Pet Age Calculator (Dog + Cat Years)
Convert your dog or cat's age into 'human years' using the modern 2019 UCSD epigenetic-clock formula for dogs, and a common veterinary piecewise chart for cats. Better than the old 'multiply by 7' rule of thumb.
Last updated: September 2026
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About this calculator
The classic 'one dog year equals seven human years' rule is a broad oversimplification. A 1-year-old dog is roughly a teenager, not a 7-year-old child. In 2019, researchers at UC San Diego (Wang et al., Cell Systems) published an epigenetic clock based on methylation patterns in dog and human DNA that produced a much cleaner mapping: human-equivalent age ≈ 16 × ln(dog age) + 31 for dogs older than about 1 year.
Under that formula, a 1-year-old dog maps to about 31 human years (a young adult), a 4-year-old to about 53, and a 14-year-old to about 73. Puppies age much faster than the log curve suggests, so this calculator uses a linear approximation for dogs under 2 (roughly 15 human years by the first birthday, another 9 by the second).
Cats follow a different but well-documented piecewise schedule commonly published by AAHA and Cornell: about 15 human years by age 1, 24 by age 2, then roughly 4 human years per cat year after that. A 10-year-old cat is thus around 56 human years — middle-aged, not elderly.
All of these are averages. Breed size matters enormously for dogs — large breeds like Great Danes age faster than small breeds like Chihuahuas — and health, weight, and genetics all shift the real biological age up or down. Use the number as a rough guide, not a medical assessment. For questions about senior care thresholds, ask your vet.
How to use
Example — a 5-year-old Labrador. Enter species = 'dog', petAgeYears = 5. Formula: 16 × ln(5) + 31 = 16 × 1.6094 + 31 = 25.75 + 31 = 56.75, rounded to 57 human years. That's roughly a person in their late 50s — middle-aged, likely graying, still active but not a puppy. Example — a 10-year-old cat. Enter species = 'cat', petAgeYears = 10. Formula (piecewise): 24 + (10 − 2) × 4 = 24 + 32 = 56 human years. Middle-aged. Regular vet checkups (twice a year is the AAHA senior recommendation) become important around this point. Track visits with the day-counter at /en/calculators/time-zones/day-counter/.
Frequently asked questions
Why not just multiply by 7?
The 'one year = seven years' shortcut assumes a linear mapping, but pets don't age linearly. Dogs and cats mature rapidly in their first two years, then slow down. A 1-year-old dog is essentially a teenager (about 15 human-equivalent years), not a 7-year-old. The log formula matches biology much better in the middle and senior years.
Does breed size affect a dog's aging?
Yes, substantially. Large breeds (Great Dane, Saint Bernard) age faster than small breeds (Chihuahua, Maltese). A 10-year-old Great Dane is considered geriatric, while a 10-year-old Chihuahua is often middle-aged. The UCSD log formula uses Labrador Retriever data as a mid-size baseline, so it under-estimates aging for giant breeds and over-estimates it for tiny breeds. Adjust your interpretation up for large dogs, down for small ones.
Where does the cat formula come from?
The piecewise cat mapping is widely used by the American Animal Hospital Association (AAHA) and Cornell Feline Health Center: about 15 human years in the first year of life, an additional 9 in the second year (total 24 at age 2), then about 4 human years per cat year after that. It matches observed lifespan patterns — indoor cats commonly live 15–20 years, mapping to 76–96 human-equivalent years, which lines up with human longevity.
Is my pet a senior?
Rule of thumb: cats become senior around age 10 (≈56 human), dogs around 7–8 (≈47–51 human), with earlier onset for large breeds. Vets typically recommend twice-yearly checkups and bloodwork once your pet is 'senior'. This calculator is for curiosity; ask your vet for a real assessment of your pet's stage of life.