Dog Age Calculator
Convert your dog’s age to human years using the size-adjusted method vets actually use — not the old “multiply by 7” myth.
How it works
human years = 15 (year 1) + 9 (year 2) + size increment × (age − 2), where the increment is 4 (small), 5 (medium), 6 (large) or 7 (giant)
Dogs mature fast then level off, so a flat multiplier never fits. The first year is worth about 15 human years and the second adds another 9 (reaching 24), after which each extra year adds a fixed amount that grows with body size — small breeds age slowest, giant breeds fastest. That size split is why a Great Dane is “elderly” years before a Chihuahua of the same age.
Worked example
A 5-year-old medium dog: 15 for year one, +9 for year two (24), then +5 for each of years three, four and five — 24 + 15 = about 39 human years. The ×7 rule would have guessed 35, and it is even further off for very young or giant dogs.
Frequently asked questions
Isn’t one dog year just seven human years?
No — that rule is a decades-old myth with no scientific basis. Dogs reach the equivalent of a teenager within their first year, so the curve is steep early and flatter later, and it depends heavily on size.
Why does size change the answer?
Larger dogs have shorter lifespans and age faster once grown, so each adult year counts for more human years. A giant breed at 8 is far more “senior” than a small breed at 8.
How accurate is this?
It is a well-regarded rule of thumb, not a lab measurement. A 2020 epigenetic-clock study refined the curve further, but for everyday use the size-adjusted method here is close and easy.
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This calculator is for educational purposes. Double-check important results before acting on them.