Q&A: Is 1 of our years really 7 of a dog's?

Q: What's the best way to estimate my dog's age in human years? And how long can pets live?

A: It would be great if there were an easy formula for figuring out a pet's age "in people years," but many variables affect the rate at which a dog or cat ages, including size, breed and environment. For instance, outdoor cats face more hazards than indoor cats, so their nine lives may not last quite as long.

Pets mature rapidly during their first two years, and then the rate at which they age slows down. Instead of multiplying by seven for dogs, think of a 1-year-old dog as equivalent to a 12-year-old child. By the time he's 2 years old, the dog has bounded into adulthood, with a human-equivalent age of 24 years. For every year after that, add four years.

We can all agree that pets don't live long enough. A few outliers live to be 20 years or more, but that's rare. Many pets are living to be 15 or older, and size seems to be the determining factor. Toy breeds and cats tend to have the longest life spans, often living well into their teens. Some giant breeds live to be only 6 or 8 years old. Good genes, good nutrition and good weight management also influence longevity. If you're buying a puppy from a breeder, ask how long her dogs usually live. Dogs who aren't allowed to get fat live an average of two years longer than those who pack on the pounds.