Dog & Cat Age Calculator — pet years to human years
Convert your dog's or cat's age into human years using the size-based chart vets use, not the old “× 7” rule.
What this calculates
The old rule of multiplying by seven is wrong at both ends. Cats and dogs grow up far faster than that — a one-year-old is roughly a 15-year-old in human terms, and a two-year-old about 24 — and then the pace slows. After two, how fast a dog ages depends on its size: small breeds age more slowly and live longer, giant breeds age fastest. This calculator uses the size-based chart vets commonly use. For dogs it also shows an estimate from a 2020 study that compared changes in dogs' and humans' DNA over a lifetime; it is a useful second opinion, and a reminder that “human years” is an analogy rather than an exact measurement.
Formula
first year human = 15 × age
second year human = 15 + 9 × (age − 1)
after two human = 24 + per-year × (age − 2)
per-year: cat or small dog 4, medium 5, large 6, giant 7
DNA-based (dogs) human = 16 × ln(age) + 31 Example
A six-year-old medium-sized dog is 24 human years at two plus 4 × 5 = 20 more, so about 44. The DNA-based estimate puts the same dog at about 60 — the two methods agree for young adult dogs and drift apart later, which is why vets talk about life stages rather than exact human ages.
Frequently asked questions
Is one dog year really seven human years?
No. That rule makes a one-year-old dog a seven-year-old child, when most one-year-old dogs are physically adults. The first two years count for about 24 human years, and later years count for 4 to 7 depending on size.
Why do big dogs age faster?
Large and giant breeds grow quickly and have shorter lifespans, so each year is a bigger share of their life. A Great Dane is often considered senior at six or seven, a Chihuahua not until ten or later.
How old is my cat in human years?
About 15 at one year, 24 at two, then roughly four human years for each year after that — so a ten-year-old cat is about 56, and a cat of 15 is about 76.
When is a pet a senior?
Cats are usually considered senior from around 10–11. For dogs it depends on size, from about 6 for giant breeds to 10 or more for small ones. Many vets suggest twice-yearly check-ups from then on.