COI calculator
Work out Wright's coefficient of inbreeding for a planned mating. It works for cattle, sheep, goats, horses, dogs or any animal with a pedigree, and needs no account.
The pedigree
Type each name the same way wherever it appears. A name on both sides is a common ancestor.
Result
Enter the sire and dam, and as many grandparents as you know, then press Calculate COI.
What the ranges mean
- < 3.125%
- Excellent
- 3.125 – 6.25%
- Good
- 6.25 – 12.5%
- Moderate
- 12.5 – 25%
- High
- ≥ 25%
- Very High
Keep your own records
A free account saves pedigrees and health records, and works out COI from the animals you've stored.
Create a free accountFree: 5 animals and 2-generation pedigrees.
How to use this COI calculator
Enter the names of the sire (father) and dam (mother) in the first row. Then fill in their parents (the grandparents) in the second row. If you know the great-grandparents, expand the third generation for a more accurate calculation.
The calculator detects common ancestors automatically. If the same animal appears on both the sire's and dam's side of the pedigree, they are inbred. The COI percentage tells you how much genetic overlap to expect in the offspring.
This tool uses Wright's formula for calculating the Coefficient of Inbreeding, the same method used by professional breed registries worldwide. It works for dogs, cattle, goats, horses, sheep, and any other species with pedigree records.
Why COI matters for breeding
The Coefficient of Inbreeding represents the probability that two alleles at any given locus are identical by descent. Inbreeding increases the chance of offspring inheriting harmful recessive genes from both parents.
Higher COI values are associated with reduced immune function, lower fertility, shorter lifespan, and higher rates of genetic disease — often called inbreeding depression. Most breed registries recommend keeping COI below 6.25% (the equivalent of mating half-cousins); values above 12.5% significantly increase health risks.
Calculating COI before breeding helps you make informed decisions about which pairings will produce the healthiest offspring while maintaining breed type and genetic diversity.