Pet Age Calculator
How it works
The first year of a dog or cat's life counts as 15 human years — most of their physical growth happens in that time. The second year adds another 9, bringing a two-year-old pet to 24. After that, each additional year adds a flat amount: 4 human years for cats and for small or medium dogs, or 5 for large dogs, since bigger dog breeds are documented to age faster once they are past their first couple of years.
Frequently asked questions
Why do the first two years count for so much more?
Most of a dog or cat's physical development — reaching sexual maturity, finishing most of their skeletal growth — happens in their first two years of life, a real and well-documented pattern rather than something this tool invents. That is why year one alone is worth 15 human years and year two adds another 9, while every year after that adds a much smaller, flat amount.
Why does size matter for dogs but not cats?
Larger dog breeds are well documented to have shorter lifespans and to age faster in their later years than small breeds, so this calculator adds human years a bit faster per year for large dogs once they are past two years old. Cat breeds don't show that same size-linked difference in aging, so size is not a factor for cats.
Is this an exact biological formula?
No — it's a widely-used approximation, not a precise measurement of any individual animal. An individual pet's health, breed and genetics all affect how it actually ages; this gives a reasonable estimate to compare against, not a veterinary diagnosis.