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Ball python morph calculator — 55 genes, real inheritance.
Pick a sire and a dam and see the odds for every possible hatchling — including the hets carried invisibly and the poss-het figure you would advertise them as. Recessive, incomplete dominant and dominant genes are modelled the way they actually pass on. Six allelic complexes are modelled as single loci rather than multiplied together, so a Blue Eyed Leucistic parent gives the right answer. Anything this calculator cannot model honestly, it names.
♂ Sire
♀ Dam
What the hatchlings can look like
Carried invisibly (hets)
The first figure is the chance across the whole clutch. Poss het is the figure that goes on a price list — the odds for a hatchling that does not show the trait, which is why het × het advertises at 66% rather than 50%.
How ball python genetics work
Three modes of inheritance, 55 genes
Every gene in this calculator is stored with how it actually passes on — not a lookup table of published pairings, so it works on combinations nobody has charted.
Recessive
Two copies to show. One copy is an invisible carrier — a het — which is how a normal-looking animal throws Piebalds.
Albino · Axanthic · Candy · Caramel · Clown · Desert Ghost · Genetic Stripe · Ghost · Lavender Albino · Monsoon · Piebald · Red Axanthic · Scaleless · Sunset · Toffee · Tri-Stripe · Ultramel
Incomplete dominant
One copy shows. Two copies give the super form — Super Pastel, Ivory, or a Blue Eyed Leucistic, depending on the gene. Spider and Woma sit here rather than under dominant: they do have a super form, it is just that Super Spider does not survive.
Asphalt · Bamboo · Banana · Black Pastel · Butter · Calico · Champagne · Chocolate · Cinnamon · Coral Glow · Desert · Enchi · Fire · GHI · Gravel · Hidden Gene Woma · Lesser · Mojave · Mystic · Orange Dream · Pastel · Phantom · Red Stripe · Russo · Special · Spider · Spotnose · Sulfur · Vanilla · Woma · Yellowbelly
Dominant
One copy or two, the animal looks the same. No distinct super form to breed toward.
Dorsal · Granite · Leopard · Pinstripe
Where most calculators go wrong
Six allelic complexes, modelled as one locus each
Some genes are not separate genes at all — they are different versions of the same one, and an animal can carry at most two of them. Multiply them together and you get impossible answers: a Blue Eyed Leucistic bred to a normal reported as throwing 25% normals, when it cannot throw a normal at all. Each group below is modelled as a single locus with several alleles.
Blue Eyed Leucistic
Bamboo · Butter · Lesser · Mojave · Mystic · Phantom · Russo · Special
Spider
Champagne · Chocolate · Hidden Gene Woma · Spider · Spotnose · Woma
Super Stripe
Asphalt · Gravel · Yellowbelly
Black Eyed Leucistic
Fire · Sulfur · Vanilla
Albino
Albino · Candy · Toffee
8 Ball
Black Pastel · Cinnamon
Complex membership is still being settled by breeding trials, so only groupings carried by more than one published source are encoded here. Enchi is the deliberate omission — MorphMarket’s community list places it in the 8 Ball complex and the Ball Street Journal’s does not, and guessing wrong on a gene this common would change answers people price animals on. It stays an independent locus until the hobby agrees.
Named combinations
“Bumblebee” is not a gene
The hobby names combinations as if they were single traits. They are two or more genes at once — enter the genes and the calculator produces the combination.
| The name | What it actually is |
|---|---|
| Bumblebee | Pastel + Spider |
| Killer Bee | Super Pastel + Spider |
| Queenbee | Pastel + Spider + Enchi |
| Lemon Blast | Pastel + Pinstripe |
| Blue Eyed Leucistic (BEL) | Any two of: Mojave, Lesser, Butter, Phantom, Mystic, Bamboo, Russo, Special |
| Ivory | Two copies of Yellowbelly |
| Highway | Yellowbelly + Gravel |
| Moonglow | Albino + Axanthic + Lavender Albino |
Questions
Asked before every pairing
What does 66% het mean?
A normal-looking hatchling from two het parents has a 2-in-3 chance of carrying the recessive gene — the visual outcome has been ruled out, which shifts the odds. This calculator accepts 100%, 66% and 50% het parents and carries the probability through the maths rather than treating “het” as certain.
How are allelic complexes handled?
Mojave, Lesser, Butter, Phantom, Mystic, Bamboo, Russo and Special are alleles of one locus — the BEL complex — so an animal carries at most two of them, never both as separate genes. This calculator models a complex as a single locus with several alleles rather than multiplying the genes together, which is what lets it get a Blue Eyed Leucistic parent right: a BEL is Mojave over Lesser and holds no normal copy at all, so bred to a normal it throws half Mojaves and half Lessers — never a normal, and never another BEL. Calculators that treat the two as separate genes report 25% normals from a pairing that cannot produce one. Five other groups work the same way: the Spider, Super Stripe, Black Eyed Leucistic, Albino and 8 Ball complexes.
What is a poss het, and why 66%?
Two figures answer two different questions. Half of a het × het clutch carries the gene — that is the chance across every egg. But a quarter of the clutch shows the trait, and once you can see which ones those are, the normal-looking hatchlings are two in three. 66% poss het is the figure that goes on a price list, and this calculator prints both.
Why the caution on Banana and Coral Glow?
They are sex-linked: the male-to-female ratio of banana hatchlings depends on which parent carries the gene. This calculator does not pretend to model that — it flags it, because a confident wrong number is worse than an honest limitation.
What happens with Spider, and why is it not 75/25?
Spider and Champagne are alleles of one locus, and three of that locus’s combinations do not produce a living hatchling: Super Spider, Super Champagne, and Champagne over Spider. Those are removed from the clutch and the rest renormalised, so Spider × Spider reads 67% Spider and 33% normal rather than the 75/25 you get by counting eggs that never hatch. The page tells you how much of the clutch was removed. Spider also carries a neurological wobble, which is flagged separately.
Is this calculator really free?
Yes — no account, nothing uploaded, everything runs in your browser. It is the same engine that powers SKS Exotics, the ball python collection and breeding tracker, where the calculator works directly on the animals you keep.
Now imagine it already knows your animals.
In SKS Exotics this same calculator runs on your actual collection — pick two of your snakes and the odds appear, then the pairing is tracked from first lock to hatch. Free for 5 animals.