Multiplying by 7 gets it wrong at both ends
By the ×7 rule a one-year-old dog would be a seven-year-old child — in reality, at one a dog is already past puberty and nearly full grown. And old dogs age more slowly than ×7 suggests. The rule survives because it is easy, not because it fits.
The first two years are the fastest
This calculator uses the method common in vet charts: the first year counts as 15 human years, the second adds 9, and every year after that adds a steady amount. A two-year-old dog or cat is therefore already around 24 in human terms.
Big dogs age faster than small ones
From the third year on, each year adds 4 human years for a small dog (under 10 kg), 5 for a medium one and 6 for a large one. The same ten-year-old works out to about 56 human years if small and about 72 if large. Cats vary little in size, so one value — 4 — covers them all.
While you’re here — claim a crypto exchange bonus
More calculators
Frequently asked questions
Q. How accurate is this?
It is a rough average from vet charts. Breeds and individuals vary widely, so do not use the result to judge health — use it to think about how often a check-up makes sense.
Q. Why do large dogs age faster?
Across species, bigger animals usually live longer — within dogs it flips. Growing fast seems to carry a cost: a Great Dane is elderly at 8, while many small terriers reach 15. Cats barely vary in size, which is why one curve is enough.
Q. Can I enter a fraction like 0.5?
Yes. Within the first year the count runs proportionally, so a six-month-old puppy is about 7.5 in human years — already a child rather than a baby. That is exactly where the ×7 rule falls apart.