Dear Cameren,

Humans have kept dogs as pets for more than 14,000 years. That close friendship inspires scientists to explore questions like yours.

I talked about how dogs age with my friend Ryan Baumwart. He’s a heart doctor for dogs. He teaches in the veterinary hospital at Washington State University.

I asked Baumwart if a dog year is equal to seven human years.

“I think it’s a good general rule,” he said. “But some larger breed dogs like bullmastiffs and Great Danes have a shorter lifespan of 6 to 8 years. So if you do the math, they get shorted. Then some small breed dogs like Chihuahuas seem to live forever.”

Baumwart told me most puppies reach their full height at about 6 months old. That’s also when their adult teeth come in. Then they start filling out and growing wider. Most dogs are fully grown at about 1 year old. They’re considered geriatric, or old, at about 7 years old.

That fits with the guidelines used by the American Kennel Club and American Veterinary Medical Association. They say the first year of a dog’s life equals 15 human years. The second year equals 9 human years. After that, each year equals 5 human years.

A full-grown German Shepherd walks toward the viewer, carrying a large stick. A German Shepherd puppy runs by its side.

Some researchers say they figured out a more precise calculation. Mammal DNA changes a little bit as we get older. Scientists can use these tiny changes to map how dogs age. You can use a special calculator to figure out your dog’s age using their method. If you love math, you can use their formula: multiply the natural logarithm of your dog’s age by 16 then add 31. The method relies on Labrador Retriever data. It may not work well for very small or very large dogs.

If you wonder why smaller dogs tend to live longer, you’re not alone. Scientists wonder that, too. Baumwart says we simply don’t know the answer yet.

We do know genes play a role in life span. Mixed breed dogs usually live longer than purebred dogs. Purebred dogs are more likely to inherit genetic diseases.

Lifestyle and environment also make a difference. Dogs need exercise and a healthy diet. Baumwart said to choose dog food that meets the guidelines set by the World Small Animal Veterinary Association (WSAVA). He recommends talking with your veterinarian about dog food and other questions about your dog’s health. They can tailor their advice to your specific dog.

Right now, Baumwart is part of the Dog Aging Project. The goal is to figure out how to help dogs live longer, healthier lives. The project will collect data from tens of thousands of dogs over 10 years. They’re also testing a medicine called rapamycin that makes mice live longer. They want to know if this medicine could help dogs—and maybe even humans—live longer.

That’s paws-itively awesome news for dogs and the people who have loved them for thousands of years.


Dr. Universe