This dog age calculator converts your dog’s age into human years. It uses the size-based chart published by veterinary groups, because large dogs age faster than small ones, and compares it with the newer UC San Diego DNA formula and the old “multiply by 7” rule.
Why the 7-year rule is wrong
Dogs mature much faster than people in their first two years: a 1-year-old dog is roughly like a 15-year-old human, and a 2-year-old like a 24-year-old. After that, ageing slows, but larger breeds age faster than small ones.
Dog years to human years by size
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 4 | 32 | 33 | 35 | 37 |
| 6 | 40 | 42 | 45 | 49 |
| 8 | 48 | 51 | 55 | 64 |
| 10 | 56 | 60 | 66 | 78 |
| 12 | 64 | 69 | 77 | 93 |
| 14 | 72 | 78 | 88 | 108 |
| 16 | 80 | 87 | 99 | 123 |
Small: 20 lb or less. Medium: 21–50 lb. Large: 51–90 lb. Giant: over 90 lb.
The DNA formula
A 2020 study from the University of California, San Diego compared chemical changes in DNA (methylation) in Labrador retrievers and people. It proposed: human age = 16 × ln(dog age) + 31. By this formula, a 5-year-old dog is about 57 in human years. Because it was based on one breed, it suits medium and large dogs best.
Frequently asked questions
How old is my dog in human years?
A 1-year-old dog is about 15 in human years and a 2-year-old about 24. After that, add about 4 to 5 years per dog year for small and medium dogs and more for large and giant breeds.
At what age is a dog a senior?
Often around 7 for many breeds, earlier for giant breeds and later for small breeds. Your vet can advise on senior check-ups.
Why do big dogs age faster?
Larger breeds tend to have shorter lifespans and show age-related changes earlier, though the reasons are still being studied.
Which method is most accurate?
Neither is exact for every dog. The size chart reflects breed size; the DNA formula is based on Labradors. Health and genetics matter too.
Related calculators
Sources
- Chewy: Dog years to human years (AAHA size chart)
- Sci.News: Wang et al., Cell Systems (2020), dog-to-human ageing formula
Last reviewed: October 2026. For information only; results are estimates; check important figures with a professional.