The second Straight Dope book described a better theory about the aging of a dog–the first year of a dog’s life equals 21 human years, and each year after that, four human years.
What about cats? Do they age in much the same pattern?
Looks like it, although Wikipedia has a slightly different take than what was presented in the book.
Cats generally live longer than dogs. Especially for bigger dogs.
Cats are sexually mature slightly earlier, but both under a year.
Almost 20 years ago when we adopted a cat I picked up a book about cats. It stated that the comparable aging for cats is 16-8-4-4…
The book could have been wrong or the science of cat could have updated.
I don’t know that there is a “right or wrong” here, for these sorts of rules. These are all rough approximations, intended for ease of mental calculation. The comparable human age for the age of an animal is not a linear function, and is probably also somewhat subjective, based on observing a lot of the animals and saying that an animal at x years seems to be about like a human at y years. It isn’t a good fit to a linear function, but it should be a smooth curve. These “stepped rules” are approximating the smooth curve as piecewise linear so that it’s easy to express and calculate.
I wonder - if we carefully collected a bunch of observational data on dogs or cats, saying “this x year old animal seems to be about like a y year old human”, what functional form would it fit well to? I suspect a second degree polynomial would fit the data reasonably well over the range we have, although it would NOT be an accurate description of the physical processes involved. But nobody wants to remember ax^2 + bx + c with odd-seeming values for a, b and c when trying to figure out how old rover or fluffy is in human terms.
This has always been my understanding.
One problem with these calculations is that cats seem more prone to age outliers than humans. The oldest known housecat lived to be 39. By the 16-8-4-4 rule, that’s 172 years. Most cats are lucky to live to 18 or so, and this one lived over twice that long. It’s a bit strange.
You should also factor in that cat’s don’t really get old. They stay reasonably spry till very near the end and suddenly pop their clogs - often from their kidney use-by date expiring.
I’ve read that it’s 7 years for the first 4, then 4 thereafter for small dogs, and 7 per year for larger dogs.
This site has a calculator for dog ages.
http://www.pedigree.com/all-things-dog/dog-age-calculator/default.aspx
Here’s one for cats.
Eric Gurney once came out with a book titled * How to Live with a Calculating Cat * (rendered in Spanish as Como vivir con un gato egoista). 
I don’t know about during development, but according to a chart in my vet’s office, domestic dogs and cats have essentially the same lifespan, it being a function of body weight more than anything else. The bigger they are, the faster they fall. Dogs and cats of the same weight tend to have the same lifespans.
I just don’t know many 150-lb domestic cats with which to test the extremes of this hypothesis.
I don’t want to know any 150 - pound cats either! :eek:
39 is crazy old, no doubt. It does seem that cats making it to 20 are not particularly uncommon. That makes me think that the 16-8-4-4 rule should probably start subbing in some 3s or 2s to replace some of those 4s after a few years. Perhaps even some 1s when the rare cat gets into their mid-20s.
Just for fun, I’m throwing in a domestic rabbit range: 21-6-6… . Bunny number two (long gone) was approx. 77 YO when we had to put him down, but would have gone longer; the disease that crippled him was not life threatening, but the complications called for euthanasia. Pet rabbits are living much longer than they were even ten years ago, so that range will most likely need to be doctored eventually.
yabob, good posting; I can’t wait to throw that polynomial formula at the vet next time I see him. 