How to use the Dog Age Calculator
- Enter your dog's age in years and months.
- Choose the size your dog is (or will be) when fully grown.
- Read the age in human years, and compare the size-based chart with the DNA formula and the 7-year rule.
Is one dog year really seven human years?
No. Dogs grow up much faster than people at the start: a one-year-old dog is roughly as mature as a 15-year-old teenager, and a two-year-old is like a person in their mid-twenties. After that, each dog year counts for about 4 to 7 human years, depending on size. Large and giant breeds age faster and have shorter lives than small breeds.
Dog years to human years chart
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 12 |
| 2 | 24 | 24 | 24 | 22 |
| 3 | 28 | 28 | 28 | 31 |
| 4 | 32 | 32 | 32 | 38 |
| 5 | 36 | 36 | 36 | 45 |
| 6 | 40 | 42 | 45 | 49 |
| 7 | 44 | 47 | 50 | 56 |
| 8 | 48 | 51 | 55 | 64 |
| 9 | 52 | 56 | 61 | 71 |
| 10 | 56 | 60 | 66 | 79 |
| 11 | 60 | 65 | 72 | 86 |
| 12 | 64 | 69 | 77 | 93 |
| 13 | 68 | 74 | 82 | 100 |
| 14 | 72 | 78 | 88 | 107 |
| 15 | 76 | 83 | 93 | 114 |
| 16 | 80 | 87 | 99 | 121 |
Small: up to 20 lb (9 kg). Medium: 21–50 lb. Large: 51–100 lb. Giant: over 100 lb (45 kg). Human-year equivalents from the size-based chart widely used by vets.
The DNA formula
A 2020 study from the University of California, San Diego compared chemical changes in the DNA of Labrador retrievers and people as they age. It suggested human age ≈ 16 × ln(dog age) + 31, where ln is the natural logarithm. By this measure, dogs age very quickly in their first years and slowly later. It was based on one breed, so the size chart is usually the better guide.
Every dog is different. Your vet can tell you more about your dog's life stage and the care it needs.
Frequently asked questions
How old is a 3-year-old dog in human years?
About 28 for small, medium and large dogs, and about 31 for giant breeds.
Why do big dogs age faster?
Large breeds grow quickly and tend to develop age-related problems earlier, so their life expectancy is shorter. Scientists are still studying exactly why.
What about cats?
Cats age differently: a 1-year-old cat is about 15 in human years, a 2-year-old about 24, and each year after that adds about 4.