Chicken Inbreeding (COI) Calculator
Wondering how inbred the chicks of a pairing would be? Pick how the two birds are related and this calculates the offspring's coefficient of inbreeding (COI) — the chance their two gene copies are identical because the parents share ancestors.
Quick reference
| Relationship of parents | Offspring COI |
|---|---|
| Unrelated (outcross) | 0% |
| First cousins | 6.25% |
| Half siblings | 12.5% |
| Grandparent × grandchild | 12.5% |
| Aunt/uncle × niece/nephew | 12.5% |
| Parent × offspring | 25% |
| Full siblings | 25% |
Rough guide: under ~6.25% is low (a cousin cross or less), 6.25–12.5% is moderate line-breeding, and above that the risks to vigor, fertility, and hatch rate climb. Some line-breeding is normal — the key is doing it on purpose and knowing when to outcross.
Want this for your actual flock?
Record each bird's sire & dam and ChickenAncestry computes every bird's COI — plus a test-mating tool that previews a real pairing before you set eggs.
Track your flock free
Record each bird's sire & dam and ChickenAncestry computes every bird's COI — plus a test-mating tool that previews a real pairing before you set eggs.
Track your flock free