How Old Is a 3-Year-Old Dog in Human Years?
| Size | Human age | Life stage |
|---|---|---|
| Small ≤ 9 kg | 28 | Mature adult |
| Medium 9–23 kg | 29 | Mature adult |
| Large 23–45 kg | 30 | Mature adult |
| Giant > 45 kg | 31 | Mature adult |
By the veterinary rule of thumb used by the AVMA, a dog's first year equals about 15 human years and the second adds about 9, so every dog is roughly 24 at the age of two. After that the pace depends on size: small dogs add about 4 human years per calendar year, medium dogs about 5, large dogs 6 and giant breeds 7. For a 3-year-old dog that gives 28 (small), 29 (medium), 30 (large) and 31 (giant).
A 2020 study from the University of California San Diego compared DNA methylation in 104 Labrador Retrievers with humans and proposed the formula human age = 16 × ln(dog age) + 31. By that formula a 3-year-old dog is about 49. It was derived from a single breed, so it is shown here for comparison rather than as the main estimate.
Ad
Discover your destiny!Tarot MagicTarot card readingsStart Reading ✦Frequently Asked Questions
How old is a 3-year-old dog in human years?
About 28–31 human years: 28 for a small dog, 29 for a medium dog, 30 for a large dog and 31 for a giant breed.
Is a 3-year-old dog a senior?
Under the simplified AAHA life-stage scheme a dog becomes a senior at about 7 if it is small or medium, at 6 if large and at 5 if giant. At 3: small, medium, large, giant — mature adult.
Is one dog year really seven human years?
No. The "×7" rule is a myth: dogs mature much faster in the first two years and then slow down, and large breeds age faster than small ones. By the ×7 rule a 3-year-old dog would be 21; the size-based estimate gives 28–31.
How do I work out my own dog's age?
Use the calculator on the main dog age page: enter years and months and pick your dog's adult weight. It also covers puppies month by month.