Convert your dog or cat age into human years using the real non-linear curve — the "times 7" rule is a myth.
Multiplying by seven is the most repeated piece of pet arithmetic and it is wrong. It comes from dividing a 70-year human life by a 10-year dog life, and it fails at both ends: a one-year-old dog is already sexually mature, closer to a teenager than to a child of seven. Ageing is fast at the start and then slows down. In the chart used by the AVMA and the American Kennel Club, the first year of a dog is worth about 15 human years, the second adds roughly 9 more (24 in total), and each year after that adds around 4 for a small dog, 5 for a medium one, 6 for a large one and 7 for a giant breed. Cats follow a similar curve: 15, then 24, then about 4 per year.
The calculator interpolates that chart instead of applying a single multiplier. Dogs are split into the four size bands the chart uses — up to 9 kg, 10 to 22 kg, 23 to 40 kg and over 40 kg — because body mass is the strongest known predictor of ageing speed in dogs, an inversion of the usual rule where bigger species live longer. Months are interpolated between the yearly anchors, and beyond 16 years the last yearly step is carried forward. The life stage follows the AAHA model — puppy or kitten, young adult, adult, senior, geriatric — as fractions of the average life expectancy for that profile, which is why a 10-year-old Great Dane is already geriatric while a dachshund of the same age is merely adult.
For dogs the panel also shows a second estimate, from a 2020 study by Wang and colleagues at UC San Diego that compared DNA methylation in Labradors and humans. Their epigenetic clock gives human age ≈ 16 × ln(dog age) + 31, and appears here as a curiosity: it was calibrated on a single breed and ignores size. All of these numbers are averages, not a diagnosis — breed, weight, neutering and genetics shift the curve, and your vet is the only source that knows your animal. The calculation runs entirely in your browser.
Dogs: the first year counts as about 15 human years, the second adds about 9 (24 in total), and each following year adds roughly 4 (small), 4 to 5 (medium), 5 to 6 (large) or 7 (giant), interpolating the AVMA/AKC chart by size band; months are interpolated between the yearly anchors. Cats: 15 in the first year, 24 by the second, then about 4 per year. Epigenetic estimate for dogs (Wang et al., 2020): human age ≈ 16 × ln(age in years) + 31.
No — it is a myth with no scientific basis. Dogs mature far faster at the beginning (the first year alone is worth about 15 human years) and then age more slowly, at a rate that depends on size. The ×7 rule only looks plausible in the middle of a medium dog life.
Because large dogs age faster than small ones. A 9 kg dog often lives 14 years while a dog over 40 kg averages 9, so the same calendar year costs a giant breed far more in human terms.
A one-year-old cat is roughly 15 in human terms, a two-year-old about 24, and every year after that adds around 4 — so a 10-year-old cat is close to a 56-year-old person. Cats age more uniformly than dogs, having nothing like the size range of dog breeds.
It comes from a 2020 study that measured DNA methylation — chemical marks that accumulate with age — in Labradors and humans, giving human age ≈ 16 × ln(dog age) + 31. It is a biological clock rather than a rule of thumb, but it was calibrated on one breed and ignores size.
In the last quarter of its expected lifespan, which is what the life stage field shows: around 10 years for a small dog, 8 for a large one, 7 for a giant breed and 11 for a cat.
No. The curve is embedded in the page and the calculation runs in JavaScript on your device — nothing is sent to a server or stored.
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