Dog & Cat Age in Human Years Calculator
Find your pet's age in human years. Dogs age fastest in their first two years and then at a pace that depends on size, and cats follow the veterinary life-stage guidelines. Choose the size-based veterinary table or the newer epigenetic clock formula for dogs, then see the life stage and common checkup timing.
Written by Suhaib Hassan. Human-year figures are approximations, not medical advice. Our methodology.
It reads your pet's age from a size-based table, or applies a logarithmic formula from dog DNA methylation research.
The old 1 dog year = 7 human years rule is wrong for young pets. This uses curves that match how animals really age.
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Dog and cat age chart
Human-year equivalents from the size-based dog table and the cat guideline. Values are approximate and vary by breed and individual.
| Pet age | Small dog | Medium dog | Large dog | Giant dog | Cat |
|---|
Cats: indoor and outdoor lifespans
The aging rate of a cat is the same on paper, but the years a cat gets to live are not. Lifestyle and health care matter greatly, and figures below are broad ranges.
Indoor only
Commonly 12 to 18 years or more, equal to roughly 64 to 88 human years. Lower risk of trauma, infectious disease and toxins.
Lowest riskIndoor and outdoor
Often shorter, since traffic, fights, parasites and infections add risk.
Moderate riskOutdoor or feral
Life expectancy is often far lower because of weather, hunger, injury and untreated disease.
Highest riskHow the ages are estimated
Epigenetic clock (dogs)
human = 16 × ln(dog age) + 31Size-based table (dogs)
first year 15, second 24, then a yearly rate that grows with sizeCats
year 1 = 15, year 2 = 24, then +4 per yearThe 7-year rule is a myth
A one-year-old dog is closer to a mid-teen person than a 7-year-old child, and large dogs age faster in later life than small ones. The formulas here reflect that.
No conversion is exact. Genetics, diet, exercise and health care all change how an individual pet ages.
Worked examples
Illustrative pets, each checked by hand. The first is the default.
5.5-year-old medium dog
Size-based table.
halfway: 36 + 0.5 × 6 = 39 human years
Same dog, epigenetic clock
5.5 years.
16 × 1.7047 + 31 = 58.3 human years
8-year-old cat
Life-stage guideline.
+ 6 × 4 = 48 human years
How to convert dog and cat years to human years
- Choose dog or cat, and for a dog pick its size by adult weight.
- Enter the age in years and months.
- Read the equivalent human age and the life stage.
- Use the life stage to plan checkups, dental care and senior screening with your vet.
The two dog methods give different answers, especially in older dogs. Treat both as rough guides and rely on your vet's judgement for your own pet.
By Suhaib Hassan · Reviewed 29 September 2026 · How CalculatePilot verifies formulas →
Sources
- Wang T. et al. (2020), Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome, Cell Systems 11(2).
- AAHA/AAFP, Feline Life Stage Guidelines (2021).
- AAHA, Canine Life Stage Guidelines (2019).
- Size-based dog age chart, as published by veterinary schools and animal health organisations.
Frequently asked questions
How old is my dog in human years?
It depends on age and size. A medium dog aged 5 is about 36 human years by the veterinary table, and the epigenetic formula gives a higher figure for the same age. Enter your dog's details above.
Why do large dogs age faster?
Larger breeds grow quickly and tend to have shorter lifespans, so each later calendar year represents more biological aging than for a small dog. Giant breeds often reach senior status by 6 to 7 years.
How do I calculate a cat's age in human years?
The common guideline counts the first year as 15, the second year as 24, and then adds 4 for each year after that. A 10-year-old cat is about 56 human years.
What is the epigenetic clock formula?
Researchers at the University of California San Diego compared DNA methylation in dogs and humans and found human age ≈ 16 × ln(dog age) + 31. It was developed from Labrador retrievers, so it may not fit every breed.
When is a pet a senior?
Cats are considered mature at 7 to 10 years and senior from about 11. Dogs become senior earlier the larger they are, from roughly 6 to 7 for giant breeds to 10 or more for small dogs.
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