Pet Age Calculator
Convert your dog's or cat's age into human-equivalent years using modern non-linear veterinary formulas — the 2019 epigenetic-clock formula (breed-size adjusted) for dogs and the 15-9-4 rule for cats. Not the old "multiply by 7" myth.
Input
Decimal years are allowed (e.g. 0.5 for a 6-month-old)
Larger breeds age faster in mid-to-late life than small breeds
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
The Pet Age Calculator converts your dog's or cat's age into human-equivalent years — using modern, non-linear veterinary formulas instead of the old "1 dog year = 7 human years" myth. That rule of thumb was never accurate: pets mature much faster in their first couple of years and then age more slowly (or, for large dog breeds, faster again later in life) than a flat multiplier can capture.
How it works
Dogs use the 2019 epigenetic-clock formula published by Wang et al., which compares DNA methylation patterns in dogs and humans to model biological aging:
human age = 16 x ln(dog age) + 31
This logarithmic curve fits reality far better than a linear multiplier: a 1-year-old dog is already roughly 31 in human terms (most skeletal and sexual maturity happens in year one), a 2-year-old is about 42, and the curve flattens at older ages rather than climbing forever. Because breed size measurably affects aging — large and giant breeds tend to have shorter lifespans and age faster later in life, while small breeds age more slowly after maturity — the result is scaled by a breed-size factor (small x0.92, medium x1.0, large x1.10, giant x1.20). For puppies under 1 year old, where the logarithm isn't defined, the tool ramps linearly from 0 to 31 human years across that first year.
Cats use the standard "15-9-4" rule vets reference: year one counts as 15 human years, year two adds 9 more (24 total by age 2), and every year after adds 4. Decimal ages interpolate linearly within whichever bracket they fall in.
Both species also get a life stage label (Puppy/Kitten through Geriatric) based on the resulting human-equivalent age.
How to use it
- Enter your pet's age in years — decimals are fine (e.g.
0.5for a 6-month-old,4.5for four and a half years). - Choose Dog or Cat.
- If you chose Dog, pick the closest Dog Size category by adult weight (small, medium, large, or giant).
- The result updates automatically and shows the pet's age, species (and size), human-equivalent age, life stage, and which formula was used.
Results can be copied or downloaded as a CSV file.
FAQ
Why not just multiply by 7?
The "7 human years per dog year" rule dramatically understates how fast pets mature early on and doesn't hold up later in life either. A 1-year-old dog isn't 7 in human terms — it's already sexually mature and closer to a human teenager, which is why both formulas here front-load most of the aging into the first one to two years.
Why does dog size matter?
Larger dog breeds generally have shorter overall lifespans and age faster once past early adulthood, while small breeds tend to live longer and age more gradually. The breed-size factor is a multiplier on the base epigenetic-clock result — it nudges the estimate up for large/giant dogs and down for small dogs, rather than changing the shape of the curve itself.
Is this formula exact for my specific pet?
No single formula accounts for individual genetics, health history, or exact breed — treat the result as a well-grounded estimate, not a veterinary diagnosis. The dog formula is based on published epigenetic research; the cat formula is the general rule of thumb used across the veterinary field.
Is my data sent anywhere?
No. The pet age and species you enter are processed entirely in your browser — nothing is uploaded or stored, and the calculation works the same way offline.