Updated
Dog age calculator
Two answers, because there are two honest ways to convert dog years: the size rule vets have used for decades, and the 2020 DNA-methylation study that found dogs age fast early and slowly later. The size rule is the everyday answer; the study is the biological one, and it applies from one year old.
34 human years
Life stage: mature adult. A medium dog counts as senior from 9 years.
- Size rule (AVMA): 15 for year one, +9 for year two, then +5 a year for a medium dog
- 34 human years
- Study estimate: 16 ln(age) + 31 (Wang et al. 2020, Labrador-derived)
- 53.18 human years
- Life stage (AAHA 2019)
- mature adult
- Senior from
- 9 years for a medium dog: twice-yearly exams, weight and dental checks from then on
What this means
The two numbers differ most for young dogs. The study says a one-year-old dog is already about 31 in human terms, because early development is fast; the size rule says 15. From middle age on they converge, and by eight years a medium dog is 54 by the rule and 64 by the study.
Size matters after the second year. Giant breeds age faster than small ones — about seven human years for every dog year against four — which is why the rule asks for adult size rather than breed.
Senior is a size question too: 11 years for a small dog, 9 for medium, 7 for large and 5 for giant breeds, taking the lower bound of the AAHA range for each.
When to see a vet
- Your dog has crossed into the senior stage: AAHA recommends check-ups twice a year from then on, with weight and dental checks each time.
- Any sudden change in weight, thirst, appetite, breathing or mobility, at any age.
- A senior dog that is drinking or urinating more than it used to — an early sign of kidney or endocrine disease that is far easier to treat when caught.
Formula and sources
Sources reviewed 18 September 2026. Each names the figure it supports.
- Size-rule result (15, +9, then +4 to +7 a year by size) — American Veterinary Medical Association guideline for dog years to human years, as stated by the American Kennel Club, "How to calculate dog years to human years"
- Study-based estimate, 16 ln(age) + 31, dogs of one year and older — Wang T. et al., "Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome", Cell Systems 11(2), 2020 (epigenetic clock fitted to 104 Labrador retrievers)
- Life stages and the senior threshold by size — AAHA Canine Life Stage Guidelines, 2019
This page is an educational estimate, not veterinary advice.
Frequently asked questions
How old is my dog in human years?
Use the size rule above: about 15 human years for the first dog year, 9 for the second, then 4 to 7 a year depending on size. A 4-year-old medium dog is about 34; the same dog is 53 by the 2020 study formula.
Is one dog year seven human years?
No. The "times seven" rule assumes dogs age evenly, and they do not: a one-year-old dog is sexually mature, which a seven-year-old child is not. Both methods here front-load the early years and slow down later.
When is a dog a senior?
It depends on size: from about 11 years for small dogs, 9 for medium, 7 for large and 5 for giant breeds, following the AAHA canine life-stage guidelines. From then on, twice-yearly check-ups.
What is the 16 ln(age) + 31 formula?
A 2020 study of DNA methylation in Labrador retrievers (Wang et al., Cell Systems) found dog and human ages line up on a logarithmic curve: human age = 16 × the natural log of the dog’s age + 31. It was fitted to dogs of one year and older, so this page does not apply it to puppies.
Can I enter my puppy’s age in months?
Yes: enter 0 years and the months. Under one year the size rule is stretched in proportion to the first-year figure of 15, and the result is labelled interpolated, because the rule itself only speaks in whole years.