Why "one dog year = seven human years" is wrong
Dogs grow up much faster than people at the start of life: a 1-year-old dog is physically and sexually mature, more like a human teenager than a 7-year-old child. After that, aging slows down — and it depends on size. Small dogs generally live longer and age more slowly in later life than large and giant dogs.
How we calculate
We use a widely used size-based chart: the first year of a dog's life equals about 15 human years, the second year adds about 9 more (so a 2-year-old dog is about 24), and each year after that adds roughly 4–5 years for small dogs, 5–6 for medium dogs, 6–7 for large dogs and 7–8 for giant dogs.
For comparison, we also show the result of a 2020 formula from researchers at the University of California San Diego, based on DNA methylation changes in Labrador Retrievers: human age ≈ 16 × ln(dog age) + 31. It was developed in one breed, so treat it as an interesting comparison rather than a rule.
Life stages
| Stage | Typical age |
|---|---|
| Puppy | Birth to 6–12 months |
| Young adult | Until 2–3 years |
| Mature adult | Until the last 25% of expected lifespan |
| Senior | Last 25% of expected lifespan (often 7–10 years, earlier in giant breeds) |
| End of life | Final stage |
Senior dogs benefit from vet check-ups every 6 months. See caring for a senior dog.