Dog age calculator

Human-equivalent age from the 2020 DNA-methylation study, which replaced the “multiply by seven” rule with something that was actually measured.

Human-equivalent age

Enter an age of one year or more.

Why “times seven” was always wrong

The seven-year rule appears to have come from dividing a rough human lifespan by a rough dog lifespan and stopping there. It fails at both ends and in an obvious way: a one-year-old dog is not a seven-year-old child. It can reproduce, it has a full set of adult teeth, and it is close to its adult size. A seven-year-old human is none of those things.

Dogs age fast early and then slow down. Any straight-line rule has to be wrong at one end to be right at the other.

What the 2020 study did instead

Researchers compared how DNA methylation — chemical marks that accumulate on the genome in a fairly clocklike way — changes over time in dogs and in humans, then matched the two curves. The relationship they published is logarithmic:

human equivalent = 16 × ln(dog age in years) + 31

That shape matches what owners observe. The first year covers an enormous amount of development; the gap between years eight and nine is far smaller.

The known limit of this formula. It was fitted to a population of Labrador Retrievers. Size affects canine ageing strongly and in a direction opposite to most mammals — small dogs generally live longer than large ones — so a Chihuahua ages more slowly than this curve implies and a Great Dane faster. There is no published breed-specific version of the equation, and inventing one by tweaking the constants would be making up precision that does not exist.

Puppies

The formula starts at one year, and this calculator refuses to extrapolate below that rather than returning a confident wrong answer. Development in the first year is too fast and too size-dependent for a single curve to describe.

Sources: Epigenetic ageing curve: Wang et al., Cell Systems 2020