The coefficient of inbreeding (COI) is a single percentage that tells you how closely related a cat’s parents are — and therefore how much genetic duplication a kitten is likely to carry. It’s one of the most useful numbers a breeder can look at.
Why it matters
Higher inbreeding concentrates genes — both good and bad. A lower COI generally means more genetic diversity, which is associated with better health, fertility and resilience. It’s a guide, not an absolute rule, but it’s an important one.
How it’s calculated
The classic method is Wright’s coefficient, which traces common ancestors through the pedigree. The more generations you include, the more accurate the figure — which is why a deep, correct pedigree matters.
What counts as a good COI?
There’s no single magic number, and norms vary by breed and population. As a rule of thumb, lower is safer; many breeders aim to keep matings well below the level of a half-sibling pairing. Compare against your breed’s typical range.
Use it before you mate, not after
The real value is in trial matings: check the predicted COI of a pairing before you commit. Perfect Pedigrees calculates COI for any cat or trial mating instantly, in plain English.
