Dog Age Calculator
Dog aging varies by breed size - enter your dog's age and size to get a more accurate human-year estimate than the old 'multiply by 7' rule.
Last updated: September 25, 2026
Frequently asked questions
Is 'one dog year equals seven human years' accurate?
No - that old rule is a rough myth. Dogs age faster in their first two years, and larger breeds age faster in later years than small breeds.
Why do larger dog breeds age faster than small breeds?
Large and giant breeds grow faster and hit physical maturity sooner, which is linked to shorter lifespans and faster aging in their middle and senior years - the opposite of the pattern in most other mammals.
At what age is a dog considered a 'senior'?
It varies by size - small breeds are typically considered senior around 10-12 years, medium breeds around 8-10, and large or giant breeds as early as 6-7 years, since larger dogs both mature and age faster than smaller ones.
Why isn't the calculation just size-based - does breed matter too?
Size remains the strongest predictor of aging rate, which is why this calculator groups breeds by size (small, medium, large, giant) rather than using a single universal formula. Individual breeds within the same size class can still age at slightly different rates due to genetics, but size explains most of the variation.
What's the difference between 'dog years' and this calculator's human-year equivalent?
'Dog years' usually refers to the flawed 7:1 multiplier. This calculator instead applies a curve that front-loads aging in the first two years and adjusts the later rate by size class, which is much closer to how veterinarians actually describe canine aging.
How old is a 5-year-old giant breed dog in human years?
A 5-year-old giant breed (like a Great Dane) works out to roughly 40 human years - notably older than a 5-year-old small breed, which lands closer to 36, because giant breeds age faster once past puppyhood.
Can I use this calculator for a mixed-breed dog?
Yes - since the formula keys off size rather than breed identity, just select the size category (small, medium, large, or giant) that best matches your mixed-breed dog's adult weight for the most relevant estimate.