Skip to content
Sign inBook a demo

COI calculator

Work out the COI of a pairing.

Enter the sire, the dam and their ancestors. See the COI of their offspring, the loops through each shared ancestor (the 100 largest when there are more), and Wright’s formula written out with your own numbers.

Instrument No. 001 · Inbreeding analysis · Your pedigree

Type a pedigree, read the loops.

Load a known relationship

Result

Enter the sire and the dam to see the COI of their offspring.

Sire and dam
Grandparents
Great-grandparents

0 of 14 ancestors entered

The pedigree is written into the link after the #, so anyone you send it to can read it. Browsers do not send that part to a server.

Method: Wright’s path formula over the ancestors you enter. A blank name is an unknown ancestor.Work out an outcross program

One loop per route

Each route from the sire up to a shared ancestor and back down to the dam is one loop. Its share is one half raised to the power of (the steps on both sides plus one).

Inbred ancestors count more

When a shared ancestor is itself inbred, its loop is multiplied by one plus that ancestor’s own coefficient.

Matching names are one animal

Names that match, ignoring capital letters and extra spaces, are read as the same animal. Spell each animal the same way wherever it appears.

How it works

Three steps, all shown.

Enter the pedigree

Type the sire and the dam, then their parents and further back. Choose 3 to 7 generations, paste one name per line, or load a known relationship.

Find the shared ancestors

An animal on both the sire’s side and the dam’s side is a common ancestor. Every separate route to it is a loop.

Add up the loops

The COI of the offspring is the sum of every loop’s share. The formula under the result shows each term, up to 12, and counts the rest.

Questions

Questions about COI calculators.

What does the COI of a pairing measure?
It is the chance that the two copies of a gene in an offspring came from the same ancestor, worked out from the pedigree you enter. It describes the recorded pedigree. It reads no DNA results.
Is this the same arithmetic Breed Ledger uses for pairings?
Yes. This page runs the same calculation as the pairing analysis in Breed Ledger, which counts up to 11 generations of ancestors. A registry’s figure can differ if it counts a different number of generations or holds different records, so compare two figures only when both used the same depth and the same records.
Why does a blank name matter?
A blank slot is an unknown ancestor, and an unknown ancestor cannot share a loop. A fuller pedigree can raise the COI but never lower it, so a short pedigree can understate it.
How many generations should I enter?
As many as you have reliable names for. The grid holds 3 to 7 generations, counting the offspring as the first, which is 6 to 126 names.
Is my pedigree saved or sent anywhere?
No. The calculation runs in your browser, and this page does not save or send what you type. The pedigree is written into the page address after the #, so it can appear in your browser history and in links you copy. Browsers do not send that part of an address to a server. Vercel Analytics and Speed Insights count a visit to this page without that part of the address, and the other analytics and advertising tools send nothing from this page.