Dear Doctor – How old is old?

Letter to Tufts Veterinarians


Q Is it really seven human years for every dog year?
Dave Rhodes
Dearborn Heights, MI

Dear Mr. Rhodes,
A The 7-to-1 ratio is not an unreasonable guide for mid-sized dogs — those who weigh somewhere between 20 and 50 pounds. But large dogs, including Labrador Retrievers and Collies, age more quickly, while small dogs, such as Havanese and Chihuahuas, age more slowly.

So, for example, a 6-year-old Cocker Spaniel who weighs 30 pounds could be considered the equivalent of about 42 years old. But a 6-year-old Labrador Retriever who weighs 70 pounds is biologically older — more on the order of 45 human years. A 6-year-old Pug weighing fewer than 20 pounds, on the other hand, is closer to 40 in human years. If the dog is a giant breed, like a Newfoundland, at 6 she will be around 49.

This is why the bigger the dog, the shorter, on average, her lifespan will be. Only 13 percent of giant breeds live at least 10 years. But almost 40 percent of dogs who weigh fewer than 20 pounds live 10 years or longer (sometimes as long as 20 years).

We say on average because just like with people, biological age and chronological age do not always match up. Some people in their 70s still go white water rafting, while others are hobbled by illness, and so it goes with dogs. We’ve cared for dogs in their teens who had so much energy you’d think they were no older than five. At the same time, we’ve taken care of 5-year-olds slowed down by arthritis, diabetes, and other conditions typically associated with old age. In other words, although chronological age is fixed, biological “old” age can be hard to pigeonhole.

We suggest that people not drive themselves crazy trying to figure out how old their dog is in human years or worrying over how long their dog will live. Instead, use your dog’s size as a guide for when she will need increased veterinary monitoring so that she will remain as healthy as possible for as long as possible. When a dog becomes geriatric, a vet may not only suggest that you bring her in for checkups more often, she or he may also start ordering different screening tests to check for various ills that begin to creep in during old age.

The following chart gives good rules of thumb for when your dog will be at the right age for the vet to start assessing her health requirements a little bit differently. Even these are not numbers you should get hung up on, however. As we said, some dogs are young for their age, some old. You and your vet will be able to tell.


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