determine color probabilities.
Horse coat color follows standard Mendelian inheritance with dominant and recessive alleles. The Extension gene is epistatic to Agouti, meaning it can mask Agouti's effects. Chestnuts (ee) cannot express Agouti because there's no black pigment to restrict. This is why chestnuts can be AA, Aa, or aa without visible difference, but they can pass Agouti alleles to offspring.
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Get Custom Calculator for Your PlatformResult: Bay most likely at 56%, but chestnuts and blacks possible
This cross demonstrates how heterozygous bay parents can produce all three base colors
ee × ee breeding
Result: 100% Chestnut foals
EE aa × ee breeding
Result: 100% Bay foals (Ee Aa)
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