Ask This Librarian – Dog years

Today’s question, from a friend who just put a much beloved elderly pet to sleep:

I found out from a chart at the vet’s that Kelty, a 15-year-old Chow/Malamute mix, was, in human years, 99 years old! I want to know how the idea of “dog-years” got started, who figures it out, what kinds of information is added to the mix when they decided how it worked, etc. All about it…

My answer below…

My answer:

The history of the one dog year equals seven human years isn’t clear, but there’s a great Examiner article on that goes into more of the background history at . According to that article, the 1:7 equation became popular due to a series of Alpo dog food commercials in the 1970s.

In terms of figuring it out, every source I’ve found is very clear that it’s an art, not a science. The main factor is the breed of the dog, and other factors like the size of the dog also play a role (so a mixed breed dog would look at the dog’s overall size and build).  Other factors include gender, neutering, and the animal’s individual history.

In terms of data, many charts give a best estimation. A veterinarian, Dr. Kelly Cassidy, created a website at that pulls together data from several large studies in multiple countries, to try and give a best guess for common breeds.

Some sites say that it varies depending on the age of the dog (i.e. that the first two years of a dog’s life are equal to 10.5 years, and then it drops down from there.) However, more detailed research (as above) doesn’t seem to support that. The Wikipedia page on aging in dogs has some additional information about this at .They also include some details on common breed lifespans.

Calculating is therefore a little tricky, but there’s a great chart at that helps make it easier. (Follow the color for the size of dog: large dogs are on the outside of the circle, middle sized dogs in the middle, and small dogs on the inside.)

I’ll come back to the second part of your question – different advice on when you might be ready to look at another dog – in the next few days.

My process:

A little quick Google searching showed me that there were a lot of people with opinions out there, but didn’t immediately turn up answers to the question about where the idea came from, or more detailed information on how it’s calculated.

I took a look at Wikipedia, which had a fairly detailed article, but which also had excellent links to most of the pages referenced above, including the Slate article. From there, it was easy to find reasonable sources for much of the information.

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Hi, I’m Jen

Librarian, infovore, and general geek, likely to write comments about books, link collections, and other thoughts related to how we find, use, and take joy in information.

I'm the Research Librarian at the Perkins School for the Blind

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