Dog Age Calculator
Turn your dog's age into human years — and see why a Great Dane ages faster than a Chihuahua.
Size matters
Bigger dogs age faster after age two, so this calculator asks for your dog's size, not just its age.
An estimate
The result is an approximation. Breed, genetics, and health all shift the real figure.
How old is my dog in human years?
A size-aware estimate, not the old times-seven myth
A dog's age in human years is an estimate of how far through life your dog is, mapped onto a human lifespan. According to the American Kennel Club, dogs mature fast in their first two years and then age at a pace that depends on their size — so a one-size-fits-all multiplier gets it wrong. This calculator uses the size-aware AKC approximation instead.
The first year of a dog's life counts for about 15 human years, and the second year adds roughly 9 more — so a two-year-old dog is about 24 in human terms. After that, each extra year adds a size-dependent amount: +4 for small dogs, +5 for medium, +6 for large, and +7 for giant breeds.
Human = 24 + (dog years − 2) × size factorThe size factor is what makes this accurate: large and giant breeds pack more ageing into each calendar year, which is why they tend to have shorter lifespans than small dogs.
Suppose your dog is 5 years old and a medium breed, such as a Border Collie.
Start at age two
By its second birthday a dog is already about 24 in human years.Count the years after two
5 − 2 = 3 years remain, each adding the medium size factor of 5.Add it up
24 + 3 × 5 = 39, so a 5-year-old medium dog is about 39 in human years.
The number tells you roughly which life stage your dog is in — puppy, young adult, middle age, or senior. The key insight is that bigger dogs age faster: at the same calendar age, a giant breed lands at a higher human age than a small one, which is why large dogs are considered seniors earlier. The old "one dog year equals seven human years" rule is inaccurate, according to the AKC — it overstates early ageing and ignores size entirely. Treat the figure as a friendly guide to your dog's life stage rather than a precise age.
The arithmetic is exact, but the mapping from dog years to human years is only ever an approximation.
Every dog is different
This calculator is for informational and fun purposes only. Real ageing varies with breed, genetics, diet, and health, and the size bands are broad averages rather than firm cut-offs. For anything to do with your dog's health or life expectancy, consult a veterinarian.