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The inbreeding coefficient, or COI, measures how genetically related a planned pairing is. It tells you the probability that any given gene locus in the offspring will be identical by descent from a common ancestor. The higher the COI, the more likely the offspring are to inherit two copies of the same recessive allele, which increases the risk of expressing recessive health conditions.
Most breeders learn about COI in the context of health testing. OFA, AKC, and breed health organizations recommend keeping COI below certain thresholds for each breed. Calculating it by hand requires tracing paths through every common ancestor in the pedigree. This tool does that calculation automatically from a 3-generation pedigree.
Enter the names of ancestors on both sides. The tool identifies any name that appears on both the sire and dam side and calculates its contribution to the COI. Use consistent names: if the same dog appears in multiple positions, spell the name exactly the same way each time.
Sire side Dam side
The COI is expressed as a percentage. A result of 0% means no common ancestors were detected in the 3 generations you entered, not that the planned offspring will have zero inbreeding. A COI of 6.25% is the equivalent of a half-sibling mating or a grandparent-grandchild mating. A COI of 12.5% is equivalent to a full-sibling mating.
Most breed health organizations recommend keeping COI below 6.25% for any single pairing and tracking population-level average COI over time. In breeds with small effective population sizes, every breeding decision affects the long-term genetic health of the breed.
A 3-generation pedigree can miss significant inbreeding. If both the sire and dam trace to the same popular sire from 4 or 5 generations back, this tool will not detect it. A 5-generation COI calculation requires 62 ancestor slots. A 10-generation calculation requires hundreds. The deeper the pedigree, the more accurate the result.
For breeds with extensive registry data, platforms like Breed Ledger calculate COI from a full pedigree database rather than from manually entered names. That gives you a more accurate number without having to look up and enter ancestors by hand. The records and genetics app built by BBD includes the same deep pedigree COI analysis for programs that want it integrated with their animal records.
COI is one input into a breeding decision, not the only one. A pairing with a moderate COI might be the right choice to preserve a rare trait or type. A pairing with a low COI might still produce health problems if both parents carry the same recessive allele. COI is a probability estimate, not a guarantee.
Breeders who actively manage COI typically use it to set a ceiling on any single pairing, track the average COI in their program over time, and deliberately seek out unrelated lines when the program average starts to climb. This is called genetic diversity management, and it is one of the things that separates a breeding program from a breeding operation.
The breed club software built through BBD tracks COI at the breed level, flagging pairings that would push the population average above threshold. And if you are tracking your own waitlist alongside these breeding decisions, the puppy waitlist guide covers how to manage that side of the program.
Reptile breeders can pair this COI check with the free crested gecko morph calculator to predict both genetic diversity and trait outcomes — Lilly White, Axanthic, Phantom, and more — for the same planned pairing.
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