Is it True That Small Dogs Live Longer Than Big Dogs?

This would seem like a very easy question to answer, but in reality it is not. There are many variables and the scientific data when scrutinized is conflicting. One can find scientific reports that claim the average dogs lifespan is anywhere from 10 to 13 years of age. The studies are imperfect at best, often relying on owners reports of dog ages which are not verifiable.

However, there are some generalizations that can be made.  Most of the longest-lived breeds are small; most of the short-lived breeds are large. However, not all small breeds are long lived. Many small breeds have median longevities between 9-11 years. Most large breed dogs have median longevities of less than 8 years; many breeds in 80+ pound group have median longevities between 9-12 years.

In all studies where pure bred dogs were compared to mixed breed dogs, mixed breed dogs live on average a year longer than purebred dogs. Dogs in the UK surveys report an average lifespan for all dogs being one year longer than for the surveys for the US and Canada.

Most of the research indicates that weight of the dog is the critical factor and heavier breeds tend to have shorter life expectancies.  This is somewhat in conflict with age expectancies as a general rule for most animal groups. In general the larger, heavier mammals live longer. Compare the lifespan of a mouse versus that of an elephant. In bird species it appears to be the same. A parakeet lives a much shorter life that a macaw. 

In dogs, the smaller breeds tend to mature earlier compared to the larger ones. However their aging process seems to slow down when compared to the aging process in the larger breeds. The old story that one human year equals seven dog years, is a very broad generalization that really is quite inaccurate. The aging process is not linear but rather exponential. The beginning of all dogs’ lives when compared to human development is much faster in the first few years but slows considerably over their later years.

So the answer to the question is yes, small breed dogs tend to live longer than large breed dogs. Unfortunately, the joy of dog companionship is always tempered by one thing- our beloved pets do not live as long as we do.