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 to 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