| We veterinarians are often asked to compare the age of a cat in "cat years" to its equivalent in "human years." Although this exercise has long been attempted using one formula or another, there is no scientifically reliable method for converting the age of one species into the age of another.
One piece of information still lacking for the general cat population is accurate mortality information: At what age, and from what, do cats die? The most frequently cited causes of death in elderly cats are kidney failure, cancer and infectious disease. But this does not count all the young cats who die in car accidents and for other reasons.
Environment certainly plays a role in life expectancy. We do know that the average lifespan of feral tomcats (that is, intact male cats who live in the wild) is quite brief-about three years-while the average lifespan of a neutered indoor pet cat can extend to the late teens or even 20 years. Because feral cats are exposed to infectious diseases (probably without the benefit of vaccination), automobiles, dogs and other hazards, it is understandable that their average lifespan would be relatively short.
Genetics also has a role to play. Mixed-breed cats have been reported to be hardier, and there may be some truth in this. Inbred cats, and cats bred within a small gene pool, are more likely to have inherited problems, and therefore may not live as long, as a group. On the other hand, pedigreed cats from responsible breeders are carefully matched to avoid genetic problems in breeding, while mixed-breed cats tend to have been bred randomly. Genes also play a role in the tendency to develop certain diseases-or the luckier tendency to avoid them.
Given these caveats, is there a roughly accurate age conversion formula? The old, outdated idea was that one human year is equivalent to seven cat years. But a one-year-old cat is more physically and behaviorally mature than a seven-year-old child. So the following "rules of paw" are considered to be more accurate: The first two years of a cat's life are roughly equivalent to the first 25 years of human life; thereafter, each calendar year is roughly equivalent to four feline years.