Dog Years Calculator

Enter your dog's age and size. The calculator uses the popular veterinary rule of thumb: 15 human years for the first dog year, 9 for the second, then about 5 per year after that — adjusted slightly by size, because large dogs age faster and small dogs slower. See the dog lifespan & health overview for the full longevity picture.

This is the widely used estimate, not a lab measurement of your individual dog. For health decisions, your vet's judgment beats any calculator.

Is one dog year really seven human years?

No — that's the myth this calculator replaces. Dogs age fast early on (about 15 human years in year one) and then slow down, which is why a 2-year-old dog is roughly 24 in human years, not 14.

Why does size change the result?

Big dogs age faster than small ones once they're adults. After the first two years, large breeds add roughly 6 human years per dog year while small breeds add about 4 — one reason small dogs tend to live longer.

How accurate is this calculator?

It's the standard rule of thumb vets and researchers quote — good for birthdays and curiosity, not for medical decisions. Your vet knows your individual dog; this doesn't.