How inbred
is this pairing?

For the depth you analyze, yes. It is 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, so a deeper calculation usually comes back higher. If you are comparing against the Kennel Club's Mate Select or an AKC pedigree, expect small differences from generation depth and how complete each registry's records are. 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). "DUKE VII" and "Duke VII " match. "Duke 7" and "Duke VII" do not, so 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% up to 12.5%) is line-bred but workable. Elevated (12.5% up to 18.75%) concentrates traits more aggressively. High (18.75% and above) is heavy line-breeding or inbreeding, sometimes deliberate, always worth being explicit about. Each threshold is the floor of the bucket it names, so exactly 18.75% reads as High.

Drop your email in the box under the result and you'll get a copy in your inbox. Calculating without entering an email keeps everything in your browser, so nothing leaves your machine. If you do enter one, your address goes on the Field Notes list (one short letter every other week, one-click unsubscribe).

Yes. Press "Copy a link to this result" and send the link. It reopens the tool with the same pedigree and the same score already calculated. The pedigree is encoded in the part of the link after the # symbol, which browsers never transmit to a server, so the names travel only between you and the person you send the link to.

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.

The slots start pre-filled with sample data from an example French Bulldog program so you can see what a real calculation looks like, and the preset buttons load known relationships like full siblings or first cousins. In real use, you type in your own animals' pedigrees from your registration papers, your records app, or your registry export. Nothing is stored unless you ask to save the result.

For most working programs, under 6.25 percent is low and safely outcrossed, and under about 10 percent is a common target for a healthy pairing. Line-bred programs often run higher on purpose. What matters more than any single number is the trend across your program and whether the concentration is deliberate. The calculator shows where a proposed pairing lands so you can decide before you commit. The Kennel Club publishes a breed average COI for many breeds, and the AKC and its parent clubs publish diversity guidance, so find your breed's benchmark and aim at or below it.

There is no universal cutoff, but above about 18.75 percent, roughly a half-sibling or grandparent-to-grandchild pairing, is heavy inbreeding worth being explicit about. Many breeders treat 12.5 percent, the equivalent of a first-cousin cross, as the point to slow down and justify the pairing. Higher COI concentrates the traits you want and the ones you do not, which raises the chance of surfacing recessive problems and lowers genetic diversity.

No. Some inbreeding is how breeds got distinct in the first place. The goal is intentional, tracked, and balanced across generations. A 12% COI on a single pairing isn't a disaster. 12% on every pairing across five generations is how you produce a bottleneck. The tool is here to make the trend visible so the next pairing can compensate.

It uses Wright's formula. For every ancestor that appears on both the sire's and the dam's side, you add a contribution based on how many generations back each path runs, so closer shared ancestors count for much more than distant ones. Sum every shared-ancestor path and you have the coefficient. This tool traces both pedigrees, finds the shared ancestors, and shows each contribution so you can see the math rather than just the result.

More generations give a more accurate number, because inbreeding hidden deeper in a pedigree only appears when you look back far enough. Three or four generations catch obvious recent doubling, while registry calculations often use eight or more. This tool runs 3 to 6 generations. Use the deepest pedigree you have reliable names for, and treat a shallow calculation as a lower bound rather than the whole picture.

Yes. COI math is species-agnostic. The breed-specific "what's normal" thresholds change, but the formula doesn't. I use this tool on my own gecko program with the same engine. Species-specific improvements, like reptile het calculations and the line-breeding patterns common in cattle, are in the queue.