Inbreeding calculators (COIs)

Two puppies sitting together

What is inbreeding?

Inbreeding occurs when puppies are produced from two related dogs, i.e. dogs with relatives in common. High levels of inbreeding can affect the health of these puppies, although it is difficult to know the exact impact it can have. In general, we do know that the higher the degree of inbreeding, the higher the risk is of the puppies developing both known and unknown inherited disorders. Inbreeding can also have an impact on the breed as a whole, e.g. reducing litter sizes and fertility.

You can find out more about inbreeding, genetics and DNA testing in a number of films available on The Kennel Club Academy.

Measuring the degree of inbreeding

The degree of inbreeding can be measured using a calculation called the coefficient of inbreeding (CoI), or inbreeding coefficient. This calculates the probability that two copies of a gene variant have been inherited from an ancestor common to both the mother and the father. The lower the degree of inbreeding, the lower the inbreeding coefficient.

Using our inbreeding coefficient calculators

When choosing a potential mate, we recommend you use our Inbreeding Coefficient calculators as part of your decision. These use all the pedigree records stored on our database to calculate a result.


How many generations of pedigree information are used?

Our CoI calculators use all available, electronically held, pedigree information and they do not limit the number of generations used. This makes each calculation as precise as possible.

What does your result mean?

The CoI calculator gives you a percentage score. In general, the lower the percentage, the lower the degree of inbreeding.

To put your result into perspective:

  • 0% = a dog with two apparently unrelated parents (based on all available pedigree information)
  • 12.5% = the genetic equivalent of a dog produced from a grandfather to granddaughter mating, or the mating of a half-brother/sister
  • 25% = the genetic equivalent of a dog produced from a father to daughter mating, or the mating of full-brother/sister
  • More than 25% - inbreeding is accumulative, so if it has occurred to a significant degree over several generations, the inbreeding coefficient may exceed 25%

Breeding advice

Where possible, you should produce puppies with an inbreeding coefficient which is at, or below, the breed average and ideally as low as possible. This average is shown to you each time you use our CoI calculators.

If a breeder DNA tests their dogs, they are taking steps to avoid a known risk. By using CoI calculators when selecting potential mates, they are reducing the risk of unknown conditions.

How is the breed average calculated?
Each CoI calculation is accompanied by a breed average. This number helps you compare any potential matings to the average of the breed’s current population and puts that CoI into perspective.

This breed average is calculated each June. First, we calculate the CoI of all dogs in the breed using all available electronically held pedigree information. We then calculate the average of those CoIs for the dogs that were registered with The Kennel Club born in the UK during the previous year. Comparing the CoIs of a litter you may be planning to the current breeding population is a more effective way of reducing inbreeding than by comparing it to an average of both living and historic dogs.

The CoIs of historic dogs born many years ago may be generally higher than the current breed average. This suggests that inbreeding levels in the breed as a whole are decreasing. It is possible that the CoIs for some of those historic dogs, although higher than the current breed average, may have fallen below the average of dogs living at the time and could have met with breeding guidance given.

In smaller breeds, if no dogs have been born in that year, the breed average will default to the last year in which a calculation could be performed. In breeds where there is no available breed average data for the past five years, the annual breed average will display as N/A. This may include breeds where no dogs have been born in the UK for five years or more, or some newly recognised breeds.

Check the number of generations 

For dogs that have been imported, we may only have a three generation pedigree, so it may be difficult for us to calculate an informative CoI. 

  • When using our CoI calculators always check the “about this calculation” section to see how many generations have been used for calculation
  • If this indicates that only the first three generations are fully complete, you may wish to use the CoI result with care
  • If additional pedigree information or inbreeding resources are available to you, then you may wish to consult these

Remember it's a measure of risk

It is important to note that the inbreeding coefficient is a measure of risk, rather than a direct measure of health. It is possible that two closely related dogs do not have the same autosomal-recessive genes, while two seemingly unrelated dogs do - it's all down to chance. Although the CoI is not a guarantee of health, it is a measure of risk with a higher CoI suggesting a higher risk.

Making balanced breeding decisions

As well as considering the implications of a dog’s inbreeding coefficient, there are other equally important factors to consider when deciding whether two dogs should be mated together, such as temperament, genetic diversity, conformation, other available health test results, the general health of the dogs etc. Your breeding decisions should always be well balanced and take into consideration the qualities and compatibility of both the sire and dam that you are considering.

Questions and answers

Can CoIs guarantee the health of future puppies?

Breeders should be aware that the inbreeding coefficient is a measurement of risk and does not guarantee that puppies produced will, or will not, have any inherited health conditions. The higher the inbreeding coefficient, the higher the risk of health issues.

Will The Kennel Club still register puppies with a higher than average inbreeding coefficient?

The Kennel Club will still register the puppies of a mating which results in an inbreeding coefficient which is higher than the breed average, but it is recommended that you consider a different pairing, all other considerations being equal. If you do go ahead with the mating and plan to use any of the puppies for breeding in the future, it is strongly recommended that you take extra care to choose a highly unrelated mate that will result in puppies with an inbreeding coefficient well below the breed average.

To help reduce the highest degrees of inbreeding, The Kennel Club does however not register puppies produced from a mating between father and daughter, mother and son, or brother and sister, save in rare exceptional circumstances for scientifically proven welfare reasons.

Where can I find out more about inbreeding?
You can find out more about the impact of inbreeding in our understanding canine genetics area.