Unfortunately there is no simple mathematic formula to calculate how long your dog will live, however, on average small dogs have a tendancy to live longer than larger dogs but it really also depends on the breed of dog. This is largely due to the fact that the bodies of larger dogs must work harder (are more stressed) than the bodies of smaller dogs and genetics have a role to play in determining the lifespan of different dog breeds.
Large medium to large breed dogs tend to live about ten years, although there are exceptions to every rule. Smaller breeds tend to live longer, anywhere from twelve to fifteen years.
Of course these figures are taking into consideration overall good health and quality care with regular check-ups with your local Vet during the course of your Dog’s lifespan. Genetics also play a vital role in longetivity, with some breeds tending to outlive others on average.
Recent advances in medical science have led to dogs having a much higher life expectancy than they did say, twenty years ago. Dogs can now be treated for cancer, tumours and various ailments which previously would have resulted in them living a far shorter life. It may not be possible to cure all dogs with serious illnesses, but many can have their life prolonged. In addition the majority of dogs are usually kept for pleasure and most are pets as opposed to having to work.