Dog Age in Human Years: The Full Conversion, Explained
A dog's age in human years is not the calendar times seven. Here is the full conversion: where the numbers come from, why models disagree, and the calculator to run your own dog's age through.
In human years
39human years
Life stage: adult
Maintenance years: steady weight and activity matter more than milestones.
For comparison, the epigenetic clock from Wang et al. (2020) puts a medium dog of this age at about 56.8 human years. Different published models disagree; see how the math works.
Why dividing by seven gets your dog's age wrong
The divide-by-seven rule compares an average human lifespan with an average dog lifespan and treats the ratio as a conversion rate. It breaks down immediately at the start of life: dogs reach adulthood within roughly two calendar years, and the AVMA-based model puts a 1-year-old dog near 15 human years, not 7.
It also breaks down by size. A Great Dane and a Chihuahua with the same birthday are not the same biological age, which is why every serious conversion is size-adjusted.
Dog age in human years calculator
The calculator at the top of this page takes three inputs. Size class: small (up to 20 lb), medium (21-50 lb), large (51-100 lb) or giant (over 100 lb). Years and months: use months for puppies and for precision on older dogs.
The result shows human years on the size-adjusted model, the life stage, and, from age one and up, the epigenetic-clock figure from Wang et al. (2020) for comparison.
Worked examples: puppy, adult and senior dogs
Puppy
6 months, small dog
7.5human years
Half a calendar year is already a meaningful slice of a puppy's growth.
Adult
5 years, medium dog
39human years
Epigenetic clock (Wang et al. 2020): about 56.8.
The two published models part ways: lifespan ratios say 39, the methylation clock says about 57.
Senior
12 years, large dog
84human years
Epigenetic clock (Wang et al. 2020): about 70.8.
Deep into senior for a large dog, whatever model you read the chart with.
Sources for the conversion models
The calculator is an educational approximation. These references explain the size-adjusted chart and the separate epigenetic model mentioned on this page.
Keep going
Prefer to start from the top? The dog age calculator handles the conversion with the full chart, or read how old is my dog if there is no known birthday.