Foal Coat Color Probability Calculator
Select the known genotypes for sire and dam. The calculator estimates foal phenotype probabilities using four major loci: Extension, Agouti, Cream, and Grey.
Sire (Stallion)
Dam (Mare)
Educational model only. Real-world color outcomes may differ due to additional genes (dun, roan, champagne, silver, pearl, sooty, flaxen, white patterning, and modifiers not modeled here).
How this horse color breeding calculator works
This tool combines basic Mendelian inheritance across four common color loci to estimate the probability of each foal coat color. You choose each parent's genotype, and the script computes all possible allele combinations a foal could receive.
Genes included in the model
- Extension (E/e): controls black pigment production. e/e creates red-based coats.
- Agouti (A/a): restricts black pigment to points when black pigment is present.
- Cream (N/Cr): dilution gene that lightens coat color (single and double dilution).
- Grey (G/g): dominant progressive depigmentation overlay; greys are born a base color and lighten with age.
Color outcomes this calculator predicts
Based on the selected genotypes, outcomes include chestnut, bay, black, palomino, buckskin, smoky black, cremello, perlino, smoky cream, and their grey-overlay versions.
Base color logic
- e/e = red base (chestnut family)
- E/_ + A/_ = bay family
- E/_ + a/a = black family
Cream dilution logic
- 0 Cream alleles: chestnut / bay / black
- 1 Cream allele: palomino / buckskin / smoky black
- 2 Cream alleles: cremello / perlino / smoky cream
Why results are probabilities, not guarantees
Each breeding passes one allele per locus from each parent. Even with known parental genotypes, each foal is still a random draw from all valid combinations. Over many foals, real outcomes should approach the calculator's percentages.
Practical breeding note
If your program depends on a specific color outcome, DNA test both sire and dam before planning matings. The calculator is most useful when entered with confirmed genotypes rather than visual guesses.
Frequently asked questions
Does this include white markings or pinto patterns?
No. White spotting and pattern loci are not included in this model.
Does grey hide base color?
Yes. Grey can eventually obscure base coat appearance, but genetically the horse still has an underlying base color, shown here as “Grey (born X).”
Can two non-grey parents produce a grey foal?
Not in standard inheritance for the Grey locus. At least one parent must contribute a G allele.