Dogs and cats: human-age benchmarks
At 2, a cat and a small, medium or large dog are all about 24 in human years, and all about 36 at 5. After that, a cat or a small dog keeps the same pace while a medium or large dog ages faster: at 10, a cat is about 56, a medium dog 60 and a large dog 66.
| Pet's age | Cat | Small dog | Medium dog | Large dog |
|---|---|---|---|---|
| 1 year | 15 years | 15 years | 15 years | 15 years |
| 2 years | 24 years | 24 years | 24 years | 24 years |
| 5 years | 36 years | 36 years | 36 years | 36 years |
| 10 years | 56 years | 56 years | 60 years | 66 years |
| 15 years | 76 years | 76 years | 83 years | 93 years |
How age in human years is calculated
The first year is worth about 15 human years, the second adds 9 (24 by age two), then each following year adds a few human years. For dogs, that pace depends on size: large breeds age faster than small ones, and a giant breed, counted 12 at age 1, pulls ahead from its third year.
The "one pet year equals seven human years" myth
This simple rule is wrong. Dogs and cats become adults in barely one to two years, then age more slowly. One early year of life is worth far more than seven human years, while a year late in life is worth less.
An estimate, not a diagnosis
This calculator gives a ballpark figure. Every animal ages at its own pace, and only a vet can properly assess its health.
Our sources
- Method (dog), from age 1: the values of the "Comparative Age of Dogs and Humans" chart in the Dog Owner's Home Veterinary Handbook (Eldredge et al., 4th edition, 2007), from 1 to 16, taken as printed, with interpolation between birthdays. Its sizes, given in pounds, match ours: small up to 20 lb (9 kg), medium 21 to 50 lb (9.5 to 23 kg), large 51 to 100 lb (23 to 45 kg), giant over 100 lb (45 kg).
- Method (cat), from kitten to old age (4 at 3 months, 10 at 6 months, 15 at 1 year, 21 at 18 months, 24 at 2 years, then 4 years a year): the chart in the AAFP-AAHA feline life stage guidelines, Hoyumpa Vogt et al., Journal of Feline Medicine and Surgery, 2010. doi.org
- Dog and cat life expectancy: Montoya et al., "Life expectancy tables for dogs and cats derived from clinical data", Frontiers in Veterinary Science, 2023 (US veterinary clinic records, figures checked on 31 October 2026). doi.org
- Why large dogs age faster: Kraus, Pavard and Promislow, "The size-life span trade-off decomposed: why large dogs die young", The American Naturalist, 2013 (74 breeds). doi.org
- Dog life stages: the AAHA canine life stage guidelines, 2019 (the senior stage starts at the last quarter of life expectancy, and the first heat comes anywhere from 4 months in some small breeds to 24 months in some large ones). doi.org
- Cat life stages: the AAHA / AAFP feline life stage guidelines, 2021. catvets.com
- Puppy age before 1 year and the DNA method (dog): Wang et al., "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome", Cell Systems, 2020 (dog developmental stages lined up with human ones, 2 months ≈ 1 year and 6 months, puberty, ≈ 12, and the formula 16 × ln(age) + 31, derived from Labradors). doi.org
Going further
Welcoming an animal well also means planning ahead and being ready to react.
FAQ - Frequently asked questions
Is the age-times-seven rule accurate?
No. It's far too simple. Dogs and cats age very fast in their first two years, then slow down. A dog's size changes everything too: large dogs age faster than small ones.
Do dogs age faster than cats?
Not before 5, except for giant breeds. A cat and a small, medium or large dog are all about 24 in human years at 2 and 36 at 5. After that, a cat or a small dog keeps the same pace while a medium or large dog ages faster: at 10, a cat or a small dog is about 56, a medium dog 60 and a large dog 66. A giant breed pulls ahead from its third year: about 45 at 5 and 79 at 10.
Why does size matter for dogs but not for cats?
Dog breeds vary enormously in size, and big dogs age faster: a giant breed lives 9.5 years on average, a small dog 13.5. Cats vary little in build, so one curve fits them all.
How do I convert human years to dog or cat years?
Read the same chart backwards. For a cat and for a small, medium or large dog, 15 human years is age 1 and 24 is age 2. For a cat, beyond 24 human years, subtract 24, divide by 4, then add 2. For a dog, the pace then depends on size: the dog age calculator works it out for every size, and the cat one for your cat.
Do I need to pick dog or cat?
Yes. The two species follow different curves. Pick the page for your animal to get a tailored estimate.
Is the tool really free and ad-free?
Yes. Animalert is a non-profit. No account, no ads, no data collected: the calculation runs directly on your device.