How long do dogs live, and how do dog years work?

Lifespan depends strongly on size and breed: small dogs such as Chihuahuas often live 14 to 16 years, while giant breeds like Great Danes average only 7 to 10. The American Veterinary Medical Association suggests the first year of a medium-sized dog’s life equals about 15 human years, the second about 9, and each year after that roughly 4 to 5. A 2019 study at the University of California San Diego compared DNA changes in dogs and humans and found similar fast early ageing. Mixed-breed dogs tend to live slightly longer on average than purebreds. Good diet, a healthy weight and regular vet care can add years to a dog’s life.