Coefficient of Inbreeding (COI) Calculator
Last reviewed: July 3, 2026. Built and reviewed by the BreederHQ Operations Team, working with active breeders across nine species.
Estimate Wright’s coefficient of inbreeding from a pedigree. Free, no signup, runs in your browser.
Enter the planned sire and dam, then fill in as many ancestors as you know up to five generations. The tool finds common ancestors automatically and shows each one’s contribution. For automatic COI on every planned breeding from your full pedigree library, use it inside BreederHQ.
Estimated Coefficient of Inbreeding
Common ancestors found
No common ancestors detected in the pedigree you entered. COI is 0% at this pedigree depth. If you know there is shared ancestry further back, your registry’s deep-pedigree COI may read higher.
Hand-entering 30 ancestors per mating gets old fast. In BreederHQ, every planned breeding gets a live COI from your full pedigree library — dogs, cats, horses, goats, sheep, rabbits, alpacas, llamas, and cattle — with no manual entry. The number sits next to health testing, contracts, deposits, and waitlists for the same planned mating.
What COI Tells You (and What It Doesn’t)
COI estimates the probability that the two alleles at any random locus in the planned offspring are identical by descent — inherited from the same ancestor on both sides. It is a population-genetics shorthand for "how related are these two animals through their pedigree."
What COI does tell you. Whether a planned mating is going to compound shared ancestry that already exists in the line. Whether two candidate matings would differ in their genetic-diversity cost. Whether the line-breeding you are planning is mild, moderate, or close.
What COI does not tell you. Whether either animal carries a specific disease allele — that is what genetic testing is for. Whether the offspring will inherit a particular trait. Whether the breed average for COI is reasonable in absolute terms (some closed registries have arithmetically high baselines). Whether a low COI from a five-generation calculation is actually low when computed against a deep pedigree.
Reference points. A parent-to-offspring mating produces a COI of 25%. A full-sibling mating also produces 25%. A first-cousin mating produces 6.25%. An unrelated mating with no shared ancestors in the pedigree produces 0%. Most breed clubs publish a breed-average COI that gives you a baseline to compare against; check your registry or breed club for the breed-specific number.
How to Read the Result
- 1 Look at the common ancestors first. The list under the headline number shows every ancestor that appears on both sides of the pedigree you entered, with its generation depth and its contribution to the total. If the list is empty, the COI is 0% at this depth.
- 2 Compare two matings at the same depth. The most useful thing this tool does is let you compare two planned matings of the same animal against different mates. Run both, see which produces lower COI, and you have a real input into the decision.
- 3 Cross-check against your registry’s number. A five-generation hand-entered COI will usually read lower than a deep-pedigree registry COI on the same animal. Use the registry’s number for absolute reporting and this tool for quick what-if comparisons.
- 4 Decide alongside everything else. COI is one variable. Health testing, temperament, working ability, breed standard, and your buyer pipeline all matter too. A low COI on a mating that ignores everything else is not a good breeding.
Stop Calculating One Breeding at a Time
A free hand-entered calculator is fine for a one-off question. It is a slog for an active breeding program with a deep pedigree library, multiple planned matings, and a waitlist that needs to know which litters are actually going to happen.
Inside BreederHQ, every animal in your pedigree library carries its own subtree forward. When you plan a breeding, COI is calculated against the full depth of pedigree you have on record — not just the five generations you can fit on screen — and it updates in real time as you add new ancestors. The number sits on the breeding plan alongside health testing, contracts, deposits, and waitlist matches for that planned mating. Across nine species: dogs, cats, horses, goats, sheep, rabbits, alpacas, llamas, and cattle.
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Frequently Asked Questions
What is the coefficient of inbreeding (COI)?
COI is the probability that the two alleles an animal carries at any random locus are identical by descent — that is, both came from the same ancestor. A COI of 0% means no detectable shared ancestry in the pedigree you supplied. A COI of 25% is the result of a parent-to-offspring or full-sibling mating. COI is a pedigree statistic, not a genetic test, and it only sees as far back as the pedigree you give it.
How does this calculator work?
It uses Wright’s path method. For each ancestor that appears on both the sire side and the dam side, it adds (1/2)^(n1 + n2 + 1) × (1 + F of that ancestor), where n1 and n2 are the number of generations from the sire and dam back to the common ancestor. The result is the planned offspring’s estimated COI. Up to five generations are supported. If you do not supply an ancestor’s own inbreeding (F) value, it is treated as zero, which is the standard assumption when ancestor F is unknown.
How many generations of pedigree should I enter?
Five generations is the depth most breed clubs and pedigree databases use for reported COI, and it is the depth this calculator supports. Three generations will catch obvious doubling on grandparents and great-grandparents. Five generations will catch line-breeding that hides deeper in the pedigree. Anything beyond five generations adds diminishing weight per ancestor (each additional generation halves the contribution) and is rarely worth manual entry. Inside BreederHQ, planned-breeding COI is calculated from your full pedigree library, not just the five generations you can fit on screen.
What is a high COI?
There is no single answer because the right threshold varies by species, breed, and population. Many working dog breed clubs treat a COI above the breed average as a yellow flag and above twice the breed average as a red flag. Livestock breeds tolerate different ranges depending on selection history. The single useful rule across species: a single planned mating that lifts COI well above your breed’s baseline gives away genetic diversity that the next generation cannot get back. Treat this number as one input into a breeding decision, alongside health testing, temperament, and population-level breed advice.
Does the calculator save anything?
No. Everything runs in your browser. Nothing is sent to a server, nothing is logged, no signup is required. Refreshing the page clears the form. If you want COI to live on every planned breeding alongside health testing, contracts, and waitlists, that is what BreederHQ does in-app.
How is this different from the COI in BreederHQ?
This public calculator asks you to enter up to 30 ancestors by hand and computes COI from what you typed. The in-app COI runs against your full pedigree library, automatically — every breeding you plan gets a live COI based on every dog, cat, horse, goat, sheep, rabbit, alpaca, llama, or cattle pedigree you have on record, with no manual entry. It also sits alongside COI history for previous matings, breed-specific reference ranges where we have them, and the health-testing and temperament data tied to each animal.
Will this give me the same answer as my breed registry’s COI?
Not necessarily. Registry COI numbers are usually computed against the full registered pedigree going back many generations — sometimes to a breed’s founding population. A five-generation hand-entered calculation only sees five generations, so it will typically read lower than a deep registry calculation on the same animal. Use this tool to compare two planned matings on the same depth of pedigree; use your registry’s number for absolute baseline reporting.
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