Olive egger calculator
Pick two parent breeds to see the egg color you can expect from the first cross (F1) and from breeding it darker (F2) — with visual swatches.
F1 (first cross)
~100% of chicks carry the blue-egg gene
F2 (breed an F1 hen back to the darker-egg parent)
Back-crossing to a darker-brown bird is how breeders deepen olive across generations.
These are expected tendencies, not guarantees — eggshell brown is polygenic, so individual hens vary. See the egg-color genetics guide for how blue and brown combine.
How olive eggs happen
There are really only two base shell colors: white and blue. The **blue-egg gene** (oocyan) is dominant and deposits blue pigment through the whole shell. **Brown** is a separate surface coating laid over the base, and it's polygenic — controlled by many genes, so it stacks additively. When a blue base gets a brown coating, the result reads as green or, with a heavy coating, olive.
That's why the classic olive egger is a blue-egg breed crossed with a very dark-brown breed: the F1 carries one blue gene plus about half the dark parent's brown, giving a medium olive. Breed that F1 back to a dark-brown bird and the brown genes concentrate, pushing the F2 toward a deeper olive. This calculator models those tendencies — see the full guide for the details.
Frequently asked questions
- How does the olive egger calculator work?
- It combines the two things that make egg color: the blue-egg gene (dominant — a bird carrying it lays a blue-base shell) and the brown coating (polygenic — deeper on breeds like Marans). Blue base + brown coating = olive; the more brown, the deeper the olive.
- What crosses make the best olive eggers?
- A pure blue-egg breed × a very dark-brown breed — e.g. Ameraucana or Cream Legbar over Black Copper Marans or Penedesenca. All F1 hens then carry one blue gene plus about half the dark parent's brown.
- How do I get a darker olive egg?
- Breed an F1 olive egger hen back to a dark-brown-egg rooster (a backcross). About half the F2 hens still carry the blue gene, and the brown genes concentrate, so those eggs come out a deeper olive.
- Is the predicted color guaranteed?
- No — brown coating is polygenic, so individual hens vary and color also fades over a laying cycle. Treat the swatches as expected tendencies, not a promise.