How it works
The “one dog year equals seven human years” rule is a myth. Dogs mature very quickly in their first two years, then age more slowly, and larger breeds age faster than small ones.
This calculator uses the size-based chart commonly shared by veterinarians and the American Veterinary Medical Association: a dog’s first year is roughly 15 human years, the second adds about 9, and each year after adds about 4 to 7 depending on size. Partial years are interpolated.
For comparison, it also shows a 2020 estimate from a UC San Diego study of DNA methylation in Labrador retrievers: human age ≈ 16 × ln(dog age) + 31.
Formula
Year 1 ≈ 15, year 2 ≈ 24, then about +4 (small) to +7 (giant) per year
Questions people ask
Why do large dogs age faster?
Large and giant breeds have shorter average lifespans and reach senior status sooner, often around 6 to 7 years, compared with 10 or more for small breeds. The exact reasons are still being studied.
When is a dog considered a senior?
Roughly the last quarter of its expected lifespan. For many small dogs that is around 10 to 12, and for giant breeds as early as 5 or 6.
Is the 7-year rule ever right?
Only by coincidence for some middle-aged medium dogs. It badly underestimates young dogs: a 1-year-old dog is closer to a 15-year-old human.