Dog Days Are On

When I was a kid we were told that 1 dog year was equivalent to 7 human years. This was based on 1) an average dog lifespan of 10 years, 2) an average human lifespan of 70 years, 3) a desires to convince children that their dog had lived a long and happy life.

I figured that both of these figures are now well out of date, so I wondered what the correct modern figure would be.

First, on the human side, average lifespan has gone up from ~70 in the 1960s to almost 80 in the 2020s.

If dog lifespans had remained unchanged, this would make a dog year equivalent to 7.7 human years.

For dog life expectancy, I was delighted to stumble on the 2023 paper "Life expectancy tables for dogs and cats derived from clinical data" from Frontiers of Veterinary Science. Incredibly, they had a dataset of 13 million dogs:

(If you're wondering about your own pet, I converted this into a life expectancy calculator for dogs, and another one for cats)

The average life expectancy for dogs in general was 12.69; dog lifespans have increased more than human lifespans have in the relevant period. As a result, even with the increase in human life expectancy, a dog year in 2025 should more accurately be referenced as "6.1 human years", or 6 years if you're rounding.

That said, I suspect there's a huge bias in the fact that this data was collected by a pet hospital. This means stray dogs would be excluded, though maybe that's less of a problem to the extent that the dog-year calculation is intended for children who have a specific pet in mind, but it also excludes people who never take their pet to the vet (or who only take their pet to the vet once, etc).

There's lots of variation in life expectancy by dog size: going from 9.5 years for giant, 11.5 years for large ones, 12.7 years for medium dogs, 13.5 years for small, but reversing slightly to 13.4 years for toy dogs. I don't really understand this: across species, big animals live longer (in general), but within a species (apparently) big animals live shorter. I found a paper on this but I didn't really understand it, if any of you do please throw your thoughts in the comments.

In other news, dog and cat life expectancy have both increased meaningfully even just between 2013 and 2019:

Why the increase in life expectancy? I'm speculating wildly here, but my bets are on two things. I think pet food has increased in quality a ton since I was younger: you can frame this in a positive way, but the negative frame is that I fear our old-school pet food was (in some sense) poisoning our pets.

Second, castrated animals tend to live longer [citation needed], and I wonder if there's more neutering and spaying these days.