Dog Age Calculator
Enter your dog's age and adult size to see the human-age equivalent. The calculator uses the veterinary size chart (small dogs age slower after year two) and shows the UCSD epigenetic formula alongside — the old "multiply by 7" rule is off by years.
How dog years convert to human years
Dogs mature extremely fast at first and slower later, so the conversion isn't linear. The widely used veterinary chart counts the first year as about 15 human years and the second as about 9 more (24 total at age two). After that, each dog year adds roughly 4 human years for small dogs, 5 for medium, 6 for large and 7 for giant breeds — bigger dogs age faster and live shorter lives.
A 2020 study at UC San Diego (Cell Systems) compared DNA methylation in Labradors and humans and fitted the formula below for adult dogs. It front-loads even more aging into the first years — a 1-year-old dog maps to a ~31-year-old human — and converges with the chart later in life.
Worked examples
Example 1: a 5-year-old medium dog
A 5-year-old, 35 lb dog — how old in human years?
- The first two years count as about 24.years 1–2 → 24
- Three more years at the medium rate of 5.24 + 3 × 5 = 39
- The epigenetic formula for comparison.16 × ln(5) + 31 ≈ 56.7
About 39 human years by the chart (the epigenetic clock says ~57 — it runs higher for young adult dogs).
Example 2: small vs giant at age 10
How different is age 10 for a Chihuahua and a Great Dane?
- Chihuahua (small): 24 + 8 × 4.24 + 32 = 56 human years
- Great Dane (giant): 24 + 8 × 7.24 + 56 = 80 human years
56 vs 80 human years — at ten, a giant breed is already in old age while a small dog is middle-aged.
Example 3: an 8-month-old puppy
How old is an 8-month-old puppy in human terms?
- Convert the age to a fraction of a year.8 months = 8 ÷ 12 ≈ 0.67 years
- Prorate the 15-human-year first year.0.67 × 15 = 10
About 10 human years — roughly a pre-teen, which matches puppy behavior.
FAQ
Isn't one dog year just seven human years?+
No — that old rule assumed dogs live ~10 years and humans ~70. It underestimates early aging (a 1-year-old dog can already reproduce) and overestimates later aging, especially for small breeds.
Why do small dogs "age slower" than big dogs?+
Larger breeds live notably shorter lives — Great Danes average 8–10 years, Chihuahuas 14–17. The per-year rates (4 to 7 human years) encode that observed difference after the fast puppy phase.
What is the epigenetic dog-age formula?+
Researchers at UC San Diego (Wang et al., Cell Systems 2020) matched DNA-methylation patterns of Labrador retrievers to humans and derived human age ≈ 16 × ln(dog age) + 31 for dogs one year and older. It was built on one breed, so treat it as a scientific estimate, not a vet diagnosis.
Is this the same as 'canine age'?+
Yes — a canine age calculator converts the same way; this page covers both. For cats the first-two-years numbers are similar (≈24) but the later rate is a flat ~4 per year.
At what age is a dog a senior?+
Vets commonly call small dogs senior around 10–11, medium around 8–10, large around 8, and giant breeds as early as 6–7 — roughly when the chart passes ~55–60 human years.
Related calculators
- Dog Food CalculatorHow much to feed your dog: daily calories from the veterinary RER formula and life-stage factors, converted to cups of your actual food — steps shown.
- Puppy Weight CalculatorEstimate your puppy's adult weight from its current weight, age and expected size class, using the published milestone rules — with the math and caveats shown.
- Age CalculatorFind exact age from a date of birth: years, months and days, total days lived, and the date of the next birthday — with the calendar math shown.