Trace every ancestor
The tool walks both pedigrees out to the depth you picked, usually four generations. That's 30 ancestor slots in total for a 4-gen calculation.
Free tool · 01 · COI Calculator
How inbred
is this pairing?
Run the Coefficient of Inbreeding math on a proposed pairing before you commit to a season. Pick a sire and dam, choose how many generations back you want to look, and the tool returns a percentage, a verbal interpretation, and the common ancestors driving the score.
Free · no signup~5 minutesAll species
Pedigree input
Sire lineDam line
Parents
Grandparents
Great-grandparents
Fill in the pedigree above and press Calculate. The result lands right here.
How it works
Three steps, no
mystery math.
COI calculation is a known formula. The tool just runs it for you and shows the work. Here's what's happening behind the scenes when you press Calculate.
Find the shared ones
Any animal that appears in both the sire's and the dam's pedigree gets flagged. Those are the contributors to the COI score.
Sum the contributions
Each shared ancestor adds a percentage based on how recently they appear. Closer ancestors weight heavier. Add them up, that's the COI.
Once you've got the number
You picked a pairing.
Now put it in writing.
COI gives you the math. The Breeder Contract Kit covers what to do with it: the breeding rights contract that defines what each side gets, the deposit agreement that holds buyers to the litter you just planned, and the co-ownership template if you're sharing the dam with a co-breeder.
Common questions
A few things people
ask about COI.
For the depth you analyze, yes — it's Wright's formula, which is the standard everywhere. Registry COIs typically use much deeper pedigrees (8+ generations) and reach back further than most breeders have on paper. The number you get here is a point-estimate from what you typed in, not a substitute for an official registry calculation.
Empty slots are treated as unknown — they can't share lineage with anything else, so they contribute zero. If half a pedigree is blank, the resulting COI is a lower bound, not the truth.
By name, normalized (case-insensitive, trimmed). "NARCO VII" and "Narco VII " match. "Narco 7" and "Narco VII" do not — pick one spelling and use it consistently across both sides of the pedigree.
Low (under 6.25%) is fully outcrossed in working-program terms. Moderate (6.25 to 12.5%) is line-bred but workable. Elevated (12.5 to 18.75%) concentrates traits more aggressively. High (above 18.75%) is heavy line-breeding or inbreeding — sometimes deliberate, always worth being explicit about.
Drop your email in the box under the result and you'll get a copy in your inbox. Your address goes on the Field Notes list (one short letter every other week, one-click unsubscribe).
Not in this free tool. On Breed Ledger the COI calculator imports pedigrees from a PDF, an image of a registration paper, or a URL from supported pedigree databases.
Want this on every pairing you plan?
Breed Ledger runs the COI math automatically every time you set up a pairing, plus pedigree generation, health-test calendars, and buyer-facing animal pages. Free tier covers most working programs.
See Breed Ledger