The ×7 Rule Is a Myth
Dogs don't age at a constant rate. A one-year-old dog is roughly a human teenager (~15 human years), and a two-year-old about 24 — after that, each dog year adds roughly 4–7 human years depending on size. This calculator uses that veterinary consensus curve with size adjustments.
Size Changes Everything
Unusually among mammals, bigger dogs age faster. A 10-year-old Chihuahua is like a human of ~56; a 10-year-old Great Dane closer to ~72. Life expectancy follows: small breeds often reach 14–16 years, giant breeds average 7–10.
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 year | 13 | 15 | 17 | 19 |
| 5 years | 36 | 39 | 42 | 45 |
| 10 years | 56 | 64 | 72 | 80 |
The Science Behind It
A 2020 UC San Diego study of DNA methylation ("epigenetic clocks") in Labradors found aging is fastest in the first two years and slows dramatically after — matching the curve this calculator applies. Researchers proposed the formula human_age ≈ 16 × ln(dog_age) + 31 for Labradors; our size adjustment extends the idea across breeds.
Life Stages
Puppy (to ~1 year), young adult, adult, then senior — small dogs turn "senior" around 10–12, giants as early as 5–6. Senior status mainly means twice-yearly vet checks and watching weight and joints, not slowing down the walks your dog still loves.