How to Calculate Dog Age in Human Years
The size-based method for converting a dog's age into human-equivalent years, with a worked comparison across sizes.
Converting a dog's age accurately means looking up where that age falls on a size-specific curve, not applying one flat multiplier to every dog.
Worked comparison
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 year | 15 | 15 | 14 | 12 |
| 5 years | 36 | 36 | 45 | 45 |
| 10 years | 56 | 60 | 78 | 78 |
| 15 years | 76 | 83 | 115 | 115 |
The gap between small and giant breeds widens dramatically with age — by 15 years old, a giant breed's human-equivalent age is nearly 40 years higher than a small breed's, reflecting giant breeds' typically shorter lifespans.
For ages between whole years
The Dog & Cat Age Calculator interpolates smoothly between whole-year values, so a 3.5-year-old dog gets a proportionally blended result between the age-3 and age-4 values rather than rounding to the nearest year.