Dog years to human years, by size

Why times seven doesn’t work

Multiplying by seven treats every dog year the same. A 1-year-old dog would be 7 in human terms, yet VCA Animal Hospitals notes that small and medium breeds are mature by about 10 to 12 months. A 1-year-old Beagle is closer to a young adult than to a second grader.

The rule fails in the other direction too. It ignores size, even though large and giant breeds have shorter average lives than small ones. A 2023 study of clinic records (Montoya et al.) found an average life expectancy of about 13.5 years for small breeds and about 9.5 years for giant breeds. A 9-year-old Chihuahua and a 9-year-old Great Dane are at very different points in their lives.

The chart

The chart uses the guideline from the American Veterinary Medical Association (AVMA) as the AKC quotes it: 15 human years for the first year, about 9 for the second, then about 5 a year for a medium-size dog. For other sizes we scale the yearly step to average life expectancy by size from Montoya et al., so small dogs age a little slower and giant dogs faster. That scaling is our own derivation, explained on the methodology page.

Use the chart as a rough guide to life stage, not as a precise age. The giant-breed column passes 100 at 14 because few giant dogs live that long; read those rows as “very old” rather than an exact age. To find your own dog’s age, including months, use the dog age calculator.

The DNA clock

In 2020, researchers at UC San Diego compared age-related chemical changes in the DNA of 104 Labrador Retrievers with the same changes in people. Their formula is human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. It says dogs age very fast early on, then much more slowly.

The two methods agree around age 10 and disagree at both ends. The DNA clock is the newer science, but it was built from one breed. Small breeds, which live longer, may not follow the same curve, and the study can’t tell us how well it fits a Chihuahua or a Great Dane. That’s why our calculator shows the DNA clock next to the size-adjusted vet rule instead of on its own.

Puppies under a year

Neither method is built for young puppies. The DNA clock formula gives meaningless results for very young puppies (we don’t use it below 8 weeks), and the vet rule only gives the 1-year point. For the first year our calculator spreads the 15 years evenly, so a 6-month-old puppy shows as about 7 to 8 human years. That is our interpolation, not a published figure, and it likely understates how fast puppies mature early on.

What the number is good for

The most useful thing about a human-years number is the life stage it points to. The 2019 AAHA life stage guidelines call a dog senior in the last 25% of its expected lifespan. Using life expectancy by size, that comes out at about 10 years for toy and small dogs, about 9.5 for medium dogs, about 8.6 for large dogs and about 7 for giant breeds, by our calculation.