Dog Age Calculator
Your dog's age in human years, adjusted for size.
Converting dog years
Set your dog's size class and age; the calculator returns the human-equivalent age with a life-stage note, plus the full chart across all sizes. The first year counts about 15 human years, the second about 9, and each year after that 4โ7.5 depending on size โ because big dogs age faster, a fact with real veterinary consequences.
Seven was always wrong
The multiply-by-seven rule fails at both ends: a one-year-old dog is a teenager, not a seven-year-old child, and a 15-year-old chihuahua is not 105. Size is the missing variable โ Great Danes are seniors at 7 while small terriers commonly reach 16 โ and the size-class chart here is the convention vet practices actually use for life-stage guidance.
The science took a turn in 2019: a UCSD team matching DNA methylation between species proposed human_age = 16 ร ln(dog_age) + 31, by which a one-year-old Labrador is biologically ~31 and ageing then slows sharply. Derived from one breed, it is not yet a practical everyday chart โ but it confirms the shape: dogs age fastest young. Either way, this is a fun approximation rather than veterinary advice. The cat version is next door, and the human age calculator handles your own birthday arithmetic to the day.
Frequently asked questions
How old is my dog in human years?
Roughly 15 human years for the first year, 9 for the second, then 4-7.5 per year depending on size. A 5-year-old medium dog is about 39 human years.
Is one dog year really seven human years?
No โ the rule is wrong at both ends. Dogs mature extremely fast early, then age at a rate that depends strongly on size.
Do small dogs really live longer than big dogs?
Yes, markedly: small breeds commonly reach 14-16 while giant breeds average 7-9. It is one of the odder facts in mammal biology, since across species bigger usually lives longer.
When is a dog a senior?
Roughly 7 for large and giant breeds, 9-10 for small ones. Vets suggest twice-yearly checks from then โ this calculator flags the stage as you slide.