How this pet age calculator works
Dogs and cats do not age at a steady rate, and they certainly do not age at seven human years per calendar year. They grow up extremely quickly, reaching the rough equivalent of human adolescence within their first year, then their ageing slows down. To stay accurate this calculator uses a staged formula rather than a single multiplier.
The first year of life counts as about 15 human years, and the second year adds about 9 more, bringing a two-year-old pet to roughly 24. From the third year onward, each additional pet year adds a smaller, steady amount: about 4 years for a cat, and for a dog an amount that depends on size — roughly 4 for small breeds, 5 for medium, 5.5 for large and 6 for giant breeds, because bigger dogs age faster and live shorter lives.
| Pet age | Cat (human yrs) | Medium dog (human yrs) |
|---|---|---|
| 1 | 15 | 15 |
| 2 | 24 | 24 |
| 3 | 28 | 29 |
| 4 | 32 | 34 |
| 5 | 36 | 39 |
| 6 | 40 | 44 |
| 7 | 44 | 49 |
| 8 | 48 | 54 |
| 9 | 52 | 59 |
| 10 | 56 | 64 |
| 11 | 60 | 69 |
| 12 | 64 | 74 |
| 13 | 68 | 79 |
| 14 | 72 | 84 |
| 15 | 76 | 89 |
Reference note: these figures are general estimates for healthy pets. Individual breed, weight, diet and health all affect ageing, so use the result as a guide and rely on your veterinarian for medical decisions.
Frequently asked questions
- How old is my dog in human years?
- A dog's first year is roughly 15 human years and the second adds about 9, for 24 by age two. After that each dog year adds a size-based amount — about 4 for small breeds and up to 6 for giant breeds — so a 5-year-old medium dog is around 39.
- How old is my cat in human years?
- A cat's first year is about 15 human years, the second adds about 9 (24 total), and each year after adds roughly 4. So a 3-year-old cat is about 28 and a 10-year-old cat is about 56.
- Is one dog year really seven human years?
- No — that's a myth. Dogs mature very fast in their first two years and then age more slowly, so a flat seven-times multiplier is inaccurate. A staged formula that front-loads the early years is much closer to reality.
- Do big dogs age faster than small dogs?
- Yes. Larger and giant breeds age faster and have shorter lifespans, so each adult year counts for more human years — about 4 for small dogs rising to about 6 for giant breeds.
- How do I calculate cat years?
- Count 15 human years for the first year, 9 for the second (24 total), then add about 4 for every additional year. A 7-year-old cat is roughly 24 plus five years at 4 each, or about 44 human years.
- When is a dog or cat a senior?
- Most cats and small-to-medium dogs are considered senior from about 7 years, while large and giant dogs get there earlier, around 5 to 6 years. Before that they pass through a young-adult phase after puppyhood or kittenhood.